Transition metal regulation of PtPdCuFe nanozyme with boosted dual enzyme activity for smartphone-assisted colorimetric sensing of nitrite and thiophanate methyl

The detection of thiophanate methyl (TM) and nitrite (NO₂^-) is of great significance for ecosystem and human health. Herein, quaternary PtPdCuFe alloy nanozyme was fabricated by multi-component synergistic strategy. The doping of Cu and Fe could optimize the d-electron distribution of PtPdCuFe nanozyme, further enhancing its oxidase-like (OXD-like) and peroxidase-like (POD-like) activities. Steady-state kinetic analysis of the PtPdCuFe nanozyme reveals that the Michaelis-Menten constants (K_m) of OXD-like and POD-like activities for 3, 3', 5, 5'-tetramethylbenzidine (TMB) are 0.08 mM and 0.09 mM, respectively. Based on the dual enzyme activity of PtPdCuFe nanozyme, selective detection of NO₂^- and TM were realized. NO₂^- detection was carried out using OXD-like activity with linear range of 0.1-150 µM and LOD of 0.054 µM, and TM was recognized by POD-like activity with linear range of 0.1-4 μg/mL and LOD of 0.0646 μg/mL. Additionally, a smartphone-RGB integrated portable platform achieves LOD of 0.085 μg/mL (TM) and 2.15 μM (NO₂^-). The platform also demonstrates its sensing accuracy with recovery rates ranging from 96.25% to 108.27% in environmental and food samples. This work not only provides an effective way to improve the catalytic activity of nanozymes, but also offers a new approach for selective detection of TM and NO₂^- in real samples.