Direct Electrochemical Signaling in Organic Electrochemical Transistors Comprising High-Conductivity Double-Network Hydrogels

In composite hydrogels, the high electrical performance of poly(3,4-ethylenedioxythiophene) complexed with poly(styrenesulfonate) (PEDOT:PSS) is integrated with complementary structural and electrochemical functions via a rationally designed poly(acrylamide) second network incorporating phenylboronicacid (PBA). Free-standing double-network hydrogels prepared by a simple one-pot radical polymerization exhibit stateof-the-art electrical conductivity (similar to 20 S cm(-1) in phosphate buffered saline) while retaining a degree of hydration similar to that ofbiological soft tissues. Low resistance contacts to Au electrodes are formed via facile thermo-mechanical annealing and demonstrate stability over a month of continuous immersion, thus enabling hydrogels to serve as channels of organic electrochemical transistors (OECTs). Despite thicknesses of similar to 100 mu m, gating of hydrogel OECTs is efficient with transconductances g(m) similar to 40 mS and on/offratios of 10(3) in saturation mode operation, whereas sufficiently high conductivity enables linear mode operation (g(m) similar to 1 mS at -10 mV drain bias). This drives a shift of sensing strategy toward detection of electrochemical signals originating within the bulky channel. A kinetic basis for glucose detection via diol esterification on PBA is identified as the coupling of PBA equilibrium toelectrocatalyzed O-2 reduction occurring on PEDOT in cathodic potentials. Hydrogel OECTs inherently amplify this direct electrochemical signal, demonstrating the viability of a new class of soft, structural biosensors.

Automated summary

This study successfully integrated the high electrical performance of poly(3,4-ethylenedioxythiophene) complexed with poly(styrenesulfonate) and the structural and electrochemical functions of a poly(acrylamide) second network incorporating phenylboronicacid in composite hydrogels. The free-standing hydrogels showed excellent performance in terms of hydration and conductivity, and could be used as channels for organic electrochemical transistors.