Sulfhydryl functionalization of MXene enables selective sensing of mercury ions

Abstract

Mercury toxicity is a serious concern because even at low concentrations, it can enter the human body through fish consumption, leading to alarming health effects. Inspired by how mercury finds its way (binds) through easy targets, -sulfhydryl groups in living systems, we have functionalized MXene (a 2D transition metal carbide renowned for its high conductivity and extensive surface area) with glutathione (a thiol-containing tripeptide), to facilitate free SH binding sites for mercury ion (Hg²⁺) detection. The same functionalization to graphene oxide failed, as glutathione (GSH) binds to the graphene surface through –SH unlike MXene which binds through –NH, thus facilitating free SH for mercury binding and enabling its detection. The electrochemical performance of the sensor is systematically investigated using cyclic voltammetry and differential pulse voltammetry techniques. The MXene–GSH sensor exhibits exceptional sensitivity of 0.1971 μA M⁻¹ cm⁻² and selectivity for mercury ions, demonstrating a broad linear detection range spanning from 140 to 540 nM and an impressively good detection limit of 1.16 nM (0.232 ppb). The quick response of the developed probe at 500 ms (0 min) towards Hg²⁺ indicates the strong affinity unlike the existing probe, which required pre-depositions, thus providing a robust and efficient tool for the expeditious detection of mercury. The amalgamation of MXene's inherent conductivity and glutathione's specific affinity for mercury ions contributes to the sensor's efficacy, particularly at low concentrations, and still remains a challenge.