Ultra-small nano CeO2/CuO doped carboxylated chitosan fibers for high-performance oxidase-mimic visual monitoring of S2− and Fe2+ in agricultural products

To improve the sensitivity and selectivity for S2− and Fe2+ detection in complex agricultural products, ultra-small nano CeO2/CuO doped carboxylated chitosan fibers (CeO2/CuO CCF) was constructed under microwave-assisted conditions. Not only did CeO2/CuO CCF possess suitable BET specific surface area, superior stability and synergistic-enhancement oxidase-like activity, trace S2− or Fe2+ could selectively change its oxidase-like activity accompanying with visible color changes. Under the optimized conditions, there express specific double ratiometric colorimetric linear relationships between lg(A729/A343)/lg(A415/A343) and cS2− or cFe2+ with large linear ranges. When applied for visual monitoring of S2− and Fe2+ in real agricultural products, the detection limits were low to 3.5 × 10−9 mol·L−1 and 9.4 × 10−8 mol·L−1 respectively, far below the permitted values in drinking water by World Health Organization. The mechanisms for synergistic-enhancement oxidase-like activity for CeO2/CuO CCF to selectively recognize S2− and Fe2+ were proposed. This work will provide an efficient way for visual monitoring of multiple analytes in complex agricultural products