Ultrasensitive detection of imidacloprid in fruits and vegetables using a lateral flow immunoassay based on highly luminescent Au nanoclusters.

In this work, a highly sensitive lateral flow immunoassay (LFIA) strip based on luminescent green-emitting gold nanoclusters (AuNCs) was developed for ultrasensitive and facile visual determination of imidacloprid (ICP). Specifically, the structurally ordered AuNCs system, constructed through 6-aza-2-thiothymine (ATT) as the coordinating ligand and L-arginine (Arg) as the guest molecule (denoted as Arg/ATT/AuNCs), exhibited enhanced and persistent fluorescent emission characteristics. Furthermore, the presence of unbound carboxyl moieties on the Arg/ATT/AuNCs complex facilitated the conjugation with biomolecules, thereby providing a functional indicator for the biosensor assembly. The developed strips operate on the principle of an indirect competitive assay and are capable of effectively detecting target samples in less than 12 min. Moreover, the sample only needs to undergo simple crushing and filtration. The assay provides qualitative results through visual inspection under a UV lamp and quantitative analysis via a portable fluorescence reader. The visual limit of detection (vLOD) was 7.5 ng/mL and the limit of detection (LOD) is 0.026 ng/mL. Additionally, the average recoveries of ICP from apples, oranges, cucumbers, and cabbages samples ranged from 78.0% to 104.8%, 82.0% to 99.1%, 94.0% to 99.1%, and 93.0% to 101.9%, respectively, with relative standard deviations less than 10%. Given its ultrasensitive luminescence performance, the AuNCs-LFIA strip offers great potential for rapid, sensitive, and cost-effective detection of analytes in food safety monitoring.