J. Koerner, C.F. Reiche, H-Y Leu, J. Magda, F. Solzbacher
University of Utah,
Keywords: hydrogel, polyimide, bending sensor, biomedical application
Summary:Smart hydrogels are highly biocompatible polymeric materials which change their volume in the presence of an analyte they have been tailored for by molecular imprinting or aptamer-based approaches. These properties make hydrogels ideal candidates for the development of biomedical sensors. The challenge in sensor creation lies in the reliable, fast and sensitive detection of the hydrogel’s volume change. Many different approaches have been employed, e.g. miniaturized silicon pressure sensor chips, cantilever sensors and fluorescence-based methods, all with their own advantages (high sensitivity for a specific analyte in case of fluorescence) and disadvantages (biocompatibility issues for silicon pressure sensors; fluorescence only works for certain analytes). To overcome these restrictions, we have developed a universal sensor platform based on a thin polyimide strip (~20 µm thickness) with embedded meandering metallic leads. The smart hydrogel, tailored for a specific analyte, is attached to one side of the polyimide. Any volume change of the hydrogel influences the bending of the sensor, resulting in an electrically detectable impedance change of the embedded lead structure. Through calibration measurements, the impedance change can be related to a corresponding change in analyte concentration. Furthermore, the sensing structure can be equipped with different types of hydrogels and it can be tailored for the target application in terms of dimensions, therefore having the advantage of being a universally applicable sensor platform. In first proof-of-principle experiments, sensors of different dimensions have been fabricated, equipped with acrylamide-based hydrogels and tested with varying salt concentrations (ionic strength response of the hydrogel). Results indicate a very fast and strong response. With the basic sensor principle demonstrated, next steps include the optimization of the embedded metallic lead structure to increase signal strength and SNR as well as testing of different hydrogels tailored for various biomedical analytes. Our target applications at this point lie in the real-time monitoring of biomarker and medication levels which are critical during surgeries and stationary patient care. Our suggested polyimide-based sensor platform would be an ideal candidate for incorporation into catheters used for drug administration without requiring a change in clinical routine or increasing the patient’s discomfort. In summary, the advantages of the proposed concept are: universality (sensor can be equipped with different hydrogels whichever analyte is targeted), short reaction-time (bending occurs immediately when the hydrogel surface is exposed to the analyte), biocompatibility and ease of incorporation in clinical procedures (catheter sensor). Florian Solzbacher declares financial interest in Blackrock Microsystems LLC and Sentiomed, Inc.