Sometimes the collected data is merely used for our information and convenience, such as giving us a clue as to whether to bring an extra sweater when we go out. But it can also be used as input for regulation and control, for example, to verify that a pressure value stays within predefined maximum and minimum values. Each sensor type is based on a specific detection method that enables the monitoring of the parameter of interest.
A subgroup of sensors is biosensors. Biosensors exploit biological recognition systems designed by nature to detect an event, such as an analyte binding to a receptor. This information is then converted and collected as a readout. Sensors based on conducting polymers are under intensive investigation due to their high application potential. Langmuir- Blodgett technology has been utilized in sensor applications as it is able to produce highly organized thin films with controlled thickness. These sensors have been utilized in gas sensing applications as well as for the detection of trace amounts of antibiotics in solutions. Different means for detection vary from luminescence to conductivity measurements.
Biosensors are used in many areas, such as in medical applications, in the food industry, and in defense. In addition to the biological recognition element, a biosensor consists of two more elements; a transducer which can detect the biorecognition event, and an interpretable readout signal. The transducer can be based on different principles. A common transducer principle is acoustic, such as the quartz crystal microbalance (QCM). The QCM, where detection is based on the piezoelectric principle, is an established method in biosensing, and has been used for decades in biosensor development and applications.
The biological detection system of the biosensor can be intricately designed in layers and various configurations, based on building blocks such as antibodies, proteins, DNA, cells, lipid-based structures, carbohydrates and nanoparticles, as thoroughly outlined in this extensive and detailed acoustic biosensor review. The building blocks and recognition components range from small to large, and enables the detection of everything from heavy metal ions and DNA hybridization to cell attachment, proliferation and growth, as well as cell response to external stimuli. The range of potential detection systems is vast, and sensor interfacial strategies for improved sensitivity and selectivity are continuously being explored.
As miniaturized devices are gaining more attention, newly developed nanomaterials can take this development even further. Many of these materials are not available for use in conventional microfabrication methods, so emerging techniques are being utilized.
Conducting polymers such as polyaniline, polythiophene, polypyrrole and their derivatives have been used as active layers for gas sensors as well as for enzyme immobilization to make biosensors. Sensors made of conducting polymers have many improved characteristics such as high sensitivity and short response time. Conducting polymers are also easy to synthesize and they have good mechanical properties. LB can be used to fabricate highly controlled thin films of conductive polymers on relatively large areas.