Self-validating photothermal and electrochemical dual-mode sensing based on Hg²⁺ etching Ti₃C₂ MXene

Mercury ions can cause serious damage to the ecological environment, and it is necessary to develop reliable and elegant mercury ion sensors. In this protocol, a label-free photothermal/electrochemical dual-mode strategy for Hg²⁺ is proposed based on delaminated Ti₃C₂ MXene nanosheets (DL-Ti₃C₂ MXene). Hg²⁺ exists in water in the form of HgCl₂, Hg(OH)₂, and HgClOH, and the electron-rich elements O and Cl can specifically bind to the positively charged DL-Ti₃C₂ MXene at the edge, and further oxidation-reduction reaction occurs to obtain TiO₂/C and Hg₂Cl₂. In view of the reduction activity and the performance of photothermal conversion of DL-Ti₃C₂ MXene itself, the electrochemical and photothermal responses decrease with the increase of the logarithm of Hg²⁺ concentration. The corresponding linear ranges are 50 pmol L^-1-500 nmol L^-1 and 1 nmol L^-1-50 μmol L^-1, and their detection limits calculated at 3 S/N are 17.2 pmol L^-1 and 0.43 nmol L^-1, respectively. DL-Ti₃C₂ MXene has the characteristics of a wide range of raw materials, low cost, and easy preparation. In addition, the design takes full advantage of the properties of the material itself, avoids the complex assembly and detection process of conventional sensors, and enables high selectivity and sensitivity for mercury detection. In particular, the dual-mode sensing endows self-confirmation of mercury ion detection results, thereby improving the reliability of the sensor.