Self-assembled Au nanoparticle arrays on thiol-functionalized resin beads for sensitive detection of paraquat by surface-enhanced Raman scattering

Efficient, scalable, and cost-effective self-assembly of Au nanoparticles (NPs) into close-packed arrays on the surfaces of thiol-functionalized resin spheres under mild conditions was demonstrated. The resulting Au NPs–resin spheres possessed a structure in which the densely packed Au NPs monolayer and the resin bead are the shell and the core, respectively. Each Au NPs–resin sphere could be used as a surface-enhanced Raman scattering (SERS) substrate with high SERS-enhancing capacity and reproducibility. The SERS enhancement factor (EF) was estimated at 109–1011 by using thiophenol as the probe. The spatial and sphere-to-sphere variations in SERS EF were <18%. The SERS-enhancing capacity could be tuned by varying the Au NPs size. The detection limit of paraquat in water by SERS using the as-synthesized Au NPs–resin as active substrate was ∼10−12 M. The fabrication method could be a promising alternative to the preparation of well-ordered NPs arrays for SERS-active substrates.