PtNPs/Ti₃C₂T_xNR Nanozyme-Enabled Portable Colorimetric Platform for Ultrasensitive Hexavalent Chromium Monitoring

Hexavalent chromium (Cr⁶⁺) is a persistent pollutant in industrial wastewater, and its detection remains challenging due to the inherent limitations of conventional methods in sensitivity, field applicability, and cost. To overcome these challenges, we established a highly sensitive colorimetric sensing system based on a rationally designed nanocomposite material. Surface-reactive Ti₃C₂T_x nanoribbons (Ti₃C₂T_xNR) were successfully synthesized by controllable alkaline treatment of Ti₃C₂T_x nanosheets, followed by the deposition of platinum nanoparticles to form PtNPs/Ti₃C₂T_xNR hybrids with peroxidase-like catalytic activity. The detection mechanism of this system is based on the competitive interaction between Cr⁶⁺ and 8-hydroxyquinoline (8-HQ), which regulates the colorimetric response of 3,3',5,5'-tetramethylbenzidine (oxTMB). The colorimetric system exhibits a good linear response in the concentration range of 5 nM to 10 µM, with a detection limit of 0.52 nM, demonstrating excellent sensitivity. Importantly, to enhance the applicability for on-site detection, a paper-based platform was further developed, which maintains high sensitivity while offering portability, rapid response, and visual readout. Compared with traditional instrument-dependent methods, this platform generates a concentration-dependent colorimetric response visible to the naked eye and offers significant advantages in simplifying operation, reducing detection costs, and improving field applicability, providing a practical and effective solution for the efficient detection of Cr⁶⁺.