Supporting You with Application and Technical Services
Q-Sense provides service and support through many different channels. Search out the QCM-D FAQ to find the answer to your technical or application related question. If you don’t find it there, our Application Specialists will be happy to support. We frequently offer live training webinars where our Application Scientists guide you in, for example, data analysis or specific applications. In order to help you get the most out of your Q-Sense instrument, start-up training is included as part of each system purchase. Q-Sense also offers you the possibility to develop your knowledge and skills further, with Q-Sense Scientific Meetings as well as customized training courses. In the Download Center you can find our application notes, brochures, animations and more.
“Q-Sense has, by far, the most friendly and helpful customer service that we deal with on a regular basis.”
– Professor Rick Davis and his student Will Miles, at the Department of Chemical Engineering, Virginia Tech, USA
What is the difference between QCM-D and traditional QCM?
The Quartz Crystal Microbalance with Dissipation monitoring (QCM-D) technology measures the frequency and dissipation of the freely oscillating quartz crystal after excitation. As opposed to ordinary QCM, the QCM-D determines the dissipation factor, providing information about conformational changes and softness/rigidity (viscoelasticity) of the molecules studied. The major benefits with this procedure compared to other QCMs are:
- Measurements are extremely rapid, with a kinetic resolution of up to 200 data points per second. The high measurement rate results in high sensitivity since several data points can be used to average data.
- The response of the crystal is recorded when it is not part of a feedback loop (active oscillation circuit). This means that the instrument only records changes occurring at the surface. In conventional QCMs, part of the recorded changes in resonant frequency is due to changes in the feedback loop (such changes occur when the mechanical load on the crystal changes) and not due to changes taking place at the surface.
What is dissipation?
The dissipation (damping) is the sum of all energy losses in the system per oscillation cycle. It is defined as: 1/Q, where ‘Q’ is the quality factor of the oscillator. It can also be defined as the energy dissipated per oscillation, divided by the total energy stored in the system. With QCM-D, the dissipation factor is measured every time the drive generator output is stopped and the sensor oscillation starts to decay exponentially. A soft film attached to the quartz crystal is deformed during oscillation, which gives high dissipation. In contrast, a rigid material follows the crystal oscillation without deformation and consequently gives low dissipation.
Why is it important to measure the energy dissipation?
The frequency response of a quartz crystal represents the change of total mass in the measurement. This mass always includes a certain amount of water. However, the proportion of water may vary between 10% and 90% depending on the type of molecule and the way it adsorbs to the surface (an elongated protein that adsorbs flat on the surface gives low dissipation while the same molecule standing up on the surface gives high dissipation). By measuring the dissipation, it is possible to determine if a soft film (water rich) or a rigid film (less water) has formed on the surface. The Sauerbrey relation gives a good estimation of adsorbed mass only when the film is fairly rigid. Measuring the dissipation means that it is possible to determine whether the Sauerbrey relation is valid. The dissipation factor gives additional ‘structural’ information, compared to an ordinary QCM measurement, in that one can measure the conformational change of the film, e.g., crosslinking (collapse) and swelling.
How is the sensitivity distributed over the crystal surface?
The sensitivity of the sensor is highest in its center, and decreases towards the sensor edge. When calculating mass and viscoelastic properties of an adsorbed layer, the software QTools assumes that the surface has been homogeneously coated, and so the result is always an average of, for instance, mass per area unit. In other words, it is not relevant to talk about sensitivity or results of specific regions of the sensor surface, and any approach to partially cover the sensor is therefore not recommended. The decrease in sensitivity towards the edge is illustrated in the image below.
What is the difference between QCM-D and SPR measurements?
The ability to evaluate kinetics is quite similar in both systems from a technical point of view, but there are major differences in sensitivity. QCM-D systems are more sensitive for water-rich and extended layers, while the SPR system is favored for compact and dense layers. QCM-D, being an acoustic technique, allows measurement of thicker films, while SPR, being an optical technique, has greater limitations concerning the film thickness.
The reason for this difference is due to the different physical principles by which the coupled mass is measured. The mass-uptake estimate from SPR data is based on the difference in refractive index between the adsorbed biomolecules and water displaced by the biomolecules upon adsorption. This means that water associated with the protein film (e.g., the hydration shell) is essentially not included in the mass determination. In contrast, changes in frequency acquired with QCM-D measure water coupled as an inherent mass via direct hydration, viscous drag and/or entrapment in cavities in the adsorbed film. The SPR response is therefore proportional to the coupled ‘molar mass’, while in QCM-D measurements the layer is essentially sensed as a ‘hydrogel’ composed of the macromolecules and coupled water.
However, while SPR measures one parameter only, the additional information contained in energy dissipation data from QCM-D enables a more detailed interpretation. Changes in the dissipation are related to the shear viscous losses induced by the adsorbed layers, and thus provide information that can help the identification of structural differences between different adsorbed systems, or structural changes in the same type of molecule during the adsorption process.
The Q-Sense E-series, Q-Sense E4 and Q-Sense E1 are since feb 2016 called Q-Sense Analyzer and Q-Sense Explorer.
What is the mass sensitivity of Q-Sense instruments?
The maximum mass sensitivity in liquid is about 0.5 ng/cm2 for Q-Sense Pro and Analyzer/Explorer if measuring at a rate of one data point every five seconds. Q-Sense Pro and Analyzer/Explorer operating with four sensors and at three harmonics has a sensitivity of about 2 ng/cm2 if all data are collected in one second. For example, consider a monolayer (<100% surface coverage) of myoglobin (17.8 kDa): the monolayer corresponds to 177 ng/cm2 (change in frequency, 10 Hz).
What is the frequency range of Q-Sense instruments?
The frequency range is 1-70 MHz with Q-Sense Pro and Analyzer/Explorer. A large range is important to be able to use the unique features of multiple frequency and dissipation sampling.
What are the benefits of taking measurements at several frequencies simultaneously?
Simultaneous measurement at multiple overtones is required to model viscoelastic properties and to calculate the correct thickness of films that do not obey the Sauerbrey relation. With the Q-Sense Analyzer system, 14 incoming parameters (seven frequencies and seven dissipation values) per sensor provide a well-determined model of the particular film properties. Moreover, the different overtones give information about the homogeneity of applied layers: as the detection range out from the sensor surface decreases with increasing overtone number, abnormal frequency behavior suggests vertical variations in film properties. The fact that the detection range from the sensor surface decreases with increasing frequency is also used by the modeling software to calculate an accurate thickness of films that do not fully couple to the oscillation of the sensor. For rather soft films, with high water content (e.g., films made of large proteins), you will not obtain accurate thickness information without taking measurements at several frequencies. Another advantage of using higher overtones is the decrease in signal to noise ratio, which is beneficial when extra-high sensitivity is desired.
What is the exact detection range into the medium above the sensor?
The detection range depends on the penetration depth of the oscillatory motion of the liquid/film above the sensor and varies from nanometers to micrometers, depending on the viscoelasticity of the applied film and overtone number. In pure water, the detection range is approximately 250 nm for the fundamental mode. Applying a very rigid film, such as a metal, still allows the same detection range in water. This means that the measurement principle is not affected when a thin film is coated on the surface prior to taking measurements. Compared to optical methods, the detection range of QCM-D is an advantage. Consider, for example, polyelectrolyte multilayers several hundred nanometers thick. These are easily sensed by QCM-D.
See here for more details.
What is the maximum thickness of an applied/adsorbed film?
The maximum thickness of a sensor coating depends on the viscoelasticity of the coating and may vary from a couple of hundred nanometers to a few micrometers. The more rigid the layer, the thicker the layer can be. It is always possible to contact Q-Sense to request new surfaces.
What is the minimum sample volume required for the Q-Sense Pro
The volume in the module above each sensor is 15 µL and the minimum volume required (including inlet and outlet channels) is 50 µL for each sample port.
What is the volume of the measurement chamber and the module as a whole?
The volume on top of the sensor is 40 µL and the total volume inside the module (no tubing included) is 150 µL. This includes the temperature loop going from the inlet to the sensor volume that ensures the liquid that enters the sensor volume has the right temperature.
What is the time resolution?
The maximum rate is up to 200 data points per second, giving you a high-resolution real-time measurement suitable for fast reactions.
What fluids can I use?
Many different fluids including water, inorganic salt solutions, alcohols, and organic media (even e.g., hexane and toluene) can be used. Except for the titanium wall of the chamber, the fluid in the Analyzer, Explorer and Initiator is exposed to tubing and O-rings that can easily be changed for different types of measurements (the so called high resistant kit). In Q-Sense Pro, the fluid is also exposed to the materials in the pumps and the sample probe. For dull details on chemical compatibility, check the manual for your specific instrument or contact support.
Why does the baseline shift when I change buffers?
The resonant frequency and dissipation factors of a QCM-D sensor measuring in a liquid are influenced by the liquid’s density and viscosity. So, if you change buffer from one to another, and the buffers have different viscosities and/or densities, there will be a shift in the f and D baselines. These baseline shifts are often referred to as bulk shifts since they depend on the bulk properties of the liquid.
When, for example, measuring protein adsorption, one can minimize bulk shifts by first obtaining the baseline in the buffer that the proteins are dissolved in. A dilute concentration of, for example, proteins will not significantly change the bulk liquid’s viscosity and density.
If you have a significant bulk shift, you will need to take this into account when analyzing your data. When using QTools, you can compensate for bulk shifts in a measurement if you know how the bulk fluid’s viscosity and/or density change. If you don’t know your test liquids densities and viscosities you can make a QCM-D measurement where you only have a bulk shift and then analyze this with QTools to calculate the change in viscosity or density when going from liquid to another.
