Substrate-gate coupling in ZnO-FET biosensor for cardiac troponin I detection

Currently, field-effect transistor (FET)-based biosensors have been implemented in several portable sensors with the ultimate application in point-of-care testing (POCT). In this paper, we have designed substrate-gate coupling in FET-based biosensor for the detection of cardiac troponin I (cTnI) biomarker. In the device structure, zinc oxide nanoparticles (ZnO-NPs) thin film were deposited through solgel and spin coating techniques on the channel. The p-type silicon was used as a substrate, while ZnO is an n-type nanomaterial, thus creates p-n-p junction between source, channel, and drain. The deposited thin films exhibited hexagonal wurtzite phase of ZnO, suitable for biomolecular interaction as revealed in X-ray diffraction (XRD) analysis. The surface of the thin film was then functionalized with 3-aminopropyltriethoxysilane (APTES), followed by glutaraldehyde (GA) as a bi-functional linker to immobilize the cTnI monoclonal antibody (MAb-cTnI) as bio-receptor for capturing cTnI biomarker and proven by the Fourier transform-infrared (FT-IR) spectra. Lastly, we demonstrated a new strategy, the integration of FET-based biosensors with substrate-gate showed differences between before (immobilization) and after cTnI target biomarker interaction by significant changes in drain current (la) and change of threshold voltage (VT), which improved the sensitive detection, with the limit of detection down to 3.24 pg/ml. (C) 2016 Elsevier B.V. All rights reserved.