Two-dimensional MXene nanosheets (types Ti3C2Tx and Ti2CTx) as new ion-to-electron transducers in solid-contact calcium ion-selective electrodes.

Two kinds of two-dimensional MXene (of type Ti3C2Tx and Ti2CTx) nanosheets are described for use in solid-contact ion-selective electrodes (SC-ISEs) where they act as ion-to-electron transducers. Electrochemical characterizations show that the MXene-coated electrodes possess high double layer capacitance and enable rapid electron transport. This demonstrates the enhanced efficiency of MXene-based solid-contact layers to improve ion-electron transduction. Both Ti3C2Tx- and Ti2CTx-based SC-ISEs exhibited a Nernstian response (26.4 and 24.9 mV/decade, respectively) between 10-1 and 10-5.5 M Ca(II) concentrations with rapid response (<10 s) and low limits of detection (0.79 μM and 1.0 μM, respectively). The SC-ISEs display a lower charge impedance compared to ISEs without solid-contact layer. The new SC-ISEs possess outstanding potentiometric performance, extraordinary long-term stability, and insensitivity to light, CO2, O2, and redox couples, thus showing great promising prospect for routine sensing applications. Graphical abstractSchematic representation of MXene nanosheets for use as new intermediate layers in solid-contact ion-selective electrodes (SC-ISEs) for the potentiometric detection of calcium ion.