What is the temperature range of the Q-Sense Pro?
The working temperature (given normal room temperature) is 4-70 °C with a stability of ± 0.02 K.
What is the temperature range of Q-Sense Analyzer/Exporer?
Proper temperature stabilization and function of the chamber can be obtained at temperatures between 15 °C and 65 °C when the instrument is at normal room temperature around 20 °C. However, the Q-Sense High Temperature Chamber enables temperature control between 4 °C and 150 °C. The stability of the actual temperature is ± 0.02 K at 25 °C.
How accurate is the temperature reading of Q-Sense instruments?
The temperature measured with Q-Sense instruments (shown in QSoft as Tactual) is guaranteed to be within 0.5 °C from the true temperature. In reality, this means that a temperature reading of 25.00 °C may in fact be any value between 24.50 °C and 25.50 °C. Also, there may be a temperature gradient because the temperature sensor is located in the chamber base. Please note that this information does not concern the temperature stability of our instruments, which is ± 0.02 K.
There are eight sensors and four pumps in the Pro. Can these pumps be controlled individually?
Yes, the four pumps are controlled individually which means you can run four completely different experiments with different flow rates, different times, different point of switching sample and so on simultaneously.
Are the cleaning programs for the Pro specific to different applications?
There are different cleaning programs for different samples such as proteins, acids, basic solutions, biological solutions. Note that this is for cleaning of the instrument and not the sensors. The cleaning recommendation for the sensors will be as previously since the sensors are the same.
In the Pro, can sample degassing be done inline or is it done offline?
Sample degassing will have to be done offline. There is no inline degassing.
How does the sample mixing mechanism work in the Pro?
Sample A and B are taken from different vials and dispensed, one by one, into the sample port (the cup). Once there, they are mixed by aspiration and dispensing by the needle.
In the Pro, is the data saved as the experiment script is running—or is the data saved at the end of the experiment?
QSoftOmega will either use a default data file name or ask you for one before a measurement starts (depending on how you set your preferences). Data from the experiment will be saved to this file every ten minutes. When the measurement is finished, all data will be saved to the file. So, in case of say power failure, you will lose no more than 10 minutes of measured data.
Positive f and negative D values—how can that be possible?
Typically, f curves decrease with adsorption and increase with desorption. In contrast, D curves typically increase with adsorption and decrease with desorption. Some reasons why curves would go in opposite directions are:
- The sensor was not clean when the measurement was taken, and some species have been desorbed during the measurement.
- The liquid above the sensor at the end of the measurement (or where the curves cross the baseline) has lower viscosity and/or density compared to at the beginning of the measurement.
- The sensor ‘settles’ during a measurement (more likely in the D300 than in the Explorer, Analyzer, Initiator systems or Pro instruments). This might occur if mounting was not optimal, causing the sensor to shift due to an external force, such as someone tilting the instrument. A solution in this case is to gently tap the chamber or flow module prior to starting data acquisition.
When is it correct to use the Sauerbrey relation to calculate the mass adsorbed on the quartz crystal?
The Sauerbrey relation describes the linear relationship between changes in frequency and changes in mass for thin films adsorbing to the sensor surface. It gives a good estimate of mass/thickness, as long as the dissipation is relatively low. When the dissipation value typically reaches above 1·10-6 per 10 Hz, the film is too soft to function as a fully coupled oscillator—the regions distant from the surface do not couple to the oscillation of the sensor. This means that the Sauerbrey relation, which is normally used to calculate the mass directly from the change in frequency, will underestimate the mass. However, by measuring both dissipation and frequency at several harmonics, it is possible to extract the correct thickness estimations even in these cases. This also makes it possible to calculate the viscoelastic and structural properties using a viscoelastic model incorporated in the Q-Sense software, QTools.
What could be the problem if the instrument does not start?
- Check that the power cord is connected.
- Check that the voltage rating on the back panel of the instrument is properly set for local voltage conditions in the lab. If not, unplug the instrument, open the plastic cover and turn the drum so that the correct voltage appears through the window. Check that the fuse has not blown.
No resonance peaks can be found. What could be the reason?
- The settings to drive the sensor may need to be adjusted if the resonance frequency lies outside the search range specified in the settings. If running QSoft 401, uncheck ‘Automatically optimize all resonances’ in the ‘Find resonances’ window and widen the frequency range under ‘Individual resonance settings’, until a resonance peak is visible. If running QSoft 301, increase the value in the ‘Settings’ › ‘Sensor’ › ‘Search range (± kHz)’ cell.
- The sensor resonance may be dampened too much. The dampening can become too high if the medium in which the sensor is immersed is too viscous or has too high density. A film attached to the sensor can also cause heavy dampening, as can certain defects in the sensor. In this case, the resonance peak in the sweep chart is small and can even be hard to distinguish from the background noise.
- verify that the sensor is installed correctly and/or is not broken;
- check whether a frequency can be found with another clean sensor or ‘Individual resonance settings’ (QSoft 401) or ‘Settings’ › ‘Acquisition’ (QSoft 301). Narrowing the ‘Frequency range’ (QSoft 401) may make the resonance peak more pronounced.
I see small peaks around the large resonance peak while searching for f and D. Could that disturb my measurement?
When searching for the resonances before starting a measurement, smaller resonance peaks may appear around the true overtone modes (mainly seen in air). These unwanted spikes are the result of small deviations in the sensor design (electrode and quartz dimensions, parallelism between interfaces, etc.) and do not normally affect the measurements because they are much weaker than the signals of interest. The only situation where you need to be concerned with the small peaks is when the unwanted modes show equally high peak values as the true one, as the instrument then will have difficulty determining which one to track. If this is the case, damage to the sensor crystal surface will probably be so severe as to be visible to the naked eye. Unwanted modes are much less stable than the true resonance modes, so it should be obvious from drifts and noise if the instrument is tracking the wrong peak.
The fundamental resonance is much less stable than the other resonances. Why?
It is not unusual for the fundamental frequency to be rather unstable. The reasons could be numerous, but the most important one may be that edge effects are much more pronounced for the fundamental tone than for the overtones, since this is the one that reaches the farthest out to the edge of the sensor. As it is sensing almost the entire sensor surface, the fundamental resonance may also be disturbed by the O-rings.
I obtain very regular fluctuations in f and D values. Why?
If symmetric, periodic noise is seen in both frequency and dissipation in any of the overtones when running QSoft 401 on your Analyzer/Explorer, it is most probably caused by an external source.
When both f and D show periodic behavior, the disturbance is probably not caused by temperature fluctuations, as temperature has a much smaller effect on D than on the frequency.
If f and D fluctuations occur while running a peristaltic pump with your instrument, try turning the pump off. It is of great importance to have a pump that does not send pressure waves through the tubing while it is running. A pump with many rotating rollers will give a more stable signal than one with few rollers.
The peristaltic pump that Q-Sense supplies with our instruments does not induce any pulsation or disturbances when it is turned on or off. However, if the inner diameter (ID) of the Teflon® tubing used for connecting the Analyzer or Explorer flow module(s) is too small, the pressure in the flow system will be too low to allow a stable flow, and pulsation behavior may occur. It is recommended to use tubing with an ID of at least 0.75 mm.
The signal does not return to baseline or becomes unstable when rinsing with liquid. What could be the reason?
- There may be bubble formation on the sensor. If bubbles are trapped in the vicinity of the sensor, the measurement signal often does not return to the original baseline after rinsing. Bubbles make the signal unstable. Solution: Avoid the formation of bubbles. This is done by preferably using degassed liquid. Do not insert liquid with a temperature below the working temperature of the measurement chamber, as dissolved gas can be released during heating.
- Contaminants in the sample liquid can induce instability. Check the quality of the samples.
- The sensor may be experiencing a ‘pressure shock’. Irreproducible jumps in f and D can occur if the sensor is mechanically stressed by increasing the pressure on one side of the sensor when fluid is forced through the measurement chamber. Solution: Try to use lower pump flow rates.
- The sensor may be experiencing a ‘temperature shock’. Irreproducible jumps in f and D can occur if the sensor is thermally shocked, i.e., rapidly changing the temperature of the sensor. Solution: Make sure to keep sample solutions at roughly the same temperature as the Set temperature. Also, keep in mind that the larger the temperature difference between the sample and the set temperature, the slower flow speed needs to be used in order for the sample temperature to reach equilibration before it reaches the sensor.
The measurement shows excessive noise. What could be the reason?
- Check that the sensor is mounted correctly with the arrow-shaped electrode towards the mark on the sensor holder (to the left). See sub Chapter ‘Mounting the Sensor Crystal’ in the Operator Manual. If the sensor is mounted in the wrong direction, the grounding of the electrodes will not be optimal, and current leakage may interfere with the measurement.
- If the sensor has scratches or damage on its surface, this may give rise to unwanted disturbing resonance peaks, seen adjacent to the true resonance peak in the frequency sweep window. If these unwanted modes are of the same amplitude as the true one, the instrument may jump over and follow them instead. If a false or non-pure resonance peak is followed, it could result in high noise.
- A sensor loaded with an inhomogeneous coating or a coating with high surface roughness could also give rise to non-pure resonance peaks and thus higher noise.
- Check for bubbles, or if measuring in air, residual liquid on the sensor or in the flow module/chamber.
Why does the frequency shift when I expose the surface to (UV) light?
