Sensing small neurotransmitter–enzyme interaction with nanoporous gated ion-sensitive field effect transistors

► Nanoporous gate ion-sensitive field effect transistors for sensing neurotransmitter–enzyme interactions. ► High surface area nanoporous gates with pores diameter 20–35nm are produced by anodizing process. ► Gate-source voltages of the transistors demonstrate a pH-dependence. ► Physical immobilization of tyrosinase on the gate. ► Fast response time for highly sensitive and selective detection of dopamine at micromolar range. Ion-sensitive field effect transistors with gates having a high density of nanopores were fabricated and employed to sense the neurotransmitter dopamine with high selectivity and detectability at micromolar range. The nanoporous structure of the gates was produced by applying a relatively simple anodizing process, which yielded a porous alumina layer with pores exhibiting a mean diameter ranging from 20 to 35nm. Gate-source voltages of the transistors demonstrated a pH-dependence that was linear over a wide range and could be understood as changes in surface charges during protonation and deprotonation. The large surface area provided by the pores allowed the physical immobilization of tyrosinase, which is an enzyme that oxidizes dopamine, on the gates of the transistors, and thus, changes the acid–base behavior on their surfaces. Concentration-dependent dopamine interacting with immobilized tyrosinase showed a linear dependence into a physiological range of interest for dopamine concentration in the changes of gate-source voltages. In comparison with previous approaches, a response time relatively fast for detecting dopamine was obtained. Additionally, selectivity assays for other neurotransmitters that are abundantly found in the brain were examined. These results demonstrate that the nanoporous structure of ion-sensitive field effect transistors can easily be used to immobilize specific enzyme that can readily and selectively detect small neurotransmitter molecule based on its acid–base interaction with the receptor. Therefore, it could serve as a technology platform for molecular studies of neurotransmitter–enzyme binding and drugs screening.