Graphene field-effect transistors array for detection of liquid conductivities in the physiological range through novel time-multiplexed impedance measurements

Abstract

In medical applications, graphene field-effect transistors (GFETs) have been employed as sensors for the detection of biological biomarkers and other compounds due to graphene's high sensitivity towards immobilized molecules at its surface. Commonly, the resistivity of a graphene channel is measured under direct drain-source current (DC) and gate voltage sweep. However, like other materials, the electrical response of graphene can also be studied in the form of impedance measurements using alternating drain-source current (AC), which alters the distribution and migration of ionic species across the graphene channel. In this study, an array with 12 non-functionalized GFETs is used for pioneering electrical measurements of prepared liquid solutions in the DC and AC regimes of stimulation. In particular, the transistors were characterized under saline solutions with conductivity levels ranging from 84 μS/cm to 1413 μS/cm. We first report the observation of a larger variation on the graphene's charge neutrality point in gate sweep for the AC regime with varying conductivity levels (ΔVGS = −0.00033∗ΔS) as compared to DC (ΔVGS = −0.00023∗ΔS), which can potentially be explored as a novel way of detecting electrical changes on graphene induced by physiological solutions, chemical analytes, immobilized substances, or cell substrates, when direct current cannot penetrate and influence these structures.