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 S 2− and Fe 2+ detection in complex agricultural products, ultra-small nano CeO 2 /CuO doped carboxylated chitosan fibers (CeO 2 /CuO CCF) was constructed under microwave-assisted conditions. Not only did CeO 2 /CuO CCF possess suitable BET specific surface area, superior stability and synergistic-enhancement oxidase-like activity, trace S 2− or Fe 2+ 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( A 729 / A 343 )/lg( A 415/ A 343 ) and c S 2− or c Fe 2+ with large linear ranges. When applied for visual monitoring of S 2− and Fe 2+ 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 CeO 2 /CuO CCF to selectively recognize S 2− and Fe 2+ were proposed. This work will provide an efficient way for visual monitoring of multiple analytes in complex agricultural products.