A portable paper-based analytical device mediated by transition metal selenide nanozymes based on Hg2+-activated oxidase-like activity

Schematic diagram of the synthesis of CoSe 2 and the detection of Hg 2+ by colorimetric and smartphone-based test strip platforms. • Six transition metal selenide nanozymes with Hg 2+ -responsive oxidase-like activity were successfully synthesized. • Hg 2+ activated the oxidase-like activity of transition metal selenide nanozymes due to the formation of Hg-Se bonds. • A dual-mode platform of colorimetric and smartphone-based portable test strips was constructed for Hg 2+ detection. • Portable test strips enable qualitative semi-quantitative screening for on-site Hg 2+ in just 2 min. The booming development of nanozymes opens up great prospects for multimodal analysis of Hg contamination scenarios. However, most nanozymes with ideal performance have complex surface modification procedures. The resulting defects, such as the masking of the active site and low binding efficiency to the target, have hindered their application in the Hg 2+ detection field. To this end, six transition metal selenide (TMS) nanozymes (CoSe 2 , NiSe 2 , MoSe 2 , WSe 2 , MnSe, and CuSe) with Hg 2+ -responsive oxidase-like (OXD-like) activity were successfully synthesized utilizing the efficient biomimetic design of the nanozymes in this study. Furthermore, the Hirshfeld charge and formation energy of the TMS-Hg 2+ reaction were investigated using density functional theory (DFT). The calculation and analysis of charge density differences revealed the electron transfer pathways and flow direction during the binding and electron coupling of Hg-Se bonds. Therefore, the mechanism of the enhanced TMS-Hg 2+ OXD-like activity (which accelerates electron transport in the system due to the generation of electron transfer channels by the Hg-Se bond) was clarified, and the ideal TMS nanozyme (CoSe 2 ) most sensitive to Hg 2+ was determined. On this basis, a dual-mode analysis system for Hg 2+ detection by solution colorimetry and smartphone-based portable test strip platform was developed and effectively utilized to assay Hg 2+ in lettuce spiked samples, reducing the detection time to 2 min. Therefore, this study provides valuable insights into the efficient biomimetic recognition design of nanozymes and the application of cost-effective and real-time detection in mercury contamination scenarios.