Preparation of Monolayer Photonic Crystals from Ag Nanobulge-Deposited SiO2 Particles as Substrates for Reproducible SERS Assay of Trace Thiol Pesticide

Abstract

Surface-enhanced Raman scattering (SERS) greatly increases the detection sensitivity of Raman scattering. However, its real applications are often degraded due to the unrepeatable preparation of SERS substrates. Herein presented is a very facile and cost-effective method to reproducibly produce a novel type of SERS substrate, a monolayer photonic crystal (PC). With a building block of laboratory-prepared monodisperse SiO2 particles deposited with space-tunable silver nanobulges (SiO2@nAg), a PC substrate was first assembled at the air–water interface through needle tip flowing, then transferred onto a silicon slide by a pulling technique. The transferred monolayer PCs were characterized by SEM and AFM to have a hexagonal close-packed lattice. They could increase Raman scattering intensity by up to 2.2 × 107-fold, as tested with p-aminothiophenol. The relative standard deviations were all below 5% among different substrates or among different locations on the same substrate. The excellent reproducibility was ascribed to the highly ordered structure of PCs, while the very high sensitivity was attributed to the strong hotspot effect caused by the appropriately high density of nanobulges deposited on SiO2 particles and by a closed lattice. The PC substrates were validated to be applicable to the SERS assay of trace thiol pesticides. Thiram pesticide is an example determined in apple juice samples at a concentration 102-fold lower than the food safety standard of China. This method is extendable to the analysis of other Raman-active thiol chemicals in different samples, and the substrate preparation approach can be modified for the fabrication of more PC substrates from other metallic nanobulge-deposited particles rather than silica only.

Iridescent Colloidal Crystals Composed of SiO2 Porous Hollow Sphere for SERS Application

“…Here, SPHS CC structures could have three key advantages as SERS substrates. First, the pores between spheres have low surface energy and can easily be filled by gold or silver nanoparticles, thereby increasing the number of hot spots. , Second, the curvature of the spherical particles can increase the distance between metal nanoparticles during the loading process, thereby avoiding the production of resonance through close proximity. − Third, the laser beam reflected by the PBG increases the signal feedback received by the detector, and thus a high Raman spectral resolution can be obtained. − The SEM image (Figure S4) shows that the sample has a periodically arrangement on the surface and in the cross section. The energy-dispersive X-ray spectroscopy (EDS) mapping of the sample surface can be analyzed for the presence of a uniform distribution of Au.…”

“…Photonic crystals (PCs) are arrays of two materials with different refractive indices. − Well-dispersed colloidal particles that self-assemble into colloidal crystals (CCs) have attracted great interest as a simple and low-cost alternative to PCs. − The optical properties of CCs with photonic band gaps (PBGs) can limit the transmission of electromagnetic waves of specific wavelengths. − Structural colors can be observed with the naked eye when the PBG falls within the range of visible light. , PBGs play crucial roles in optical waveguide materials. When the PBG wavelength overlaps with that of the laser Raman spectrum, a high-intensity Raman spectrum can be obtained. − Moreover, CC arrays have a larger effective surface area compared with flat substrates, thus exposing more hot spots. − Therefore, CCs with high surface area should be suitable for application as SERS substrates.…”

Advances in functional photonic crystal materials for the analysis of chemical hazards in food

“…The Raman detection of mycotoxin based on silica inverse opal photonic crystal microsphere (SIPCM) (a) (Jiao et al, 2022). Preparation and application of Single layer photonic crystal surface-enhanced Raman scattering (PC SERS) substrate (b) (C. Zhang, Xu, et al, 2020) SiO 2 @Ag nanoparticles to assemble monolayer PC, and used the hot spot of the substrate to detect thiram pesticide, the detection limit was as low as 34.7 μg/L (Figure 6b). The substrates prepared in this way can detect thiol substances by the SERS method.…”

“…Label‐free fluorescence turn‐on detection could also be achieved based on the interaction between the fluorescent dye and the mycotoxin‐induced G‐quadruplex structured aptamer (Figure 5a) (D. Zhang, Cai, et al., 2020). The well‐designed aptamer could form a G‐quadruplex in the presence of its target mycotoxin.…”

“…The Raman detection of mycotoxin based on silica inverse opal photonic crystal microsphere (SIPCM) (a) (Jiao et al., 2022). Preparation and application of Single layer photonic crystal surface‐enhanced Raman scattering (PC SERS) substrate (b) (C. Zhang, Xu, et al., 2020)…”