The maximum mass sensitivity in liquid is about 0.5 ng/cm2 for QSense Pro and Analyzer/Explorer if measuring at a rate of one data point every five seconds. QSense 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).
The frequency range is 1-70 MHz with QSense Pro and Analyzer/Explorer. A large range is important to be able to use the unique features of multiple frequency and dissipation sampling.
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 QSense 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.
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.
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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.
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.
The maximum rate is up to 200 data points per second, giving you a high-resolution real-time measurement suitable for fast reactions.
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 QSense 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.
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.
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.
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.