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The nanoparticle density (PD) of the substrates is crucial for surface‐enhanced Raman scattering (SERS) performance. Here, bottom‐up SERS substrates based on rough gold nanorods (R‐Au NRs) with different PD are fabricated and their SERS property are investigated. In particular, R‐Au NRs are deposited on the Si wafer from sparse to dense through electrostatic interaction and from monolayer to multiple layers by interface self‐assembly technique. It is found that the SERS intensity increases dramatically with increasing PD and remains almost unchanged when the PD increases to 241.22 counts µm−2, and the limited penetration depth of laser is the reason for the intensity saturation. Additionally, similar results are observed in the smooth Au NRs substrates, re‐confirming the PD‐dependent SERS performance. Importantly, the SERS activity of R‐Au NRs substrates is higher than smooth Au NRs substrates in each PD, indicating that R‐Au NRs can produce stronger electromagnetic field enhancement, which is supported by the theoretical simulation results. Finally, it is demonstrated that the optimal SERS substrates can be effectively utilized for the quantitative measurement of thiram in soil. Briefly, the PD of substrates has a great impact on SERS activity, which offers an idea for the design of highly efficient SERS substrates. [ABSTRACT FROM AUTHOR]

[Display omitted] Broadband surface-enhanced Raman scattering (SERS) substrates can achieve strong SERS enhancement at multiple excitation wavelengths, which is highly desirable in diverse fields. Here, a facile and reliable interfacial layer-by-layer self-assembly technique was proposed to construct broadband and sensitive Au@Ag nanorod (NR) monolayer film over nanosphere (MFON) substrate. The Au@Ag NR MFON substrate with ultra-broad spectrum from visible to near-infrared region was achieved by varying the shape of plasmonic nanoparticles, which exhibits excellent SERS activity at different excitation wavelengths. Besides, the size of Au@Ag NRs and polystyrene spheres, and the layer numbers of Au@Ag NR film were altered to optimize the sensitivity of SERS substrates. Notably, the SERS intensity of the optimally designed Au@Ag NR MFON substrate is 25-fold larger than that of Au@Ag NR monolayer film deposition on the plane Si wafer. Furthermore, the optimal Au@Ag NR MFON substrate presents excellent reproducibility and a much wider quantitative detection range, which enables a wide-linear-range analysis of thiram in grape juice by a portable Raman spectrometer. Therefore, we envision that this study opens a new avenue toward the design of ultra-sensitive and broadband SERS platforms with widespread applications. [ABSTRACT FROM AUTHOR]

The concave star-shaped Au nanocrystals with ten sharp tips endowed them with 12-fold higher SERS enhancements than Au nanospheres. • Au nanocrystals with sharp tips were prepared using pentatwinned Au NSs as seed. • Au nanocrystals provided a broad spectral range from VIS to NI region. • Monolayers of Au nanocrystals displayed strong shape-dependent SERS activity. • Concave nanostars was 12-fold higher SERS enhancement than Au NSs. In this work, various geometries of Au nanocrystals with sharp tips including decahedra, concave star, and spindle were synthesized through Ag underpotential deposition-dominated growth approach based on utilizing a novel type of Au nanoseed (i.e., pentatwinned Au nanospheres). These as-prepared Au nanocrystals exhibited a broad localized surface plasmon resonance (LSPR) tunability from visible to near-infrared region. Furthermore, we fabricated the monolayer film based on Au nanocrystals with different morphologies through liquid/liquid interface self-assembly technique, which displayed strong shape-dependent surface enhanced Raman scatting (SERS) performance. More significantly, concave star-shaped Au nanocrystals with ten sharp tips endowed them with 12-fold higher SERS enhancements than Au nanospheres, which was in line with the simulation results by finite difference time domain (FDTD) method. Our study provides a novel route for fabrication of Au nanocrystals with diversified structures, and the efficient SERS substrates have great prospect for the applications in ultrasensitive chemical and biological sensing. [ABSTRACT FROM AUTHOR]