Fluorescent Hydrogel Sensor Based upon Polyvinyl Alcohol (PVA), Polyethylene Glycol (PEG), and Aptamer-Functionalized Graphene Quantum Dots (GQDs-Apt) for the On-Site Determination of Acetamiprid Residues in Vegetables

There is a growing concern that residues of agricultural chemicals in fresh produce may pose a risk to public health. Acetamiprid, a broad spectrum insecticide, has attracted increasing attention due to its potential toxicity and environmental persistence. Although conventional analytical techniques offer high accuracy, they are often labor intensive and instrument dependent. To address these limitations, this study aimed to develop a rapid, sensitive, and straightforward method for the detection of acetamiprid residues in leafy vegetables. This study was the first to utilize the water retention property of hydrogels in the detection reaction. The assay could be conducted directly on the vegetable surface without spraying detection reagents. This design greatly simplified the analytical procedure. A fluorescent aptamer based composite hydrogel sensor was successfully fabricated using polyvinyl alcohol (PVA), a polyethylene glycol (PEG) based crosslinked polymer, and aptamer functionalized graphene quantum dots (GQDs-Apt). The composite hydrogel was crosslinked with glutaraldehyde (GA), resulting in a stable three-dimensional network structure with excellent biocompatibility and mechanical strength. The GQDs-Apt conjugates served as the signal reporting units, whose fluorescence characteristics were modulated by the binding interaction between the aptamer and acetamiprid, thereby conferring high sensitivity and selectivity. In the absence of acetamiprid, the aptamer probe remained associated with the graphene quantum dot surface, leading to fluorescence quenching. Upon introduction of the target pesticide, the aptamer preferentially bound to acetamiprid, inducing a conformational change that facilitated detachment of the probe from the quantum dot surface and subsequent fluorescence recovery. This "quenching–recovery" signaling mechanism provided the theoretical basis and practical framework for the quantitative detection of acetamiprid. The fluorescence changes within the hydrogel network were exploited for both the screening and precise quantification of the pesticide. Performance metrics revealed a limit of detection (LOD) of 0.005 μmol L−1, a dynamic range of 0.01 to 10 μmol L−1, and R2 of 0.9971. Validation in real matrices of cabbage, leek and tomato demonstrated robust accuracy and repeatability, with fortified recoveries between 96.11% and 99.47%, relative standard deviation (RSD) below 3.11%, and an equilibration time of less than 20 minutes. This strategy provides a rapid, user friendly, high resolution, and reliable tool for agricultural product safety and environmental monitoring.