Enhancement of sensitivity in SPR detection of fipronil based on an Fe₃O₄@PDA signal amplification strategy

The detection of fipronil (FPN), a widely used insecticide, in environmental and food matrices is crucial owing to its possible harmful repercussions on human health and ecological systems. This study introduces an innovative signal amplification strategy employing Fe₃O₄@polydopamine (Fe₃O₄@PDA) nanoparticles to substantially augment SPR sensitivity in FPN detection and enhance the overall detection performance. Utilizing an indirect competitive inhibition assay, we constructed a sensing platform in which antigens were immobilized on a PDA-modified gold film integrated with reduced gold nanoparticles (AuNPs). Concurrently, fipronil antibodies (FPN-Ab) were conjugated to Fe₃O₄@PDA, forming magnetic immunoprobes that facilitate the precise capture, magnetic separation, and enrichment of FPN. This methodology achieved a limit of detection (LOD) of 0.52 nM and a half-maximal inhibitory concentration (IC₅₀) of 30.10 nM within a linear range of 18.3-146.4 nM. Experimental results validated the method's efficacy in quantifying FPN residues in real samples, including milk and tap water, demonstrating excellent repeatability and specificity. These findings underscore the potential of the Fe₃O₄@PDA-based SPR platform as an ultrasensitive and dependable means for FPN detection in diverse environmental and food matrices, addressing the critical need for accurate and efficient monitoring of pesticide residues.