PEDOT:PSS Hydrogel Based Wearable Biosensor Utilizing Aerosol Jet Printed Organic Electrochemical Transistors (OECTs) for Lactate Detection

Poly (3,4-ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS) is a conductive polymer with excellent electrical conductivity, good processibility and biocompatibility. Hydrogels have the advantage of soft, flexible and non-toxicity with cells and tissues. A combination of PEDOT: PSS and a hydrogel offers unique conductivity and mechanical properties, applying an alternative approach for biosensing applications.<br/><br/>In this work, we developed a PEDOT:PSS hydrogel based 3D printed organic electrochemical transistor (OECT) for lactate sensing, since OECTs offer high transconductance, low operation voltage and compatibility with aqueous environments. Optomec Aerosol Jet 5X 3D printer is used to fabricate the biosensors on the flexible Kapton substrate. Au was chosen as the metal contact, Pt as the gate with polyimide as the insulator layer. PEDOT:PSS hydrogel is drop casted on Au as the channel material. For PEDOT:PSS hydrogel, it was synthesized by mixing with dimethyl sulfoxide (DSMO) to improve the conductivity under vigorous magnetic stirring for 24 hours, then drop-casted 0.2uL solution on top of the channel for a printed OECT device and was placed into the oven under 60°C for another 24 hours to generate the partially formed gel. After that, 3 times cyclic annealing was applied for the device for 30 minutes at 130°C. Finally, the device was put under -20°C for 12 hours and took out for extra 12 hours, repeating 2 times. The unfunctionalized device exhibits a transconductance up to 110 mS and is compared to the printed PEDOT:PSS based device. Further, tetrathiafulvalene (TTF), chitosan, lactate oxidase (LoX), bovine serum albumin (BSA) and gelatin help realize the functionalization of the device. The functionalized lactate sensor can be preserved in PBS solution under 4°C for over one month. Spike tests on the PEDOT hydrogel-based lactate sensor was performed and achieved a sensitivity range between 100uM and 10mM. In addition, the combination of the printed PEDOT:PSS channel with drop-casted PEDOT:PSS hydrogel exhibited better performance of the device. The results for this device will be presented along with the material characterization.