It is very difficult to avoid temperature effects when working with (UV) light exposure. Even though the quartz itself is transparent in the UV-spectrum, the sensor electrodes are generally not. All the light an electrode will absorb is converted into heat. As a consequence, this will in many cases induce stresses in the electrode (generally, a material expands when heated) that will be transmitted to the underlying quartz. The resonance frequency will change as a consequence. The dissipation factor is usually not affected by these stresses. However, if you turn on the UV light in water you could see a shift in dissipation due to the heating of the water and hence a change in the water’s viscosity and density.
I find liquid outside the sensor area after opening the flow module/chamber. What could be the reason?
Liquid on the backside (the ‘anchor side’) of the sensor can cause a lot of problems for QCM-D measurements. If the backside of the sensor is facing any droplets of liquid, slow humidity stabilization processes will affect the f and D baselines, and destroy any attempt to make quantitative measurements. For prevention:
- Check that the sensor does not have any cracks or notches at the edges. Such damage may reduce the sealing capability of the O-ring.
- Check that the sensor is centered over the O-ring.
- For Analyzer/Explorer, check that the tubing connections are tight. Is there any liquid outside the black nut? It is very important that the Teflon® tubing is cut off at exactly 90° to ensure proper sealing. It is recommended to use the tubing cutter included in the Liquid Handling Set.
What is the angle of incidence for the ellipsometry module?
The angle of incidence for the ellipsometry module is 65°, and this equals the angle of reflection.
What setup is required for the ellipsometry module?
Note that the ellipsometry module can only be used with Q-Sense Explorer chamber platform, as you need optical access from both ends of the module and the design of the Analyzer chamber platform does not allow for this. Q-Sense does not recommend any particular ellipsometer but there are two suppliers that we know are compatible with our ellipsometry module and have a table especially designed to fit the Explorer chamber: Woollam and Accurion.
What is the maximum working temperature for the electrochemistry module?
The electrochemical module can withstand a maximum of 40 °C, which is limited by the reference electrode.
Which external factors might affect the resonance frequency and dissipation shifts?
The crystal may react to other things beside surface interactions:
- Temperature changes/stresses.
- Pressure changes/mounting stresses.
- Pressure waves.
What is the highest viscosity that can be measured with QCM-D?
We have measured an upper viscosity limit to 47 cP for a liquid of density 1204 kg/m3. The response will be also affected by density. In addition a maximum damping of ΔD ~2500E-6 has been measured. Higher damping hinders the oscillation of the sensor.
What microscope objectives can be used with the window module?
Two basic requirements have to be fulfilled:
- There must be enough room on the bench of the microscope to fit the chamber there.
- The focal distance of the objective lens has to be long enough to reach the sensor surface.
Our window module has a glass slide thickness of 1 mm and the distance between glass and sensor surface is another 1 mm, which gives a total distance of 2 mm down to the sensor surface.
What is the difference between measuring resistance and energy dissipation?
In order to completely describe the viscoelastic properties of a film adhered to a QCM sensor, it is necessary to measure all sources of energy losses or damping for the oscillation. Energy dissipation, D measurement as with QCM-D is the most direct way, but impedance measurements also obtain the full information on viscoelastic properties of the film. Resistance, R is only part of the impedance and thus cannot be directly correlated to viscoelastic properties of the film. To obtain complete information, capacitance measurement is also necessary, and it is possible to have a situation where resistance is not changed but where capacitance does change, or vice versa and thus changes in viscoelastic properties are missed or at least proportionally wrong. Another consequence of only measuring resistance is that it is not possible to quantify and also relative comparisons between measurements of R is of limited value.
Where is the temperature measured in the Analyzer instrument?
The temperature is measured immediately below the flow modules, in the center of the contact block on the chamber platform. Firm contact between the modules and the platform allows for good thermal conduction, so as soon as all curves (temp, f, and D) are stable, you know that the temperature has equilibrated to Tset over the sensor surface.
What is the maximum rate for temperature ramping on the E4/E1?
The typical maximum rate for the temperature programming in QSoft 401 is 0.5 K/minute, if the temperature control has enough time to adjust. It depends on how many flow modules are used and at which temperatures you are working. Quicker ramps will give larger over- or undershoots, so it is up to the user to determine if this is critical or not.
What is the Reynolds numbers for the flow module in the E4/E1?
The geometry of the flow module is complex to describe, with its beveled ceiling (the surface across the sensor surface); therefore, the Reynolds numbers are estimated. Assuming that the inner volume is a rectangular ‘pipe’ of 0.7×12 mm, the Reynolds number at 100 µL/min is 0.2, and at 800 µL/min, 2.0. Generally, a Reynolds number below 2300 is associated with a laminar flow, which means the flow through the E-Series Flow Module is well within the boundaries.
What is the power consumption of the E4 instrument?
When 240 V/50 Hz is used, between 105 VA and 123 VA have been measured. When the temperature reaches the set value, the consumption decreases somewhat.
What are the inner dimensions of the E4/E1 flow module?
The inner diameter of the O-ring is 11.1 mm; the distance between the sensor and the ceiling of the cell is 0.6 mm in the centre; the heat exchanger has a cross-section of 0.8×1.0 mm; the holes in the cell ceiling where the liquid enters to the sensor are 1.0 mm in diameter; the tubing is 0.75 mm in diameter.
There is no connection with the instrument (E4/E1). What could be the problem?
- Check that the USB cable is plugged into the PC and the instrument.
- Check if the hardware ‘Q-Sense E-Series Device’ is found and installed on your computer. If not, open the installation file found in the C: directory under Program Files/Q-Sense/QSoft 401. Follow the instructions (see also sub Chapter ‘Installing Software’). The software should be installed before the instrument is started for the first time.
What is the drive amplitude/voltage?
The drive amplitude, as used in QSoftPro and QSoft401, relates to the amplitude of the drive voltage over the sensor.
You can set it under ‘Individual resonance settings’, the settings tab that appears if the tickbox ‘Automatically optimize all resonances’ is unchecked. This value is proportional to the output voltage from the electronics unit. However, the actual voltage over the sensor depends on how loaded (dampened) is since there are capacitive losses in the transmission lines to the senor. So it is not possible to give an exact relationship between the value set in QSoft and the voltage over the sensor. Around 50 mV in air and 1 V in water are typical values over the sensor.
Can you calibrate the temperature in the E4 instrument?
Yes. In QSoft, before you start a measurement, go to the ‘Tools’ menu, then select ‘Show Pre-Acquisition Form’. Select the desired ‘Set Temp’ and allow the ‘Tact’ to stabilize for at least 2 minutes.
Thereafter, under ‘Tools’, select ‘Calibrate Set vs Actual Temp’, and click ‘Apply’. The ‘Set temp’ line should adjust to the ‘Actual temp’. Normally this is done at 25 °C, but it can be done anywhere between 15 °C up to 50 °C.
The resonance frequency is lost, resulting in the error message ‘Warning: bad fitting of the decay curve’. Why is this?
- The environment of the sensor may be changing very fast, so that the changes in frequency and dissipation cannot be tracked effectively. Solution: Increase the data acquisition speed. Optimal speed is obtained by changing the settings under ‘Resonance optimization’ in the ‘Find resonances’ window. Move the pin towards ‘High speed’.
- The sensor has been loaded more and more during data acquisition and at some point the sensor cannot be loaded further as the dampening becomes too high. Solution: In some cases, the sensor can still be forced to resonate by optimizing the settings for acquisition. Check the effect of changing ‘Drive amplitude’ under ‘Individual resonance settings’.
What parts are needed to convert the E4 system to high chemical resistance?
- (QCS033) High Resistance Sealing Kit E4, 4 Kalrez O-rings, 4 Kalrez gaskets, 4 GORE® Style 100CR tubing for IPN-N4, 4 Perifits.
Is it possible to run my experiments in toluene or similar harsh solvents?
Yes, then you need to use the GORE® tubing:
- QCS 032 Pump Tubing GORE® Style 100CR highly resistant for IPC N4 (1 pc)
Note: should be used together with perifit QCS 035
- QCS 035 Perifit PEEK for QCS 032 Pump Tubing GORE® Style 100 CR, (1 pc)
Or you can buy a high resistance kit containing both O-rings, sealing gaskets and two pieces of GORE® tubing:
- QCS 033 High Resistance Sealing Kit E4, (4 Kalrez® O-rings, 4 Kalrez® gaskets, 4 GORE® Style 100 CR tubing for IPC-N4, 4 Perifits)
If I want to run my experiments with ethanol, what should I keep in mind?
For measurements in ethanol we recommend that you use Kalrez O-rings and sealing gaskets as the standard Viton material might swell:
- QCS 017 O-rings for QFM 401, Highly Resistant (Kalrez® 11.1×1.6 mm, 4 pcs)
- QCS 018 Sealing for QFM 401, Highly Resistant (Kalrez®, 4 pcs)
The pump tubing needs to be exchanged as well. For ethanol, the MHSL Tygon tubing is suitable:
- QCS 031 Pump Tubing Tygon MHSL (e.g. ethanol resistant) for Ismatec IPC-N4 (6 pcs)
What is the volume of the open module?
The maximum volume (of the outer Teflon® container) is roughly 2.5 mL. However, we do not recommend that you use the open module with larger volumes than 400 mL. The smallest volume (depending on the viscosity of the bulk liquid) is 30–50 mL.
Is it possible to store the reference electrode, QSP 020, for the electrochemistry module in ethanol or distilled water?
The Dri-Ref-2SH should not be stored in either of the fluids, because they will damage the electrode. It should only be stored in 3 M KCL solution. This is the same solution that is used to fill the electrode, and as such it provides an isotonic environment for the electrode, which keeps the porous membrane properly conditioned.
The electrode was designed for use in physiological solutions. It is not known how well the electrode functions as a reference in an ethanol environment.
