With the development of microsensors and microactuators, recent research efforts have been made towards utilizing these miniature instruments in biological applications. Flexural plate-wave (FPW) sensors are an example of such a micro-device. They belong to a family of sensors often termed acoustic sensors and are quite similar in operation to surface acoustic wave (SAW) sensors. The theory and development of FPW sensors have been discussed in previous work and a variety of applications have been found for this very versatile sensor. This work explores a particular aspect of the sensor's many capabilities, namely, biosensing applications of the sensor coated with a gel. In particular, we will demonstrate how FPW sensors can be used for measuring diffusion coefficients in gels and other filtering layers, and explore methods of using the FPW sensor as a microbial sensor.
We will first discuss initial work that was performed after the discovery that FPW sensors operate in gels. These experiments gave preliminary results using the FPW sensor to monitor the metabolism of yeast immobilized in an alginate gel. Results indicate that the FPW sensor can be used to infer the metabolic rate of yeast cells based on measurements of ethanol production. We then describe experiments in which we use a gel-coated sensor in a flow cell to measure diffusion coefficients of solutes in polyacrylamide and agar-based gels. These experiments demonstrate that FPW sensors can be used to make accurate measurements of diffusion coefficients in gels. We will also explore several potential FPW applications and suggest improvements to the experimental apparatus, as well as discuss the current limitations of our work.