Au Nanoparticle-Based Surface-Enhanced Raman Spectroscopy Aptasensors for Paraquat Herbicide Detection

Herein, we developed a surface-enhanced Raman spectroscopy (SERS)-based aptasensor platform by modifying gold (Au) nanoparticle SERS substrates with a thiol-containing aptamer for sensitive and selective detection of paraquat (PQ), a commonly used herbicide for weed and grass control. The Au nanoparticle SERS substrate used in this study is a commercial SERS substrate (ONSPEC-Lite, https://www.nectec.or.th/en/innovation/product-innovation/onspec-series.html ) developed by our group at NECTEC, Thailand. The average size of the nanoparticle is 59 ± 17 nm. A thiol-modified aptamer PQ77-SH was immobilized on the Au nanoparticle surface and used as a bioreceptor for binding the PQ molecules selectively on the SERS substrate. PQ detection in water medium using the SERS-based aptasensor substrates was carried out by observing the Raman peak intensities of PQ at different concentrations and compared with SERS substrates without aptamer modifications. Modification of the SERS substrates with aptamers improves the sensitivity and enables selective detection of PQ with a limit of detection estimated to be 0.10 ± 0.03 μM. The developed SERS-based aptasensor platform was evaluated using natural water samples collected from a nearby pond and demonstrated good stability against interferences from other similar herbicides and insecticides present along with PQ in water. The findings of this study indicate that the SERS-based aptasensor not only increases the sensitivity of SERS substrates but also, and this is crucial, makes them selective toward PQ detection, assisting in resolving the problem of low selectivity from conventional SERS substrates.