What are the materials and chemical compatibilities of the tubing ferrules and nuts?
The ferrules are made of chlorotrifluoroethylene (CTFE), which is very resistant to most chemicals, except THF and some halogenated solvents. It is resistant to all inorganic corrosive liquids (acids included) but swells in ketones.
The nuts are made of polyphenylene sulphide (PPS), which is very resistant to all solvents, acids and bases.
What is the surface roughness of the sensors?
Q-Sense sensors are optically polished and have a surface roughness of <3 nm, RMS. All other coatings are added on top of the Au layer, which means that the surface roughness of other materials is equal or slightly larger than 3 nm RMS.
What is the active area of the sensor for each different overtone?
The sensitivity distribution becomes narrower for higher overtones. The distribution is Gaussian and approaches zero at the edges in an asymptotic way. It is therefore difficult to discuss active area and sensitivity dependence on radius/surface of the sensor. In addition, all calculations in QSoft and QTools assume that the complete surface is covered or at least homogeneously covered and any calculations should therefore be done over the whole surface.
What coatings/surfaces can be used?
The sensor can be coated with almost any material, as long as it can be applied as a thin (nm range), homogenous layer firmly attached to the underlying surface. The layer thickness can vary between nanometers and micrometers, depending on the viscoelastic properties of the applied material. Q-Sense offers pre-coated sensors with e.g., gold, Ti, SiO2, AlO3, stainless steel, hydroxyapatite, polystyrene and biotin. Several other materials are also available, e.g., most metals, metal oxides or spin-coated polymers.
When is the adsorption layer considered as rigid enough for the Sauerbrey relation to be valid?
The layer is rigid enough when the overtones overlap. If they start to deviate, it is up to the user to determine if the mass estimate with the Sauerbrey relation will be a sufficient approximation. This can be done by comparing the Sauerbrey masses calculated using the lowest and highest harmonic, respectively.
What is the maximum thickness of a polymer layer that can be coated on a gold sensor without affecting its performance?
Maximum possible thickness very much depends on the viscoelastic properties of the polymer in question. With a very viscous polymer such as silicone it can be hard to oscillate the sensor already at a thickness of 1 micron. However, for a stiffer polymer it might work with a several microns thick adlayer. For example, up to 10 microns thick polystyrene adlayers have been used with a still functioning sensor. But generally—the thinner, the better!
One of my sensors shows higher dissipation values than the other, what could be the reason for that?
The reason why one sensor has higher absolute dissipation than others is most likely not due to roughness. The absolute D can be a little higher than normal due to how various resonance modes couple in the crystal, which in turn depends on crystallographic defects and small variations polishing that give small geometrical effects. All sensors have many vibrational modes that you see as peaks on the plot when QSoft sweeps the frequency as it is finding the main resonance peak. If one of these other modes are close to the main mode, this drains energy from the main mode and hence a results in higher dissipation. However, since you are measuring dissipation shifts, this normally does not influence your measurement. However, if the coupling is too large, you will see this as an increase in noise and drift since the other modes are not as stable as the main mode.
If a small notch is introduced to the sensor edge during handling, how will it influence the performance?
This depends on the size and location of the notch. First, it must be small enough so the seal at the O-ring remains intact (approximately 1.6 mm/1 mm thickness for standard and other modules respectively). Secondly, it should not affect the electrodes. We cannot guarantee a good performance if this is the case but it might still be possible to use it with good results. You are recommended to ensure that the resonance peaks can be found with normal dissipation values, in which case the sensor can be used without problem.
Should the chamber be empty or filled with water or buffer when finding the initial resonance frequencies?
It is good, but not necessary, to check the resonances in air to make sure that they look good. One can routinely check the resonances in air before introducing the fluid in the modules.
Is it possible to clean polystyrene (PS) surfaces with ethanol?
Yes. Ethanol can be used to clean polystyrene.
What are the pH limits for the hydroxyapatite (HA) sensor?
The lower limit for hydroxyapatite is between pH 5 and 5.5. Below this, HA starts to alter and dissolve. Basic solutions should be no problem.
Is it possible to clean the hydroxyapatite (HA) sensors with SDS?
Cleaning hydroxyapatite sensors (QSX 327) with SDS may leave residues on the surface.
What problems could arise when using SDS?
SDS in an anionic detergent and should not adsorb to negatively charged surfaces such as SiO2. However, one thing to consider is that SDS hydrolyzes with time, forming a hydrophobic product (a phase change in the SDS solution) that might act as a contaminant on the surface. So, to be on the safe side, fresh SDS solutions should be used if the surface cleaning is performed in situ.
UV/ozone treatment after SDS will remove these residues.
How does heating affect the sensors?
Heating will influence the sensors, but the extent depends on temperature, exposure time and type of sensor.
At 573 °C the quartz undergoes a transition from a to b phase, which alters its piezoelectric properties. Both the quartz and the Au coating withstand temperatures below this point, however the adhesion layer (Cr) is known to migrate in Au, and the migration rate is affected both by temperature and time. We have verified that 500 °C for 5 minutes is okay for the QSX301. However, we cannot guarantee the performance of any additional coating outside the standard working temperature range of the E-Series (15-65 °C).
Significant Cr migration has been seen at annealing temperatures of 250 °C and 450 °C for periods of 0.5-22 h. So either lower temperature for longer times or high temperature for shorter time would be recommended.
For coated sensors (i.e. all but QSX 301), an additional adhesion layer and the coating material has to be taken into account, which makes it even more complex.
What is the reason for the overtone spread in the case of a soft adlayer?
The resonance frequency of the sensor is a function of the motion of the sound wave in the sensor and out in the layer on top of the sensor (attached molecules and liquid medium). If the layer on top of the sensor surface (for example a layer of adsorbed molecules) is very thin and rigid it will move in phase with the sensor and the influence of this layer on the motion of the sensor will be negligible. In this case all overtones will give the same response and the Sauerbrey equation is valid. If an attached layer is soft it will not move entirely in phase with the sensor and this will influence and dampen the motion of the sensor. The amount of dampening is a function of the viscoelastic properties of the attached layer. Also, since each overtone makes the sensor move in a different way, the viscoelasticity influences each overtone in a different way. This is the reason of the spreading of the overtones in the case of a soft layer.
After careful cleaning and finding resonances, I found one of the overtones has a double peak. Can I use just the remaining overtones to analyze the data?
There should be no double peaks at any harmonic. By double peaks one means two peaks that are of the similar height and the width of the peaks are partially overlapping. If one peak is a lot higher than the other, the measurement will work just fine anyway. In order to analyze data with QTools, at least two harmonics are needed. So, not using one of the overtones will be okay.
Is it possible to measure the thickness and mass of an ex situ deposited coating using QCM-D?
It is common to coat the QCM-D sensors ex situ by immersing into different coating solutions outside the measurement chamber. One can then get a rough mass estimation by first acquiring a baseline of the uncoated sensor in air and then stitching the file in QSoft (open both files in QSoft and go to ‘File’ › ‘Stitch data file’) with the baseline from the coated sensor in air.
Please note that the error can be quite large since placing the sensor differently onto the O-ring each time might give different frequency changes. It is still possible to get a rough idea of the adsorbed mass, but it is important to be careful and repeat the experiment with different sensors and calculate a mean ± SD. After immersion it is also important to remove residues from the counter gold electrode before remounting into the QCM-D flow module.
My sensor has a very high D value—can I still use it?
- The absolute D can be a little higher than normal due to how various resonance modes couple in the quartz crystal, which in turn depends on crystallographic defects and small variations in polishing that give small surface effects. All sensors have many vibrational modes which you see as spur peaks that are plotted when QSoft sweeps the frequency as it is finding the main resonance peak. If one of these other modes is close to the main mode, this drains energy from the main mode and hence there is higher dissipation. However, since you are measuring dissipation shifts (rather than absolute values), this normally does not influence your measurement. If the coupling is too large, you would see this as an increase in noise and drift because the other modes are not as stable as the main mode. Note that a chipped sensor can give spur peaks.
- An incorrectly mounted sensor can cause a higher D-value. Check that the O-ring is lying flat in its bed, and that the sensor is centered over the O-ring.
How large is the sensor area?
The standard sensor has a diameter of 14 mm. Because the sensor is most sensitive in the center, it is important to ensure that the same reaction is taking place over the entire surface in order to compare measurements, i.e., that your sample forms a homogeneous film.
How many times can the sensor crystal be reused?
This depends on the application and the possibility of cleaning the sensor. If only mild cleaning conditions are needed and the application is insensitive to increased surface roughness, a sensor can be used for numerous experiments. However, for certain applications a standard surface can be used only once.
Why is there a notch in the sensor crystal?
The notch depicts the x-axis of quartz crystal, which is the direction of oscillation. The x-axis is perpendicular to the flat part of the notch.
Are there any out-of-plane movements when the sensor crystal is oscillating?
The sensor oscillates in thickness shear mode, which means that the movement is in-plane. Ideally, this would be the only motion, but it is not possible to totally eliminate out-of-plane oscillation (flexure mode)*. In liquid, this mode causes pressure waves to occur that can disturb the normal oscillation. The fundamental 5 MHz oscillation is most perceptible to this disturbance.
*If you fix a rubber band between two points and then pinch it in the middle and move the center towards one side you will see how the band gets thinner on one side and buckles on the other. The same thing happens with the sensor (but on a much, much smaller scale) when it oscillates since the oscillation amplitude is larger in the center of the sensor than at the edges.
Is it possible to compress the QSD data files?
