Abstract: A colorimetric method for the rapid detection of hypoxanthine (Hx) content in fish was established using copper nanoclusters (CuNCs) with high intrinsic peroxidase-like activity. Cysteine-stabilized CuNCs were prepared by a simple stirring method at room temperature. The morphology, elemental composition, surface functional groups and luminescence property of Cys-CuNCs were characterized by transmission electron microscopy (TEM), photoelectron spectroscopy, Fourier transform infrared spectrometer (FTIR) spectroscopy and fluorescence spectroscopy, respectively. Ultraviolet-visible spectroscopic experiments showed that Cys-CuNCs sensitively catalyzed the oxidation of 3,3’,5,5’-tetramethylbenzidine by H2O2, allowing for the colorimetric sensing of H2O2 content. On this basis, a colorimetric assay for Hx determination was established by generating H2O2 under the catalysis of xanthine oxidase. Under the optimal conditions as follows: incubation temperature 30 ℃ and incubation time 1 h, good linearity between Hx concentration in the range of 4–100 μmol/L and absorbance was observed and the detection of limit was 1.2 μmol/L. Finally, the proposed method was applied to the determination of Hx content in fish, and the freshness of fish was judged by establishing its correlation with total volatile basic nitrogen (TVB-N) content.

Key words: hypoxanthine; copper nanoclusters; enzyme mimetic activity; hydrogen peroxide; freshness