Abstract
In this study, hexagonal-packed Si nanorods (SiNRs) arrays were fabricated and conjugated with Au nanoparticles (AuNPs) in different spatial distributions for surface-enhanced Raman spectroscopy (SERS). The AuNPs were functionalized on the bottom of SiNRs (B-SiNRs@AuNPs), top of SiNRs (T-SiNRs@AuNPs) and sides of SiNRs (S-SiNRs@AuNPs), respectively. Our results demonstrated that the SiNRs conjugated with AuNPs on the sides achieved high reproducibility in detection of R6G molecules, while the AuNPs on the top of the SiNRs obtained the strongest Raman enhancement. In addition, the substrate with S-SiNRs@AuNPs obtained the highest spatial uniformity of enhancement. The finite-difference time-domain simulation gave further evidence that the incident light could be confined in the space of SiNRs arrays and yield a zero-gap enhancement coupled with the AuNPs. Our study provided a spatially tunable SiNRs@AuNPs substrate with high sensitivity and reproducibility in molecular detection.
Highlights
Surface-enhanced Raman spectroscopy (SERS) has developed quickly since its discovery into a powerful molecular analytical tool [1,2,3]
The scanning electron microscopy (SEM) images clearly reveal the successful functionalization of Au nanoparticles (AuNPs) on the top, side and bottom of the Si nanorods (SiNRs)
The S-SiNRs@AuNP substrate achieved high reproducibility and spatial uniformity (RSD as low as 6.3%). This is mainly contributed by the coupling of the sphere AuNPs, inducing a strong localized surface plasmon resonance (LSPR) around the SiNRs, as well as the wide range of antinodes connected in the electric field between SiNRs
Summary
Surface-enhanced Raman spectroscopy (SERS) has developed quickly since its discovery into a powerful molecular analytical tool [1,2,3]. Electron-beam/laser lithography could be more precise and editable with respect to fabrication, but the results would be limited in size and more expensive Overall, those creatively fabricated SERS substrates incorporate a designed ordered narrow gap in the metal nano/microstructures and achieve high sensitivity and reproducibility. Repeated and multiple light scattering in photonic microarrays can enhance the matter–light interaction In another case, the self-assembly of AuNPs on a 3D nanocup array structure generated strong LSPR effects due to additive optical coupling between two plasmons [30]. The self-assembly of AuNPs on a 3D nanocup array structure generated strong LSPR effects due to additive optical coupling between two plasmons [30] Those multiple coupling approaches were able to produce enhancements on the order of 107~109 over a wide area. To achieve the large-area ordered hexagonal-packed SiNRs substrate, sphere lithography and metal assisted chemical etching methods were used. We provided different AuNPs and SiNRs conjugation modes, which could be selectively used in SERS detection
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