Indirect detection of trichlorfon in agricultural products based on Raman silent region

In this study, the copper-based prussian blue analogue coated gold nanoparticles (Au@Cu-PBA NPs) were prepared by simple in situ etching method and firstly applied as surface-enhanced Raman scattering (SERS) tags for indirectly analyzing trichlorfon. The obtained Au@Cu-PBA NPs presented core-shell structure and exhibited an only sharp signal peak at 2175 cm^-1 in Raman silent region. The indirect SERS method was constructed for detecting trichlorfon in agricultural products based on competitive binding between trichlorfon and capture probes (Fe₃O₄@cApt) for signal probes (Au@Cu-PBA NPs@Apt). Under optimized competitive conditions (200 nM Apt, 300 nM cApt, 0.075 mg mL^-1 Fe₃O₄-COOH, 25 min at 35 °C for both incubation and competitive binding), the indirect SERS method showed good linear relationship between relative Raman intensity and logarithm of trichlorfon concentration in the range of 100-10,000 ng mL^-1. The limits of detection were from 16.6 to 22.3 ng g^-1 in cabbage, cucumber, apple and pear. The satisfactory recoveries (82.0%-90.3%) with relative standard deviations of 1.33%-5.95% were achieved. Benefiting from the synergy of specific recognition of trichlorfon by aptamer in binding process and spectral anti-interference of PBA tags in Raman silent region, this proposed method was finally proved to be sensitive, accurate and practical, especially possessing distinct advantages of high selectivity and excellent anti-interference capability for detecting trace trichlorfon in complex agricultural products.