Influence of geometry on dopamine sensing by organic electrochemical transistors

Organic Electrochemical Transistors (OECT) have emerged as a promising biosensing platform due to their unique combination of high signal amplification, water compatibility, biocompatibility, and their ability to transduce ionic signals to electronic signals. A myriad of different sensors have been reported over the past two decades, from monitoring simple salt concentrations, biomolecules or bacteria, to the integrity of cellular barriers. Previous models of OECT sensing have indicated that the sensitivity of these devices can be increased by reducing the area of the gate in relation to the channel. Here, we investigate if a similar trend occurs for OECT-based dopamine sensors by analyzing the impact of varying channel-gate area ratios ( γ ) on their performance. Through steady-state and transient characterization, the sensing capabilities and stability of OECTs with six different γ (0.01, 0.1, 1, 10, 100 and 1000) are evaluated. We show that, in contrast to previous reports, the sensitivity is not monotonically increasing with decreasing gate area, but peaks at an optimal channel-gate area ratio of approximately ten. We explain this trend by a balance between two trends—increased voltage drop at the gate for smaller gates, and increased transconductance for larger gates. Overall, these findings suggest that a careful optimization of γ is needed to obtain a balance between signal amplification and sensitivity.