Bioenzyme-free dual-mode sensing: Fe-N/C single-atom nanozyme integrated smart hydrogel for visual detection of carbosulfan

Quick and sensitive monitoring of Carbosulfan (CBF) residues in food is of great significance to guarantee food safety. This study developed a simple, portable, and enzyme-free sodium alginate hydrogel probe (SA-Hydrogel probe) for the colorimetric and fluorescent rapid detection of CBF. Iron single-atom nanozyme (Fe-N/C SANs) with excellent oxidase-like activity was synthesized via high-temperature pyrolysis, which catalyzed the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) into a blue product (oxTMB). Red-emissive carbon dots (R-CDs) with aggregation-induced emission property were introduced as a reference signal, and the generated oxTMB quenched the red fluorescence of R-CDs through the inner filter effect (IFE). However, acidified CBF inhibited the enzyme-like activity of Fe-N/C SANs by producing reductive sulfide ([SH]), leading to a reduction in oxTMB generation. Additionally, the weakened IFE led to the recovery of R-CDs’s fluorescence. The probe exhibited a good linear response to CBF within the range of 0.05~20 μg/mL, with calculated limits of detection (LODs) of 0.025 μg/mL and 0.012 μg/mL based on the color parameter (G+B)/2 R (colorimetric) and R (fluorescent), respectively. This study not only innovatively constructed an enzyme-free dual-mode sensing platform for the rapid identification of CBF but also provides new insights for the development of portable pesticide residue detection devices. • A hydrogel probe without biological enzyme achieved rapid carbosulfan detection. • Portable hydrogel enabled visual carbosulfan monitoring in food samples. • Dual-mode fluorescence and colorimetric signals improved detection reliability. • Smartphone-based quantification attained 0.012 μg/mL sensitivity.