Fabrication of a Solution-gated Indium-Tin-Oxide-based One-piece Transistor Enabling Sensitive Biosensing

A simple and rapid method to fabricate a solution-gated one-piece indium-tin-oxide (ITO)-based ion-sensitive field-effect transistor (ISFET) (ITO-ISFET) for biosensing is presented in this report. Although ITO is a conductive oxide, it exhibits semiconducting properties at a depletion layer thickness of approximately 20 nm or less, making it suitable as the channel of a pH-sensitive solution-gated ISFET. Specifically, by etching the middle part of a conductive ITO single thin film with an acidic solution to make it ultrathin, a one-piece ITO-ISFET with a semiconductive channel can be fabricated. The source, drain electrodes, and channel are fully integrated without any interfaces. The ITO channel surface is then soaked in sample solutions with a reference electrode, enabling it to function as a solution-gated ISFET. Thus, the one-piece ITO-ISFET can be fabricated simply and rapidly using only sputtering followed by etching through a photolithography technique, with the sample solution conveniently serving as the gate.