Comparative Assessment of Gold and Carbon Nanoparticles as Tags for Lateral Flow Immunoassay of Fenpropathrin in Green Tea.

Fenpropathrin (FPT) residues in tea pose a threat to consumers' health. Lateral flow immunoassay (LFIA) offers a rapid and convenient approach for FPT detection. However, existing LFIA formats, particularly those employing fluorescent nanoparticles, are susceptible to interference from the tea matrix's endogenous fluorescence, limiting their accuracy for FPT analysis. Here, two complementary LFIAs based on gold nanoparticle (AuNP) and carbon nanoparticle (CNP) tags were developed, both of which avoid matrix fluorescence effects due to their intrinsic coloration under ambient light. We systematically evaluated five cleanup materials and identified polyvinylpolypyrrolidone as the optimal cleanup material. Following PVPP-based purification, green tea extracts required only a four-fold dilution prior to LFIA analysis, effectively minimizing matrix interferences, such as tea polyphenols, and enhancing assay robustness and sensitivity. The visual limit of detection was 0.64 μg/g and a quantitative limit of detection (qLOD) was 0.11 μg/g for FPT in green tea using the AuNP-based LFIA. The CNP-based LFIA further improved sensitivity, with a visual limit of detection of 0.16 μg/g and a qLOD of 0.017 μg/g, a 6.4-fold enhancement in qLOD compared to the AuNP assay. Together, these two assays provide an efficient and accurate strategy for on-site screening of FPT residues in green tea.