ZnO-co-CeO2 decorated chitosan fiber oxidase mimic identified for visual monitoring of NO2−, S2− and Fe2+ in food

Abstract

Food safety and protection is one of the key research hotspots nowadays. To recognize toxic NO₂⁻/S²⁻ and ultra-trace Fe²⁺ in food, nano ZnO-co-CeO₂ decorated chitosan fiber (CeO₂/ZnO@CC) was identified using microwave-assisted hydrothermal methods. Not only did CeO₂/ZnO@CC possesses synergistic-enhancement oxidase-like activity (K_m/V_max for catalyzing the oxidization of 3,3’,5,5’-tetramethyl benzidine (TMB) were 0.0212 mM/5.045 × 10⁻⁸ M·s⁻¹), trace NO₂⁻, S²⁻ or Fe²⁺ could selectively make the color of CeO₂/ZnO@CC-TMB changed with obvious hyperchromic or hypochromic effect. Under the optimized conditions, there were excellent linear relationships between A₆₅₅ and c_NO2⁻, c_S²⁻ or c_Fe²⁺ with detection limits of 6.63 × 10⁻⁸ M, 9.83 × 10⁻⁹ M and 5.1 × 10⁻⁸ M, far below their permitted values in drinking water made by World Health Organization (WHO). When applied for visual monitoring of NO₂⁻/S²⁻/Fe²⁺ in food samples, the recoveries (%) were 98.5∼103.4 %/ 97.7∼100.6 %/ 98.6∼104.5 % respectively. The mechanisms for oxidase-like activity and NO₂⁻/S²⁻/Fe²⁺ recognition were also confirmed. This work will offer a promising way for visual monitoring of NO₂⁻, S²⁻ or Fe²⁺ in complex food samples by virtue of enzyme-like signal amplification.