Microfluidics integrated NiO based electrolyte-gated FETs for the detection of cortisol

Abstract

Field effect transistors (FETs) have emerged to be an attractive platform for the accurate and rapid detection of biological moieties. The gating effect in a FET when applied through an electrolyte further improves the device sensitivity and response time. The present work involves two aspects for devising an electrolyte-gated FET (EGFET) based platform for the detection of cortisol. The former involves optimization of the semiconducting channel dimensions and its deposition parameters to achieve maximum sensitivity of the device. Afterwards, the optimized device has been integrated with appropriate microfluidic channels for reliable and rapid detection using low sample volumes. A nickel oxide (NiO) thin film has been used as a semiconducting channel and sensing layer. The device has been electrically and structurally characterized and the cortisol sensing performance has been analyzed by binding cortisol antibodies to NiO covalently. A microfluidic system has been optimized for analyte delivery. High sensitivity in a wide linear range of cortisol antigen concentrations from 1 fg mL⁻¹ to 1 μg mL⁻¹ with a low detection limit of 0.5 fg mL⁻¹ and a stability of 7 weeks shows the applicability of the devised structure for point-of-care applications. The final device structure has been analyzed on real saliva samples and the results are found to be in good agreement with the standard ELISA.