Dual-mode nanozyme-hydrogel platform for on-site multi-target detection of biomarkers and hazardous substances

A novel dual-mode sensing system integrating a magnetic core-shell CuFe₂O₄/Cu/MnO₂ nanozyme with a stimuli-responsive agarose-deep eutectic solvent hydrogel (DES-Aga) is reported. The nanozyme exhibits exceptional oxidase-like activity, characterized by a low Michaelis constant (K_m = 0.14 mM) and high catalytic efficiency (V_max = 1.89 × 10^-6 M·s^-1), enabling rapid oxidation of TMB to generate a colorimetric signal. Coupled with the DES-Aga hydrogel, the platform achieves dual-mode detection: laboratory-grade UV-vis quantification (detection limits: 0.01 μM HQ, 0.05 μM GSH, 0.02 μM NO₂^-) and smartphone-assisted on-site analysis. The hydrogel leverages redox/diazotization interactions to produce distinct color transitions (blue → colorless for HQ/GSH; blue → yellow for NO₂^-), validated in real-world matrices (cosmetics, food, serum) with recoveries of 87-115% and RSD < 8.6%. Key innovations include the nanozyme's magnetic recyclability (> 80% activity after 7 cycles), the hydrogel's stability (> 90% retention after 7 days), and a ratiometric strategy for NO₂^- detection. This work bridges the gap between laboratory precision and field-deployable diagnostics, offering a versatile tool for monitoring carcinogens in consumer products, food contaminants, and oxidative stress biomarkers, with direct implications for public health and safety.