Rapid detection of thiram on apple surfaces using a flexible and sticky SERS substrate coupled with chemometric methods

In this paper, we developed a simple, rapid and sensitive method for detection of thiram on apple surfaces by surface enhance Raman spectroscopy (SERS) combined with chemometric methods. Ag NCs (Ag nanocubes) were firstly prepared by a sulfide-mediated polyol method. Then the flexible and adhesive Ag NCs@PDMS substrates were obtained by combining Ag NCs self-assembled films with PDMS films. Thiram residues on apple surfaces were transferred to the substrate using adhesion properties of Ag NCs@PDMS. And the SERS spectra were obtained by Raman microscopy and analyzed with chemometric methods. The results were analyzed by principal component analysis (PCA), for the limit of detection (LOD) of thriam on apple surfaces was 0.01 ppm. Principal component regression (PCR) and partial least squares regression (PLSR) were explored to develop quantitative models. Both models represented higher correlation coefficients (close to 1), but PLSR models exhibited better predictive performance, with the correlation coefficient was 0.99282 with a low root mean squared error of calibration (RMSEC = 0.438) and root mean squared error of validation (RMSECV = 0.597). The developed SERS method based on Ag NCs@PDMS substrate provide a simpler and more sensitive way to monitor thiram on apple surfaces.