One-pot preparation of Au-Pt bimetallic single-atom nanozymes with efficient peroxidase-like activity using chitosan and l-tyrosine as carriers for visual and colorimetric detection of quercetin.

An one-pot method was used to prepare bimetallic nanozymes, with chitosan (CS) and l-tyrosine (L-Tyr) as stabilized dispersed colloidal solutions and a carrier for gold-platinum single atoms (Au-Pt SAs), which exhibited excellent peroxidase activity. A colorimetric method based on CS/L-Tyr/Au-Pt SAs nanozymes was constructed for the colorimetric detection of quercetin (QR) in human serum and orange juice. The synthesized bimetallic nanozymes were characterized by SEM, TEM, HAADF-STEM, FT-IR, XRD and XPS techniques to demonstrate the successful synthesis of CS/L-Tyr/Au-Pt SAs nanozymes. Due to the extremely high catalytic activity of the intrinsic active sites of Au-Pt SAs, each site can effectively catalyze the decomposition of HO to produce hydroxyl radicals (·OH), which oxidizes the colorless substrate 3,3',5,5'-tetramethylbenzidine (TMB) to produce a blue product (ox-TMB), and the blue product gradually disappeared after the addition of QR, which indicates that QR can effectively inhibit the TMB oxidation of TMB. In addition, the effect of various experimental conditions on the activity of the nanozymes was investigated to obtain the optimal enzyme activity. The high selectivity of the nanozymes for QR detection was verified by using analogs as interfering agents. The linear range of this colorimetric method for the detection of QR was 0.001-500.0 μM with a detection limit of 0.33 nM. It was successfully used for QR detection in real samples of human serum and orange juice with recoveries of 97.95 %-99.52 % and 97.18 %-105.04 %, respectively, proving its great value for practical applications in biological systems.