Interfacial layer-by-layer self-assembly of PS nanospheres and Au@Ag nanorods for fabrication of broadband and sensitive SERS substrates.

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.