Ion-Sensitive Field-Effect Transistor-Based Biosensors: The Sources of Gates and Their Sensitive Layers—A Review

Numerous techniques, including colorimetric, optical and electrical/electrochemical have been employed in biosensing. The employment of electrochemical technologies, particularly the field-effect transistors (FETs), have been embraced because of their many benefits, including simple design, affordability, a lack of expensive testing equipment, and acceptable findings. There are numerous applications for the ion-sensitive FET (ISFETs) in biology and medicine. Hydrogen peroxide (H2O2), a crucial intermediary in many metabolic and regulatory pathways, glucose, cholesterol, acetylcholine, deoxyribonucleic acid (DNA), cells, and other compounds have been measured using ISFET sensors. In the ISFET structure, due to its proximity to the sensor layer and H2O2, the gate terminal has an undeniable impact on the sensitivity and efficiency of the ISFET-based sensors. Here, we will provide a brief overview of the general characteristics of ISFET before discussing the gate terminal. The structure and composition of the gate surface-sensitive layer as the main factor in determining the sensitivity of ISFET-based sensors will be discussed. We will next review, for the first time, the widely used thin film, nanotubes, nanowires and nanorods, as well as 2-D materials like graphene and molybdenum disulfides as sensitive layer materials.