Boronic acid ester-based hydrogel as surface-enhanced Raman scattering substrates for separation, enrichment, hydrolysis and detection of hydrogen peroxide residue in dairy product all-in-one.

Rapid and selective separation, enrichment and detection of trace residue all-in-one in complex samples is a major challenge. Hydrogels with molecular sieve properties can selectively separate and enrich target analytes, and the combination with high sensitivity detection of surface-enhanced Raman scattering (SERS) is expected to achieve the above all-in-one detection. Herein, the core-shell structured Au@poly(N-isopropylacrylamide)-phenylboronic acid hydrogel (Au@PNIP-VBA) with boronic acid ester groups was prepared by thermally initiated polymerization. The boronic acid ester groups in hydrogel are selectively hydrolyzed by hydrogen peroxide (H₂O₂) to hydroxyl structures, leading to a reduction in SERS signals. The Au@PNIP-VBA hydrogel has molecular sieve properties and high SERS activity, making it suitable for separation, enrichment, hydrolysis and detection of H₂O₂ all-in-one. A rapid SERS method was developed for analysis of H₂O₂ based on the Au@PNIP-VBA hydrogel with the linear range of 8.5 × 10^-2-6.8 mg L^-1 and the detection limit of 33 μg L^-1. The method was successfully applied to the determination of H₂O₂ residue in fresh milk, pure milk, yogurt and camel milk, with the recoveries were in the range of 82.2%-109.3% and the relative standard deviations were 2.8%-8.3%. This efficient all-in-one strategy has the advantages of simple sample pre-treatment, rapid analysis (30 min) and high sensitivity, making it highly promising for food quality and safety analysis.