Yes, you can make the data files smaller (for details, see the User Manuals):
- Before a measurement: In the ‘Setup Measurement’ menu, under ‘Resonance optimization’, you can vary the time resolution by sliding the pin on the dial towards low noise, i.e. low time resolution.
- After a measurement: In the ‘File’ menu, there is a function ‘Condense…’ with which you can compress the QSoft data. The output file will be a QTools data file.
- Before a measurement: In the ‘Settings’ window, under the tab ‘Miscellaneous’, there is a line ‘Points in median’ where you can set, for instance, 10 which would mean that 10 data points are averaged before being plotted on the screen. The whole data set will then be a 1/10 of the size it would have as un-averaged.
- After a measurement: Go to the QSoft directory, found under Program FilesQ-Sense, and open the .exe file ‘Condenser’. Follow the instructions from there.
How do I stitch files?
- Open QSoft 401 (does not work in older versions).
- Open the two files that you would like to stitch.
- Go to ‘File’ › ‘Stitch data files’.
- A new window appears. Here, you choose which of the two open files that should come first. You should choose the file for the baseline of the bare surface. You also have an option to choose the ‘new time between data files’. Set this time to ‘0’ (i.e. there should be no time difference between the two files).
- Click ‘Stitch’.
How do I install and activate the QTools software?
- Please exit all programs before attempting installation. QTools can be found either on the installation CD or at our website.
- Run the QTools installation file and the InstallAware wizard will guide you through the setup process. Please note that you need to have admin rights in order to be able to complete the installation.
- If QTools has not been previously installed on this PC, the QTools installation manager will automatically be launched the first time you start QTools. You can then start a 10-day trial period. We recommend that you at this time apply for a registration string. Just follow the on-screen instructions.
There are two types of registration strings, temporary and permanent. A temporary string is 25 characters long and will expire in a few days. A permanent string is 30 characters long and can only be obtained after you have sent the file ‘QTools reg info.qri’ (from the folder specified in the information dialog box that QTools presents – depends on the OS) to email@example.com. This file will automatically be generated by the QTools registration manager. If you have an email program running, QTools can automatically use this to create an email. All you then have to do is to click on ‘Send’ in the mail QTools created for you.
The ‘QTools reg info.qri’ file contains information that identifies your computer and this information will be coded into the registration file you will receive from Q-Sense. QTools will periodically check if there is a match between the registration string and the ‘QTools reg info.qri’ file. If there is no match, QTools will notify the user and ask for a valid registration string. QTools cannot be run from a local server but needs to be installed locally on each computer.
Please also note that after changing hard drive or upgrading from Windows XP to 7, a new QTools registration string needs to be generated after software reinstallation.
How do I register QTools if it is installed on a computer without an Internet connection?
- First locate the registration file named ‘QTools reg info.qri’ from the folder specified in the information dialog box that QTools presents during registration (folder depends on the OS).
- Copy the file to another media (thumb drive), then send that file as an attachment from an Internet connected PC with an email client.
Please note that it is preferable to identify this file with a name chosen so that it is possible to know which PC it came from. The reason is that each registration file is unique. It is especially important if there are several QTools computers in the facility.
How do I deactivate my QTools registration string to allow a new user to install QTools?
Open QTools. Go to ‘Help’ › ‘Launch Registration Manager’, then click ‘Remove registration’. This will disable QTools on that computer. Note that the registration string is connected to the computer and not the user. Also, it is necessary to have administrative rights in order to run QTools registration manager. QTools, however, can be run under normal user rights.
The new user can then apply for a new registration string on another computer. For details see the FAQ ‘How do I install and activate the QTools software?’.
What is the maximum kinetic resolution of Analyzer/Explorer?
The maximum acquisition rate is more than 200 data points per second. If default settings are used, an average function is employed that gives around 100 data points per second, distributed according to how many modules and frequencies that you have chosen to acquire. The exact number of data points taken depends on how fast the signal is damped, which means that a measurement in water gives a higher kinetic resolution than one in air, and higher frequencies give a higher resolution than lower ones.
Why does the number of data points per time unit differ within one single measurement?
QSoft is trying to sample as many points as possible with the given settings (more resonances and more averaging will slow down sample speed). For each point, a lot of data is being transferred from electronics to the PC, where it is processed. So depending on how much the PC is loaded with other processes it will have a slightly different sampling speed.
Why are the default settings in QSoft 401 different for different sensors?
Clicking ‘Automatically optimize all resonances’ will give the default settings for a measurement run. The optimization of driving and recording of the crystal is dependent on D and the overtone number, which means that different sensors (flow modules) can have different settings.
How do I handle the error message ‘Instrument running uncalibrated’?
Make sure you have got the latest version of QSoft401 installed. This version of the software will take care of the problem automatically or guide you through the steps necessary to solve it.
I am using solvents with my D300, but the QSoft settings only refer to water or air. What settings should I use for solvents?
There are no particular settings for each type of solvent, such as toluene or ethanol, but they should be similar to water settings. What is important is that the decay curve window looks normal, i.e. the time interval used for data sampling of the sinusoidal decay curve is properly chosen: it should be long enough to include a sufficient number of oscillation periods, allowing a good mathematical fit to it, but not too long so that the decay curve has leveled out within the window. Use the ‘Sample frequency’ to change the length of the decay curve capturing window.
See here for examples.
What is ‘wavelength’ in QSoft 301?
The wavelength, set under ‘Settings’ › ‘Edit…’ › ‘Acquisition’, is the number of data points used in the fitting of a decay curve. Together with the sampling frequency they give the decay fitting time.
See here for details.
What is the OS compatiblity for QSoft and QTools?
QSoft and QTools are compatible with Windows 7, Vista, XP and Windows 10 platforms. Please note that you need a native Windows installation (it will not work properly on virtual Windows for e.g. Mac).
Can I install QSoft or QTools on a Mac?
There is currently no version of QTools for the Mac OS. It may be possible to install it on a dual boot Mac, with Windows XP or higher installed on it. QTools cannot be registered on Windows emulation software made for the Mac OS, however. You will need to partition your hard disk, then install a licensed copy of Windows on it.
Why are only odd harmonics being measured?
- This has to do with wave physics in that a QCM cannot resonate at the 2nd, 4th and 6th (etc.) multiples of a half wavelength that defines the fundamental tone and that depend on the thickness of the crystal. In theory, there are also resonances at these even multiples of the eigen frequency (the fundamental tone) but they can only be excited mechanically, and would only have an amplitude inside of the quartz, and therefore meaningless as we want to study what is happening on the surface of the quartz. This is why it would be wrong to say that we use the 1st, 2nd, and 3rd resonances referring to 5, 15, and 25 MHz, and that is why we refer to the 3rd, 5th, and 7th overtones (or harmonics) of the crystal.
- It is a question of physics—the even overtone resonances have a node on both surfaces, and for the QCM to be able to excite oscillation/standing wave at resonance it requires a node on one surface and an anti-node on the other. A QCM can only oscillate at half-wavelengths: the fundamental tone has a wavelength twice that of the thickness of the crystal, thus a node on one surface and an anti-node on the other. The third overtone has a wavelength a third of the fundamental tone, thus having a node on one surface, a node two-thirds of the way through the crystal and an anti-node on the other surface. The fifth overtone has a wavelength one fifth of the fundamental tone, thus a node on one surface and two nodes inside the crystal (at 2/5 and 4/5 of the thickness of the crystal) and an antinode on the other surface.
What is ‘buffer effect’?
Since the technique is sensitive to any change in the medium above the sensor surface, a shift between two buffers will affect the measurement. The easiest way to identify them is that they occur instantaneously, in contrast to most adsorption processes that take place more slowly. A ‘buffer step’ is recognized as instantaneous, reversible and surface independent.
The best way to avoid buffer steps is to keep the concentration of the analytes down and, of course, to use the same buffer as much as possible throughout the experiment. Also, if you can do a final rinse with the ‘baseline buffer’ after a completed measurement you will be certain that no buffer effect will disturb the interpretation. Then any jump in f and D due to buffer changes will have returned to their original levels.
Factors such as salt concentration and pH will immediately change the baselines. The effect also occurs if very high concentrations of analytes (e.g. proteins) are used alternately with low ones.
Buffer effects may occur together with surface-related (wanted) effects. It is therefore recommended to always return to the original buffer after finished analyte/sample experiment steps to read off the true signals. Alternatively, a reference measurement with buffers alone can be made first, and the values subtracted afterwards from the analyte results (changes in f and D due to surface related effects and bulk effects are usually additive).
My baselines are drifting—why?
A clean system normally shows stability, with as little as 1 Hz variation per hour on an E4 system and less than 0.5 Hz per hour on a D300 system. If drifts occur, there can be several possible causes. See below for details.
There can be many different causes for drifts in f and D. Following here is a list of possible causes, and suggestions for solutions.
|If a tube is leaking, or the sensor is not properly mounted (or even cracked) this can cause liquid to enter spaces in the measurement chamber where it should not be. For example if the back side of the sensor becomes exposed to only small amounts of liquids or vapors large changes in f and D may occur. Also, if liquids enter the electrical parts of the measurement chamber large variations in the measured signal may result.||Eliminate leaks. Check for leaks by mounting a sensor in a dry measurement module. Close the outlet tube by clamping it. Then fill a syringe with air and connect it to an inlet tube. Press gently for about 30 seconds and then release. You have a leak if the syringe does not return to the initial state.|
|Gas bubbles may form on the surface of the sensor if you use a liquid that is not properly degassed. Such bubbles will of course influence f and D. For example, the gas solubility of water decreases when the temperature is increased. If water with a lower temperature than the measurement chamber is injected then there is a large risk for formation of bubbles.
