Comparing the performances of electrochemical sensors using p-aminophenol redox cycling by different reductants on gold electrodes modified with self-assembled monolayers

p-Aminophenol (p-AP) redox cycling using chemical reductants is one strategy for developing sensitive electrochemical sensors. However, most of the reported reductants are only used on indium-tin oxide (ITO) electrodes but not gold electrodes due to the high background current caused by the oxidation reaction of the reductants on the highly electrocatalytic gold electrodes. Therefore, new strategies and/or reductants are in demand for expanding the application of p-AP redox cycling on gold electrodes. In this work, we compared the performances of several reductants in p-AP redox cycling on self-assembled monolayers (SAMs)-modified gold electrodes. Among the tested reagents, nicotinamide adenine dinucleotide (NADH), tris(2-carboxyethyl)phosphine (TCEP) and cysteamine were demonstrated to be suitable for p-AP redox cycling on the alkanethiol-modified gold electrodes because of their low background current. The rate of chemical reaction between reductants and p-quinone imine (QI, the electrochemically oxidized product of p-AP) increases in the order of NADH < TCEP < cysteamine. The system benefits from the low background current, fast chemical reaction and amenability and sensitivity of the sensor with TCEP or cysteamine as the reductant; these performance enhancements were demonstrated by the detection of microRNA. A detection limit of 2 pmol L−1 was achieved. We believe that our work will be valuable for the development of electrochemical sensors using p-AP redox cycling on gold electrodes.