Abstract
A rapid and simple detection method of metolcarb residues in apples with spectral analysis technology was achieved drawing support from the high sensitive and flexible silver/dragonfly wing (Ag/DW) surface-enhanced Raman scattering (SERS) substrates. The three steps “spray”, “press” and “separate” greatly simplified the procedures of extraction and sampling of pesticide molecules, resulting in the entire detection process was completed just in a few minutes. Importantly, the Ag nanoislands offered strong electromagnetic (EM) field enhancement near metallic nanostructures and significantly improved the sensitivity and reproducibility of the Raman signals. Meanwhile, surface plasmon coupling at the nanogaps between adjacent nanoislands created abundant “hot spots”, which became enormous enhancement necessary for high sensitivity SERS detection of metolcarb. Taking the apple peels as carriers, the trace detection of metolcarb residues on them was realized, whose detection limit reached 1×10-9 g/cm2. In addition, the linear relationship (R2 = 0.98666) between the logarithmic concentrations of metolcarb residues and the logarithmic peak areas at 1581 cm-1 was established, which was the more accurate reference for the prediction of the unknown concentration of metolcarb residues. In order to carry out the actual emulation, we studied metolcarb in mixed solution, and its obvious characteristic peaks were observed. These results indicated that SERS technology coupled with “spray-press-separate-test” method had the potential to qualitatively and quantitatively analyse metolcarb residues on complex apple peels.
Highlights
Food safety, as a focus of widespread attention by the whole society, concerns the life safety and physical health of human, in which pesticide residue is an important issue that can not be ignored.[1,2] In the last 10 consecutive years, the Environmental Working Group (EWG) released the list of the most heavily polluted agricultural products, among which apples ranked top
The surface morphologies of natural dragonfly wings and Ag/DW substrates were displayed in Fig. 2, which reflected the distributions and sizes of the sloping pillars on the epicuticular layer of the natural dragonfly wings and the decorated pillars on the surface-enhanced Raman scattering (SERS)-active substrates
Compared with the direct detection of Rhodamine 6G (R6G) solution, the prominent characteristic peaks (1581 cm-1 and 2929 cm-1) of metolcarb were clearly revealed. These results showed that SERS, spectral analysis technology coupled with “spray-press-separate-test” method had great practical value for the detection of pesticides in complex surface system
Summary
It is significative to detect metolcarb residues in complex surface system using a rapid, simple and effective method. The trace detection and quantitative analysis of metolcarb residues on apple peels were successfully achieved using the SERS substrates by a rapid and simple method of “spray-press-separate-test”, which had a certain guiding significance for the practical detection. The determination of metolcarb in mixed solution showed that the analysis of complex apple surfaces with several other substances could be realized using SERS technology, and further demonstrated the potential value of “spray-press-separate-test” method in pesticide detection and food safety evaluation
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