Note that the risk for bubble formation generally increases with decreasing salt concentration of a water solution.
|Use only degassed liquids or make sure that the gas solubility of the liquid is not lowered during the measurement.
Bubbles can often be removed by using high flow speed of the pump.
|The measurement chamber is temperature stabilized but large variations in the environment may not be fully compensated. Temperature changes will change the viscosity and density of a liquid and thereby change f and D.
Large temperature changes of the electronics unit will also change the frequency of the reference clock. This will directly change the measured frequency (but not dissipation).
At certain temperatures the resonant modes may coincide with unwanted modes that are very temperature dependent. If measuring at such a point, the signal may be affected and drifts occur.
|Make sure the temperature controller is turned on!
Keep a constant environment around the measurement chamber and the electronics unit. Make sure air circulation is adequate and constant around the measurement chamber and electronics unit.
Avoid direct sunshine and air-streams (e.g., from an air-conditioner) to be pointed directly at the instrument.
Change the temperature slightly to ‘come loose’ from the mode intersection.
|The QCM-D is designed to measure surface reactions. However, sometimes there are reactions going on that the user does not anticipate. For example, on a bare gold sensor in contact with water there may be a slow change of the ion content in the Helmholtz double layer. There might also be a slow transfer of contaminants from the module walls to the sensor surface. Or there might be a slow desorption, degradation, or restructuring of the surface layer on the sensor. It is also not uncommon that, e.g., a sensor with a polymer coating absorbs or desorbs solvents or even water that will change the measured mass.
These kinds of ‘drifts’ often induce relatively larger shifts in f than in D (just like most measurements of very thin films do). The frequency ‘drifts’ then follow the mass sensitivities of the overtones, i.e., the shifts in frequency goes as 1:3:5:7 for the fundamental and the 3rd, 5th, and 7th overtones.
|This is not really a drift since it is a result of surface processes, which the QCM-D is designed to measure. You can check if some kind of surface process is the cause of the ‘drift’ by passivating the sensor surface. We have found that passivation of the sensor by lipid layers, proteins, or thiols have significantly reduced these kinds of ‘drifts’.
It is also important to thoroughly clean all parts of the module regularly. It may be necessary to exchange all tubing and the O-ring for new ones.
|(D300) If you have evaporation from the end of the outlet tube and the tube is hanging down, then the pressure on the crystal will change as the liquid level changes. You can easily test how much this pressure changes f and D by starting a measurement in liquid and then slowly move the end of the outlet tube up and down.
The same thing can happen if the valve into the sensor is slowly leaking. Then the pressure (and possibly the temperature) can slowly change causing a drift.
|Keep the outlet tube firmly in place and not allowed to move around. Ideally, the last stretch of the outlet tube is horizontal. Then a small evaporation from the end of the tube will not change the water level and hence not the pressure felt by the sensor. It is also possible to put a valve at the end of the tube which stops evaporation altogether.|
|Most physical stresses on the sensor influence all resonant frequencies and dissipation factors even if the effects are usually more pronounced in the fundamental mode than the overtones. Mounting the sensor in a module will inevitably induce sensor stresses since the O-ring, Teflon® ring (D300) and the spring-loaded gold contacts all exert a force on the sensor. If these forces are held absolutely constant during the run of the measurement, they will usually not cause a problem.
Any changes in these stresses will, however, more or less, induce changes in f and D. For example, if the sensor is unevenly placed on the O-ring there might be a slow creep in the O-ring that will change the mounting stresses.
Also, changes in temperature will change the diameter and elastic properties of the O-ring as well as the dimensions of the measurement module by tiny amounts. This may be enough to significantly chance the mounting stresses.
|Be careful when mounting the sensor to make sure it is placed evenly and centered on the O-ring. Make sure the O-ring sensor, and Teflon ring (D300) are clean and free from dust particles. Stresses can sometimes be released by knocking hard with one finger on the measurement chamber (D300).|
|The backside of the sensor is as sensitive to surface reactions as the front side. If, for example, there is a large change in humidity on the backside of the sensor due to leaks or a large change in temperature, the amount of adsorbed water will change and thereby influence f and D. Note that the air at the backside of the sensor is in contact with the ambient through a small whole. The reason for this small whole is to prevent pressure changes (see Pressure changes above) when the temperature of the measurement chamber is changed.||Make sure the dew point of the air around the measurement chamber (which is in contact with the backside of the sensor) is significantly higher than the measurement temperature. See also Leaks above.|
|Upon changing from working in one solvent to another the O-ring might swell/de-swell due to the changed properties of the liquid (see also Mounting stresses above).||Use different O-rings for different solvents, or pre-soak for long time when changing from one liquid to another.|
Bad electrical contact
|The measured dissipation factor will increase if there is a bad electrical contact (high electrical resistance) between the sensor and the gold contacts. This will increase noise and possibly also drifts. Indicative of this problem is that a clean sensor has a high dissipation factor (>40·10-6) when measured in air.||Make sure the sensor is properly mounted so that the gold contacts will make good contact with the sensor electrodes. Look in the manual if you are unsure how the sensor should be mounted.
It is important that the backside electrodes are clean. This can be a problem if the front side of the sensor has been spin coated with a non-conducting layer, which easily can spill over the edge of the sensor.
Make sure the spring-loaded gold contacts are undamaged.
How does the Sauerbrey equation read?
The Sauerbrey model describes the linear relationship between frequency shifts and mass changes for thin films.
For a detailed description of the Sauerbrey model, see here.
When do I need to use the viscoelastic (Voigt) model?
The simple answer is—as soon as D is larger than zero. Theoretically, as soon as there is any viscoelastic behavior in the adsorbed layers, the mass will not couple 100% to the oscillatory motion of the sensor, and the true mass will be underestimated if the Sauerbrey equation is being used. Putting it the opposite way: as soon as you are able to obtain a stable fit to your data set, it is never wrong to model it. Practically speaking though, it is obvious that small values of D still hold for as a rigid film, especially if the D/f ratio still is very small (for instance, 1:30 or above).
What is the difference between Voigt and Maxwell? What are their respective applications?
Viscoelastic behavior of polymers and other materials are often simulated using elastic springs and viscous dashpots. The Maxwell model is the simplest model for a more liquid-like viscoelastic soft matter material and it consists of a spring and dashpot in series. The Voigt model is the simplest model for a more rigid viscoelastic soft matter material and it consists of a spring and dashpot in parallel.
A detailed description, including the equations, of the implemented models can be found in M. V. Voinova, M. Rodahl, M. Jonson and B. Kasemo ‘Viscoelastic Acoustic Response of Layered Polymer Films at Fluid-Solid Interfaces: Continuum Mechanics Approach’, Physica Scripta 59 (1999) 391-396.
Can I model a Newtonian fluid?
Yes, you can model either the density OR the viscosity of a Newtonian fluid. It is not possible through modeling to separate the density and viscosity of a Newtonian fluid. You need to know either one or the other. The frequency and dissipation response going from vacuum to such a fluid depends only on the density × viscosity product. So you need to fix one of the parameters in order to get the other.
Can I get both viscosity and density of a Newtonian fluid through modeling?
It is not possible by modeling to separate viscosity and density of a Newtonian fluid. The frequency and dissipation response going from vacuum to such a fluid depends only on the viscosity × density product. You need one of the parameters in order to get the other.
How do I work with fixed versus fitted parameters?
Under the tab ‘Parameters’ you can choose to fit the parameters, or to use them as fixed values in order to help determining other fitted parameters. By double-clicking on each parameter, you move them between the two alternative categories.
If you want to model the thickness of a layer, we recommend that you have the density of that layer fixed in the model, since the two parameters are connected to each other (high density/small thickness is equal to low density/large thickness, for a certain amount of mass) and the software will have a problem to find one single solution.
Normally, the parameters ‘thickness’, ‘viscosity’ and ‘shear modulus’ are chosen as parameters to fit. The density is then assumed to be the same during the whole measurement. The input values for the parameters to fit are set as an interval, with ‘maximum guess’ and ‘minimum guess’ values inserted in the table.
The values for the fixed parameters need to be rather accurate—the easiest way to find out how exact they need to be, is to play around with the values and observe the fluctuations of the model output.
When do I use the extended modeling with overtone dependence?
The extended model has been introduced since there was a demand from many customers to be able to test the frequency dependence of the viscoelastic parameters. In the extended model, a possible frequency dependence on viscosity and elastic shear modulus has been introduced. Normally the viscoelastic behaviour follows linearly the shear frequency on a log-log scale, which means that it obeys a power-law function. This and, which is applicable to some cases, a pure linear dependence have been implemented in the software.
How do I work with L1 and L2 modeling?
Checking ‘L1’ when modeling a two-layer system (or any multilayer), means that QTools will treat the film as one homogeneous film, finding an average value for each parameter (viscosity, shear modulus and density) for the whole film. The modeled thickness will be the total thickness for the whole film.
Checking both ‘L1’ and ‘L2’ means that QTools will try to find a solution with two regions having different properties, with ‘L1’ being the innermost layer. The more distinct the interface is (i.e. the larger the difference is between the two layers), the better the chance of finding a good fit.
A good way to investigate a two-layer system is to build it sequentially during an on-going measurement, so that you can model the first layer (first part of the measurement) separately, using only ‘L1’. When this is done, set all modeled ‘L1’ parameters as ‘fixed parameters’, then include ‘L2’ and model the properties of the second layer. This approach assumes that the properties of the first layer do not change when introducing the second one.
If I choose to model a system with two layers, would I get the same mass and thickness of L1 and L2 as when I choose a one-layer model?
