Miniaturization of Aptasensors in Organic Electrochemical Transistors for Sensitivity Enhancement.

Aptasensors have received intense interest because of their selectivity and synthetic flexibility. Aptamer bioreceptors were recently combined with organic electrochemical transistors (OECTs) to increase the signal strength. Although promising, a lack of fundamental understanding of the scaling of these OECT-based aptasensors makes targeted optimization of these devices challenging. Here, we study the influence of the gate electrode area on sensitivity, detection range, and selectivity systematically. To increase the ratio between gate and channel area further, we, for the first time, combine the aptasensor with a vertical OECT (VOECT), yielding a sensitivity as high as 0.3 mA/dec. Furthermore, the response of the OECT aptasensor is already significant at gate voltages close to 0 V, thus avoiding undesired electrochemical processes such as gold oxidation or radical oxygen formation. Overall, the combination of OECT and aptasensor serves as an important step toward a miniaturized biosensor with amplified sensitivity and continuous sensing capability. The present study not only extends our understanding of gate scaling on the sensor response but also provides design rules to reach very high sensitivity at low operational voltages.