Construction of Fe₃O₄@Au-Based Fluorescence-Colorimetric Aptasensor for Acetamiprid Assay

Acetamiprid (ACE) residues in vegetables from long-term pesticide use pose potential toxicity risks to human health. Therefore, simple and accurate methods for ACE detection are essential for food safety. In this study, a dual-mode aptasensor was developed based on the specific recognition of fluorescent aptamers (Apts-FAM) combined with the fluorescence quenching and peroxidase-mimicking catalytic properties of Fe₃O₄@Au nanocomposites. The optimal conditions (quenching concentration/time, ACE incubation time) were determined. Under optimized conditions, a linear relationship between ACE concentration (0.5-10 µg/mL) and both fluorescence intensity change (ΔF) and absorbance (A) was established. The fluorescence calibration curve was ΔF = 373.621 C + 5406.812 (R² = 0.9940) with a detection limit (LOD) of 0.416 µg/mL(0.25 mg/kg). The colorimetric response was A = 0.03344 C + 0.10842 (R² = 0.9965) with an LOD of 0.485 µg/mL(0.29 mg/kg). Specificity tests showed no significant cross-reactivity with four structural analogs (dinotefuran, thiamethoxam, imidacloprid, nitenpyram). Reproducibility tests (five replicates at 10 µg/mL ACE) gave relative standard deviations below 8% for both detection modes. In real vegetable samples (Chinese cabbage and cucumber), recovery rates for fluorescence signals ranged from 84.07% to 95.83% (CV ≤ 9.56%), and for colorimetric signals from 80.56% to 91.81% (CV ≤ 7.18%), confirming strong anti-matrix interference capability. These results demonstrate that the dual-signal aptasensor offers good sensitivity and accuracy, making it suitable for practical ACE residue analysis in vegetables.