On the impedance spectroscopy of field‐effect biosensors

Impedance spectroscopy is an electrochemical technique widely used for the electrical characterization of behavior biomaterials in all kinds biosensors. Field-effect devices, and particular ion-sensitive field-effect transistors (ISFETs), have been extensively studied as transducers biosensing. They however not much analyzed with impedance spectroscopy, because they typically generate non-Faradaic capacitance measurements, since there no charge transfer through insulating gate contact liquid solution. We recently experimentally shown that Faradaic-like spectra can be obtained ISFET allowing high-sensitivity measurements different pH biomarker concentrations. In this paper, we report both well understood by a DC small-signal AC model working conditions. are described operation subthreshold A Nyquist plot semicircle obtained, corresponding to transimpedance 1/gm parallel capacitances. show independent presence membrane material on surface. these conditions, change diameter or concentrations threshold voltage shift transistor. This description illustrated our recent results detection tumor necrosis factor-α functionalized devices standard solutions concentration range 1–20 pg/ml. The use takes advantage exponential gm(VGS) curves (weak inversion) ISFET. large signal amplification, where small spectrum, thus achieving increased precision measurement device response changes analyte concentration.