Functionalized single ZnO-metal junction as a pH sensor

Abstract

We have prepared a novel pH sensor consisting in single ZnO micro-wire (MW) aligned on gold-electrode array prepared by electromigrating eight parallel gold wires on silicon wafer with a custom electronic system, leading to nano-sized gap. We also anchored to the ZnO MW surface organic functional molecules rich of amine (-NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) groups, thus ZnO-NH The MWs were then deposited from solution and oreinted through dielectrophoresis, resulting in eight single MWs aligned across the electromigrated gold electrodes. Therefore each single silicon chip is composed by eight separated pH sensors. We measured the I-V characteristic and secondly the ZnO MW Field Effect Transistor (MW-FET) to evaluate the sensitivity of both amine-functionalized and unfunctionalized ZnO-gold junctions upon a pH variation to both acidic and basic values of the solution environmentWe show the superiority in pH response of the ZnO-NH junctions, with an increase of one order of magnitude of the current during the pH reduction, with respect to the bare ZnO ones. In particular a strong sensitivity enhancement was measured by MW-FET with respect to conventional I-V characteristics.