The thickness of a L1 modeling would be the same as the total thickness of a L1+L2 modeling, if the viscoelastic properties of the two layers are close to each other. In case of e.g. a rigid layer and a soft layer and different densities, the L1 modeling will find viscoelastic output parameters that are an average between the two layers. In such case the total thickness might be slightly different from the one obtained using a two-layer model.
My system includes more than two layers—can I still model them one by one?
You cannot model them all at one time. The approach to model each layer separately would be to group the ‘L1’ and ‘L2’ as one layer—forming a new ‘L1’ layer—and treat layer 3 as the new ‘L2’, while disregarding the averaged viscoelastic results for the ‘L1’ layer (same idea as described above, under ‘How do I work with L1 and L2 modeling?’). The approach requires that the build-up of the multilayer is done sequentially within one measurement data set.
Can I apply the modeling to a film made outside the QCM-D instrument?
Yes, you can: measure the non-coated sensor first, so that you get a QCM-D baseline before the treatment of the sensor; then, after the external treatment you measure the processes on the treated sensor, as usual. Remember to use the same medium above the sensor in both measurements to be able to compare data. With QSoft 401, you then merge the two files by using the ‘Stitch files’ function and model the data in QTools the standard way. With QSoft 301 it is a bit more work: you need to un-offset the data in the first measurement file, which means when you open the QSoft file, you do not accept the ‘File transcriber’ suggestions to offsets and scaling; then copy the baseline from the first measurement and insert it in the beginning of the second, non-offsetted, measurement file, to get the right baseline reference in QTools.
How do I perform degradation experiments? What is there to consider compared to adsorption experiments?
Generally, experiments are made on a bare sensor and then something is adsorbed to it during the measurement. In these cases you can say that if D is larger than zero and if the overtones are spreading, the film is soft and requires viscoelastic modeling.
In some cases, a film is coated on the sensor before the measurement and then something is adsorbed onto that during the measurement. If the initial film is rigid and is not affected (for example degraded or swollen) during the measurement, the statement above is also valid.
This is not true, however, if you coat the sensor with a film that is not rigid and/or is affected during the measurement (degradation, swelling etc). Wevcannot judge if the film is soft or not from just looking at Δf and ΔD because f and D are not shown as absolute values but only in relation to the base line (therefore called Δf and ΔD). Since the baseline represents the sensor (which is coated) at the beginning of the measurement and is not related to the bare sensor, we will not be able to draw conclusions on the changes relative to the bare surface.
However, if we can add the baseline of the bare sensor before coating, to the beginning of the degradation measurement then this would be a solid ground to stand on and in relation to this we can judge if the film is soft or not based on the above statement.
So how do I do this?
Measure the sensor in the instrument with the same buffer as you will use in your experiment. Then coat the sensor and do your measurement. The first measurement could thereafter be stitched to the beginning of the second measurement, so that they are in the same file. Now the measurement will show the bare sensor in fluid, thereafter there will be a jump in f and maybe in D to the coated sensor in fluid and thereafter the degradation.
Note that this is not a standard procedure! There might be some stress in the sensor from mounting so the absolute f and D can differ from time to time. You should try mounting the sensor several times to see if the difference in absolute f and D varies a lot by looking at the absolute values of f and D in the data sheet in QTools. Hopefully it doesn’t differ too much and then you can use this procedure to get the baseline in order to model.
Is there a way to estimate the quantity of an adsorbed protein, or similar, with water excluded, even though it is probed in hydrated form?
The QCM-D will give the hydrated mass, i.e. the mass of the molecules adsorbed to the surface and the solvent that is trapped in between. There is no means to extract the mass of only the molecules with the QCM-D technique. However, the dissipation may give a hint on the hydration of the formed layer. For example, if you have a really, really high dissipation with spreading of overtones you may conclude that the molecules have arranged themselves in an extended and sparse fashion which allows plenty of solvent to be trapped. If the dissipation is low and the spreading of overtones is not so significant, the molecules have probably arranged themselves in a more dense and ordered fashion not allowing so much solvent to be trapped. In this case the QCM-D mass will be a closer estimate to the mass of the molecules than the QCM-D mass for the soft layer.
If I increase/decrease the density, the thickness values also change. So, how to guess the best value for the density?
Yes, your thickness will vary depending on L1 density value, since they are correlated. You need to state in your experimental section ‘an estimated L1 density of YYY kg/m3 was used’. You can change the L1 density, the fit should be equally good, but your thickness will change. If you know that your film is 50% hydrated, you can calculate the L1 density:
0.5 · ρdry layer + 0.5 · ρbulk solution
However, this is something that is almost impossible to know. For hydrated biomaterials the density is close to, however slightly larger than, that for water.
Would the viscosity and shear modulus be zero or infinite for a rigid material?
If it is a solid, the elasticity is very high, and the viscosity is very low. Think of the energy losses when sound is transmitted through a material: a good material for sound transfer has low viscosity, and so has quartz almost no viscosity but high elasticity. Maple syrup has high viscosity, which means it is not a good material for sound transfer—it dissipates a lot of energy.
I have difficulties finding a good fit to my data.
There may be several reasons why it is difficult to find a good fit:
- The D-factor is very low (<1), especially in comparison to the frequency shifts. The modeling requires that there is viscoelastic behaviour of the adsorbed film. If there is not, the modeling is not applicable and the Sauerbrey function is enough to extract mass and thickness data. Viscoelastic data is not possible to extract, simply because the film is too rigid.
- You are trying to model both density and thickness at the same time. When modeling a viscoelastic film, it is generally not possible to separate between these two parameters in much the same way as it is not possible to separate density and viscosity for a Newtonian fluid. You will usually get an equally good fit if you at the same time increase the density by 10% and lower the thickness by 10% (so that the product stays the same).
- The adsorbed films do not fulfill the assumptions made in QTools. A good fit requires that the adsorbed films have a homogeneous density, viscosity and/or shear modulus. If you, for instance, have fitted your data using a fixed density, it could be worth considering if this parameter is changing during different parts of the measurement.
- Your minimum and maximum guesses for the initial search grid are not optimal. Changing the extreme values will give a new set of coordinates, even within the grid, and new solutions to the fitting may be found.
- The data set does not include all coating/measurement steps. QTools assumes that the beginning of the measurement reflects the non-coated rigid sensor surface material. If you, for instance, coat the crystal ex situ with a film and then insert it in the chamber for measurements, you need to have taken a short baseline on the non-coated surface before the coating step as reference, and then combine the two data sets before using QTools.
- The fundamental tone is included in the fitting. We do not recommend using the fundamental frequency (5 MHz) when doing liquid measurements since this resonance is much more susceptible to mounting mediated stresses that are aggravated by liquid loading. If the first harmonic is unchecked in the modeling, you will get a better fit.
I get much larger noise in QTools, than in QSoft, for the same data.
If you zoom in your QSoft data, they will appear the same way. It is the averaging function in QSoft that does this: if every single data point would be plotted in QSoft, the software would be too slow, i.e. too much processor time would be spent on updating the plots, which would slow down the acquisition speed drastically. So, instead of plotting all points, only one average of them is plotted for each x-pixel.
My QTools spreadsheets are blacked out.
Some of the Windows settings for data table cell color do not show cell contents properly in QTools. The settings should be accessible under ‘Control Panel’ › ‘Display’ › ‘Appearance’. Select any of the other ‘Color Schemes’ and you should be able to see the data in the cells.
I can’t get a reliable modeled viscosity ‘baseline’.
A reason for unexpected values of modeled viscosity or other parameters when there is nothing adsorbed onto the sensor surface, could be that the measured f and D values are very close to zero. If so, the model may have a problem finding good solutions when fitting. This typically happens in the beginning of an adsorption process, or more precisely, right before anything has been adsorbed. Because of this, the default modeling settings start the fit at the end of the measurement and proceed backwards (this is indicated by the quick-button illustrated by an arrow in the Modeling Centre).
I have experienced that thick coatings and/or non-even coatings sometimes results in high overtones being noisy. Are higher overtones less sensitive because they are dampened too much?
The electrical signal strength (voltage) that reaches the instrument decreases as the overtone number goes up. Dampening will decrease the signal strength and when it is low enough, QSoft will lose the overtone.
What is a good ChiSqr?
You cannot really predict Chi-square, since it will be different for different data sets. It is not divided by the number of data points in the data set, which means that if a data set is twice the size as another data set, it will also give twice as large Chi-square for an equally good fit.
Biolin Scientific systems are precision instruments, providing accurate and reliable results. To ensure that you and your instrument maintain peak performance, we offer a number of service and support solutions. See more information below.
The Q-Sense Service Contracts ensure the very best utilization of your instrument as we stay by your side throughout the use of your equipment. Including preventative maintenance, support and possible repairs and training, our team of certified service engineers and experienced application specialists will make sure that your instrument is always running at its best.
|Technical support by phone and email||Included||Included||Included|
|Preventative maintenance once/year||Included||Included||Included|
|Onsite training and support once/year||*||*||Included|
Preventative maintenance ensures that your instrument stays in shape and produces accurate and reliable results. It includes:
• Exchange of typical wearable parts
• Software updates
• Functionality verification test
• Certificate of performance
Contact us to discuss your service and support needs!
*Available upon request and invoiced separately. 1Onsite for Q-Sense Pro and Q-Sense E4 Auto. 2Onsite for all
systems. 3Considers parts and labor. The service contracts are available for Q-Sense Explorer, Q-Sense Analyzer, Q-Sense Pro and Q-Sense E4 Auto.
