Fully 3D printed OECT based logic gate for detection of cation type and concentration

Flexible biosensors have an ever-growing market which requires economical, reliable and fast sensors. Ions play an important role in the proper functioning of humans, animals and plants. Thus, it is important to be able to measure the ion concentration accurately. Here, we demonstrate a fully 3D printed inverter logic gate sensor based on organic electrochemical transistors (OECTs) with Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as the channel material to operate as an ion level detector. Based on tests with various electrolytes like NaCl, KCl and CaCl2, we demonstrate that the inverter logic gate can be used repeatably and reliably as a cation type and concentration sensor. For these thicker channel devices, nearly 9 mu m, we demonstrate a limit of detection (LOD) of 1mM for NaCl, CaCl2 and KCl electrolytes. These sensors demonstrate a very high sensitivity of 650 mV/dec and 200 mV/dec (both greater than the Nernst limit of 59.2 mV/dec) in the range of the 1-100mM and 100-1000mM electrolyte concentration for Na+ ions. In addition, the switching voltage shift of these sensors can be used directly to infer the type of cation being detected. Thus, these sensors can be used as individual ion sensors or in a circuit for multiplexing applications with other printed electronics for biosensing or bio wearables.