Cyclodextrin-decorated Plasmonic Gold Nanosatellite Substrate for Selective Detection of Bipyridylium Pesticides
A cyclodextrin-decorated gold nanosatellite (AuNSL) substrate was developed as a surface-enhanced Raman scattering sensor for the selective sensing of bipyridylium pesticides such as paraquat (PQ), diquat (DQ), and difenzoquat (DIF). The AuNSL structure was fabricated via the vacuum deposition of gold nanoparticles (AuNPs) on a gold nanopillar substrate, and a large density of hot-spots was formed for Raman signal enhancement. Thiolated β-cyclodextrin (SH-CD) was surface-modified on the AuNSL as a chemical receptor. The detection limit of PQ, DQ, and DIF on SH-CD-coated AuNSL (CD-AuNSL) was 0.05 ppm for each, and showed linear correlation in the concentration range of 10 ppm - 0.05 ppm. Then, selective bipyridylium pesticides detection was studied by comparing the Raman intensity of each pesticide with and without the washing step. After the washing step, 90 % of the PQ, DQ, and DIF Raman signals were maintained on the CD-AuNSL substrate with a uniform selectivity in the mapping area of 200 μm x 200 μm. Further, the selective pesticides detection was tested using a grinded-apple solution without pretreatment. Raman signals were clearly observed after the washing step and showed limit of detection down to a concentration of 0.05 ppm for each pesticide. Principal component analysis (PCA) of the binary and ternary mixtures of PQ, DQ, and DIF demonstrated that each component could be easily identified via analysis of the typical Raman fingerprint. The developed CD-AuNSL is expected to be applied for various chemical sensors, especially for pyridine-containing toxic substances in the environment and metabolite biomarkers in biofluids.