Training will help you get the most out of your Q-Sense instrument. Our educational range aims to get you comfortable in the laboratory so that you can discover the many ways QCM-D can bring your research forward. By offering assistance and education on data analysis and data modelling we also help you to make the most of your experiments and your time invested in the laboratory.
Click here for an overview of our training programs in PDF format.
Start-up Training with instrument purchase
In order to guarantee optimal performance from the very beginning, we offer start-up training. Start-up training covers hands-on operation of the instrument as well as data evaluation. The training enables users to exploit the full potential of the QCM-D system. Start-up training is practically handled differently around the globe, either at customer site, at our training center or other agreed set-up. Ask your local sales representative or email firstname.lastname@example.org for more details.
QCM-D Refreshers Course
Sign up for our QCM-D refresher course running at our office in Gothenburg September 20-21, 2016.
Running a Q-Sense instrument and setting-up a QCM-D experiment is easy if you know how to!
Get hands-on instrument experience and learn more about applications and the many possibilities of your Q-Sense instrument. Our Application Scientist will walk you through experimental set-up, instrument operations and increase your knowledge on the theory and technology of your Q-Sense instrument. Also let us inspire you with application examples from a number of different research fields and application areas.
The course focuses on hands-on training and application inspiration, we want you to realize the many possibilities of QCM-D.
For our courses we welcome you to one of our training and innovation centers located in Göteborg (Sweden), New Jersey (USA) and Shanghai (China).
• Understanding of QCM-D theory and technology.
• Experimental design and set-up.
• Learn how to operate and set-up own Q-Sense instrument and modules in an optimal way (Q-Sense Omega and/or Q-Sense E-series instruments and specialized modules).
• Understanding and interpretation of data output.
When: Scheduled courses are run regularly at all training and innovation centers, please check our calendar for specific dates.
Where: Courses are held in our training and innovation center in Göteborg (Sweden), New Jersey (USA) and Shanghai (China). Please inquire for other locations.
Maximum number of participants: Pending on site, enquire for further info.
Contact and further information: Please email email@example.com or contact your local sales representative for more details on course agendas and practicalities.
Custom-made training courses to meet your needs
Are you a number of people in your department, research group or institute that would benefit from a QCM-D course?
Or, have you been running experiments for a while, but want one-on-one education and guidance by our Application Scientists to get the most out of your own data?
Let us help you! We offer custom made courses where the curriculum is individualized from your/your group’s needs. Using the agenda for the QCM-D Refreshers Course, together we discuss your needs, decide goals and set the tailored course agenda.
We run custom made courses in our training centers, or we travel to your site. Contact us for further information, firstname.lastname@example.org.
Q-Sense Scientific User Meetings
The QCM-D scientific meetings are excellent opportunities to learn from and share thoughts with other QCM-D users and to get support on data analysis on an individual level. The meetings have been well attended and much appreciated over the last few years. Check out our calendar for the next Scientific User Meeting, or email email@example.com.
We offer live webinars about applications, QCM-D data analysis and products. The application webinars have specific topics and are sometimes held by external scientific researchers. If you join a live webinar you have the chance to ask questions directly and discuss with the presenter. Check out events to see what upcoming webinars we have. We also record many of our webinars. Check them out below.
Below is a selection of what you can find among our recorded webinars.
- QCM-D for Drug Discovery and Protein Formulation Analysis
- QCM-D for Drug Storage and Formulation
- QCM-D as a Tool to Study Infectious Diseases
- EQCM-D to Investigate Conformation Changes in Redox Enzymes and Effect on Catalysis
- QCM-D for Cell Adhesion Studies in Cancer Research
- QCM-D and Cells – The Importance of the Interfacial Layer Between the Cells
- QCM-D for Bacterial Adhesion Studies
- Q-Sense Bio-sensors (Biotin, His-tag Capturing, Amine Coupling) for Functional Protein Immobilization
- Reconstitution of nanomachine in biological membranes
- QCM-D for Analyzing Nanoparticle Interactions in the Environment
- QCM-D for Water Cleaning Applications
- Characterizing and preventing the threat of corrosion QCM-D
- QCM-D Applications in Development of Marine Anti-biofouling Materials
- Nanoparticle Analysis with the QCM-D Technology
- Q-Sense Solution-Printing of High Performance Organic Semiconductors
- Monitoring Phase Transitions in Liquid Crystals and Lipids Using QCM-D
Oil and Gas
- QCM-D for Crude Oil and Asphaltene Adsorption Studies
We offer live webinars about applications, QCM-D data analysis and products. The application webinars have specific topics and are sometimes held by external scientific researchers. If you join a live webinar you have the chance to ask questions directly and discuss with the presenter. Check out events to see what upcoming webinars we have. We also record many of our webinars. Check them out below.
See recorded QCM-D Data Analysis Webinars
- QCM-D Analysis Methods
Introduction to qualitative and quantitative analysis of QCM-D data including Sauerbrey and viscoelastic modeling.
- Viscoelastic Model — Theory
Theory about viscoelasticity and how the model is applied in QTools.
- Viscoelastic Modeling in QTools
Guide through the modeling center for viscoelastic modeling of soft films.
- Viscoelastic Modeling of Two Layers in QTools
Three different approaches of analyzing two layer films with the viscoelastic model.
- Frequency Dependent Viscoelasticity — Theory
Basic theory about frequency dependent viscoelasticity.
- Extended Viscoelastic Model in QTools
Guide to the extended viscoelastic model in QTools, which takes into account frequency dependent viscoelasticity.
- Q-Sense Product Family Flyer
- Q-Sense Pro
- Q-Sense Analyzer
- Q-Sense Explorer
- Q-Sense Modules
- Q-Sense Dfind Software
- Service and Support Overview
1. Enzymatic Degradation of Lipid Films Caused by Lipase
2. Structural Change of Adsorbed Protein Layer
3. Analyzing Surface Induced Complement Activation
5 .Early Detection of Biofilm Formation on Steel Surface
9. The QCM-D Technology To Study Surfactant/Surface Interactions
10. Studying Nucleation Kinetics of Bioceramics
14. Protein Fibrillation Studied with QCM-D
15. Molecular Conformational Effects on Protein-DNA Interactions
16. Protein Viscosity Analysis Using QCM-D
18. Analyzing Humidity Effects Using QCM-D
19. Analyzing Cleaning Processes Using QCM-D
20. Ellipsometry and QCM-D on the Same Surface
21. Ab-Ag Interaction Studies on Q-Sense Biotin Sensor
22. QCM-D as Screening Tool for Protein Adsorption on Container Systems
23. Polyelectrolyte Multilayer and Crosslinking
24. QCM-D for Nanotoxicology Assessments
25. Asphaltenes and Crude Oil Adsorption
26. Enzymatic Hydrolysis of Cellulose
27. Analyzing Fuel Cell Corrosion by Electrochemical QCM-D
28. QCM-D to Study Dissolution Mechanisms in Photoresist Polymers
29. Improved Understanding of Lipid Membranes Through Combined QCM-D and EIS Measurements
30. QCM-D in Drug Formulation and Storage
31. Improving Dye-Sensitized Solar Cells With the QCM-D Technology
32. Using the QCM-D Technology to Characterize Membrane Water Permeability
33. QCM-D in Combination with light Microscopy to Follow Changes in Live Cell Morphology
34. Characterization of Polymer Layer Swelling and Collapse by the QCM-D Technology
- Biomaterials Research
- Detergent Effectiveness
- QCM-D for Drug Discovery
- QCM-D for Studies of Bacteria
- QCM-D for Studies of Nanoparticles
- QCM-D for Studies of Polymers
- Quartz Crystal Microbalance with Dissipation (QCM-D)
- Electrochemistry QCM-D
- Ellipsometry QCM-D
- Lipid Bilayer Formation Using the Q-Sense Open Module
The animation includes an introduction, an overview of the instrument followed by a number of application examples. Thereafter a closer look at the instrument and how it is operated.
Including introduction, measurement principle and output data possible to obtain with QCM-D. The animation also shows three application areas and shows the set-up and how the instrument is operated.
Animation showing QCM-D measurements of different types of applications. Contains all individual measurement examples.
Individual Measurement Examples
|Adsorption of two different proteins to the surface. How QCM-D measures changes in mass and structure (rigidity of the different layers) of the layers as they adsorb to the surface.||Download & View|
|Cell adhesion to two different surfaces measured with QCM-D and with microscopy. How microscopy alone cannot detect the difference in surface attachment that is detected with QCM-D.||Download & View|
|Cross-linking of a molecular layer induced by an environmental factor (e.g. pH or salt change in the fluid flushed over the sensor). How the thickness and structure of the layer is measured when the molecules cross-link and collapse on the sensor.||Download & View|
|Degradation of a lipid film/stain by for example a detergent, enzyme, or single surfactant. How QCM-D can be used to measure desorption rates, swelling, and degradation of films on the sensor.||Download & View|
|Multilayer build-up The thickness and structural changes of each layer are measured as the polyelectrolyte multilayer is growing.||Download & View|
|Swelling measuring rigidity, thickness, and water content of a polymer film as it swells due to changes in the surrounding medium.||Download & View|
Please go to the User Area below to log in and download user information such as instrument manuals, cleaning protocols and software updates.
If you are a Biolin Scientific Q-Sense customer you may create a user account to access the User Area. In order to get an account, the serial number of your Q-Sense instrument is required. The serial number is found on the back of the electronics unit.
If you need any help, please contact firstname.lastname@example.org.
The User Area is password protected and only available for Biolin Scientific Q-Sense customers. If you had a login account on the previous Q-Sense website, type in your email address associated with that account in the missing password section below, and you will get a new password automatically. You find the login section if you click on the arrow below.