Au nanoparticles decorated covalent organic framework composite for SERS analyses of malachite green and thiram residues in foods

A three-dimensional (3D) surface-enhanced Raman scattering (SERS) substrate composed of gold nanoparticles (AuNPs) self-assembled covalent organic frameworks (COFs) was fabricated via the electrostatic interaction between positively charged COFs and negatively charged AuNPs, which exhibited excellent SERS performance and were successfully applied for the analyses of malachite green (MG) residue in different seafood products as well as thiram residue in several kinds of fruit juice. The raspberry-like structure SERS substrate has a larger surface area that can provide more adsorption sites in testing and improve the efficiency of sample enrichment. By using this developed SERS substrate, the detection linearity ranges are 1.0 × 10−9 mol·L−1–1.0 × 10−6 mol·L−1 for MG and 5.0 × 10−8 mol·L−1–1.0 × 10−5 mol·L−1 for thiram (R2 ≥ 0.995). The detection limits are 6.2 × 10−10 mol·L−1 for MG and 1.7 × 10−8 mol·L−1 for thiram, respectively. The COF-AuNPs substrate was actually applied for analysis of MG in seafood products and thiram in different fruit juice, with the recoveries in the ranges of 94.67–108.99 % for MG and 95.00–107.58 % for thiram, and both of the relative standard deviation (RSD) are no more than 5.88 %. This work indicates that the developed COF-AuNPs substrate is promising for SERS analyses and detections of residues in foods.