Cu single-atom nanozyme-embedded hydrogel as a portable colorimetric sensor for visual detection of ascorbic acid in food matrices

A Cu single-atom nanozyme Cu/phen-NC is synthesized. • Cu/phen-NC is introduced to a hydrogel to construct a portable colorimetric sensor. • Smartphone-assisted colorimetric sensor for ascorbic acid detection is developed. The rapid and on-site monitoring of ascorbic acid (AA, vitamin C) is crucial for assessing the nutritional quality and freshness of food products. In this work, a portable colorimetric sensor is developed by embedding a Cu single-atom nanozyme (Cu/phen-NC) within a polyacrylamide-gelatin hydrogel for smartphone-assisted detection of ascorbic acid (AA) in foods. Cu/phen-NC, synthesized using 1,10-phenanthroline and urea dual-ligands, exhibits enhanced peroxidase-like activity. The nanozyme-hydrogel catalyzes the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) by H₂O₂, generating a blue color that fades upon AA addition. Smartphone-captured images are analyzed via ImageJ, establishing a linear relationship between grayscale and AA concentration. The platform achieves detection limits of 0.12 μM and 0.44 μM, with high selectivity and stability. Application to vitamin beverages and oranges yields recoveries of 97.07%–101.32% (RSD ≤ 6.49%). This integrated sensing system offers a cost-effective, user-friendly approach for on-site AA detection, with promising applications in food quality control and nutritional assessment. Schematic illustration of ascorbic acid colorimetric sensing using Cu/phen-NC nanozyme encapsulated in hydrogel versus traditional UV–Vis spectroscopic detection. Download: Download high-res image (112KB) Download: Download full-size image