Sub-picomolar dopamine sensing in aqueous electrolyte with surface-engineered MXene-gated organic transistors

Electrolyte-gated organic transistors (EGOTs) can be operated as sensors with high selectivity and an outstandingly low limit of detection. Their response to interfacial interactions occurs either by capacitive coupling between gate and channel or by faradaic reactions. In this work, we endow a high-affinity sensing response to EGOTs based on the PEDOT:PSS channel by functionalization of the gate electrode with Ti3C2TX MXenes. MXene were synthesized in different conditions to tailor surface chemistry, while retaining a similar skeleton structure. The integration of MXene-based functionalization layers is shown to preserve the high transconductance in EGOT devices, while simultaneously tuning the switch-on voltage toward 0 V. This modulation enables a safe operational window in aqueous electrolytes, preventing unwanted electrochemical side reactions. We then demonstrated that EGOT with the surface-tailored MXene layers are sensitive to concentrations of the neurotransmitter dopamine down to sub-picomolar levels of detection. These unprecedented LODs indicate that modification of EGOTs gate with tailored or functionalized MXenes is a viable and versatile strategy to enhance sensitivity to relevant biomarkers.