Dual-Function Colorimetric Platform for Hg2+ Detection and Cys/Hcy Discrimination Based on the Peroxidase-Like Activity of CuAu Nanozymes

Abstract

This study presents a colorimetric method for the detection of Hg2+ and discrimination of cysteine(Cys) and homocysteine(Hcy) based on the peroxidase(POD)-like activity of copper-gold nanoparticles (CuAuNPs). CuAuNPs with an average size of approximately 15 nm were synthesized via a one-step reduction method and exhibited intrinsic POD-like activity, catalyzing the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H2O2 to produce a blue-colored product with a characteristic absorbance at 652 nm The addition of Hg2+ specifically enhances the catalytic activity of CuAuNPs, resulting in a distinct color change of the TMB–H2O2 solution from light blue to dark blue. Conversely, introduction of Cys or Hcy leads to competitive binding between their thiol (-SH) groups and Hg2+, forming stable S-Hg complexes, resulting in a concentration-dependent fading of the blue color. The distinct suppression extents between Cys and Hcy enable their discrimination. Under optimized conditions, the method enables quantitative detection of Hg2+ in the range of 100-900 nM (R2=0.990) with a detection limit of 10 nM, and achieves satisfactory recoveries of 90.4%-110.2% in spiked emollient water samples. For Cys and Hcy, linear responses are obtained over 5-40 µM (R2=0.991; LOD=2.5 µM) and 6-50 µM (R2= 0.992; LOD=2.3 µM), respectively. The assay was successfully applied to rat serum samples, yielding recoveries of 99.4%-108.1%（RSD＜6.2%）for Cys and 95.0%-104.1%（RSD＜6.4%）for Hcy. The proposed method is simple, rapid, and selective, offering a promising nanozyme-based platform for environmental monitoring and biomedical diagnostics.