Titanium Carbide MXenes Mediated In Situ Reduction Allows Label-Free and Visualized Nanoplasmonic Sensing of Silver Ions

The label-free assay has drawn extensive attention because it does not require a labeling step and enables direct interaction and signal transduction between the sensing unit and target analytes. Herein, we demonstrate a proof-of-principle concept of a label-free and visualized nanoplasmonic strategy for silver ions sensing, where only Ti₃C₂ MXenes are employed by exploring their excellent adsorption affinity and reductive property toward metal ions. Ag⁺ was adsorbed onto the surface of Ti₃C₂ MXene nanosheets, followed by the Ti₃C₂ MXenes mediated in situ silver nanoparticles (Ag NPs) generation without adding any extra stabilizing or reducing agent. The excellent localized surface plasmon resonances at a particular wavelength provide Ag NPs the capability for colorimetric assay with a detection limit of 0.615 μM. With the assistance of a smartphone, RGB analysis exhibited visualized results consistent with the results measured on a UV–vis spectrometer, promising a budget, simple-operating on-site detection. Moreover, the detection of Ag⁺ in real samples was achieved with satisfactory results meeting the analysis demand for the Drinking Water Standards of the World Health Organization (WHO) and the United States Environmental Protection Agency (U.S. EPA). These results reveal that Ti₃C₂ MXenes possess great potential in building convenient label-free colorimetry nanoplatforms and may evoke more inspirations to explore strategies for the direct sensing of analytes.