Determination of polyphenols in fruits based on metal-polyphenol coordination and surface-enhanced Raman scattering...

Polyphenols, as the predominant natural antioxidants in fruits, are key indicators of nutritional value. However, conventional polyphenol assays involve complex pretreatment and rely on their reducing properties, making them susceptible to interference and limiting sensitivity. Therefore, it is crucial to develop a simple and sensitive method for polyphenols detection.

Herein, core-shell metal-organic framework nanomaterials (AuNR/PATP@ZIF-8) were constructed by in situ growth of zeolitic imidazolate framework-8 (ZIF-8) on gold nanorods/p-aminothiophenol (AuNRs/PATP). Surface-Enhanced Raman Scattering (SERS) was obtained utilizing the enrichment effect of ZIF-8 on small molecules and the chemical enhancement effect of ZIF-8 on gold nanorods (AuNRs). The polyphenols were sensitively detected based on the coordination of polyphenols with Zn²⁺ using SERS. Gallic acid (GA), tannic acid (TA) and piceatannol (PIC) were detected as model polyphenols. The limit of detection (LOD) of GA, TA and PIC were 0.69 nM, 0.48 nM and 0.64 nM, and their linear ranges were 1 × 10^-9 - 2 × 10^-6 M, 1 × 10^-9 - 2 × 10^-6 M and 1 × 10^-9 - 1 × 10^-5 M, respectively, which was better than most of the previously reported works. Moreover, the method showed good reproducibility, stability and selectivity and was successfully applied to the evaluation of total polyphenols in grapes.

This method enables highly sensitive detection of polyphenols without complex pretreatment. This method was applied to the detection of total polyphenols in grapes with a wider linear range and higher sensitivity than that of the traditional folin-ciocalteu (F-C) detection, which has great potential in the trace detection of total polyphenols in fruits.