A Sensitive Label-Free Nanopipette Aptasensor for Acetamiprid Detection in Food Samples Based on Target-Triggered AuNPs@cDNA Probes

The target-induced strand displacement approach has demonstrated effective performance in small-molecule detection through competitive binding involving the target, its specific truncated aptamer, and the complementary DNA. Here, a straightforward label-free nanopipette aptasensor was developed to detect acetamiprid (ACE) residues efficiently, a widely used insecticide, in vegetable crops for pest treatment. This aptasensor was designed using an ACE-specific truncated aptamer immobilized on magnetic beads through biotin–streptavidin interaction, along with its specifically optimized partially complementary polyadenine DNA (polyA cDNA) functionalized on gold nanoparticles (AuNPs@cDNA). This polyA-rich region serves as an anchoring block to ensure the adsorption onto the AuNP surface, thereby promoting the aptamer–cDNA complex formation. The addition of the ACE target will lead to the release of the AuNPs@cDNA strand owing to the robust interaction between the target and its corresponding aptamer. Under the optimized experimental conditions, the proposed aptamer-based nanopipette sensor exhibited outstanding linearity with acetamiprid concentrations ranging from 1.0 × 10 –1 to 100.0 ng mL –1, achieving a detection limit of 1.0 × 10 –1 ng mL –1 within an overall assay time of 30 min (detection stage). In addition, this strategy demonstrated significant selectivity in detecting acetamiprid in complex samples among nontarget interfering substances. Interestingly, the nanopipette aptasensor effectively detected ACE residues in spiked spinach and lettuce extracts, with recoveries ranging from 97.76% to 101%, comparable to the results obtained from LC-MS/MS analysis, emphasizing its capabilities as an ultrasensitive detection tool in food safety.