IGZO-based electrolyte-gated field-effect transistor for in situ biological sensing platform

An amorphous indium gallium zinc oxide (IGZO)-based electrolyte-gated field-effect transistor (IGZO-EGFET) was fabricated and its feasibility as a biological sensing platform was evaluated. Herein, a 50-nm-thick IGZO thin film deposited via radio-frequency sputtering was utilized as both the active channel and biological interface of the device. The fabricated IGZO-EGFET operated by inducing a gate voltage directly through the liquid electrolyte at a low bias range (∼±1.5 V) with a subthreshold swing of 185 mV dec−1. The high uniformity of electrical characteristics for the devices were confirmed with 11.4% chip-to-chip deviation by measuring the threshold voltages (Vth), and the shift of Vth was employed as a major parameter to determine the biological interactions. In order to assess IGZO-EGFETs as a biosensing platform, first, pH sensing was conducted with and without amino-silanization on the IGZO surface. The amine-modified device showed steeper slope between Vth shifts and pH variations (68.5 mV pH−1) than that (32.7 mV pH−1) of the bare IGZO-EGFET. Subsequently, IGZO-EGFETs immobilized with a monoclonal antibody were employed for the in situ detection of alpha-synuclein (αS) proteins in concentration ranges from 10 fg mL−1 to 1 ng mL−1. The results showed that IGZO-EGFETs are suitable for the specific recognition of analytes with a linear relationship of 9.35 mV dec−1 between Vth shifts and αS concentrations in a logarithmic scale, verifying its applicability as a sensing device for biological interactions.