Fabrication of macroscopic polydimethylsiloxane cavity arrays decorated with Ag nanoparticle dimers as SERS substrates for rapid pesticide detection.

A practical surface-enhanced Raman scattering (SERS) substrate is reported constructed by depositing Ag nanoparticle dimers (Ag NDs) onto a polydimethylsiloxane (PDMS) film with macroscopic cavity arrays (MCA). This design integrates the synergistic advantages of large-aperture and shallow-depth MCA, as well as Ag NDs with abundant nanogaps, achieving a well-balanced combination of sensitivity, uniformity, and operability for rapid testing. The open MCA structure, fabricated using commercial toothbrush bristles as a template, not only facilitates analyte enrichment through spatial confinement but also serves as a patterned scaffold for depositing densely plasmonic Ag dimer arrays, which generates high-density SERS hotspots. The optimized Ag NDs@MCA substrate exhibits desirable SERS performance, including good sensitivity, satisfactory uniformity, and reliable batch-to-batch reproducibility. Furthermore, the naked-eye-distinguishable cavities allow direct visual positioning of detection sites, significantly simplifying testing operation. Coupled with a portable Raman spectrometer, the as-prepared SERS substrate achieved fast trace determination of malachite green (10⁻6 M) in lake water and thiram (10⁻7 M) on apple surfaces. This low-cost, practical SERS substrate demonstrates great potential for on-site environmental monitoring and food safety screening.