Quantitative Surface-Enhanced Raman Spectroscopy through the Interface-Assisted Self-Assembly of Three-Dimensional Silver Nanorod Substrates.

The realization of surface-enhanced Raman spectroscopy (SERS) to be a reliable quantitative analytical technique requires sensitive and reproducible enhancing substrates. Here, uniform three-dimensional (3D) Ag nanorod (AgNR) substrates with well-defined interlayer spacings are prepared through the air-liquid interface-assisted self-assembly of AgNR in a layer-by-layer manner. The correlation of the SERS performance with the 3D AgNR structures is performed by SERS mapping the substrates. SERS mapping reveals the excellent enhancement uniformity of the 3D substrates with the relative standard deviation (RSD) less than 10%. It finds that both of the number of layers (NL) and the length of the AgNR have effects on the SERS performance of the 3D AgNR substrates. It is demonstrated that the intergaps between layers contribute much to the SERS intensity of the 3D AgNR by creating the interlayer (out-of-plane) plasmonic coupling. The impact of the excitation wavelengths (532, 633, and 785 nm) on SERS performance is also determined. The optimal 3D AgNR structures achieved by the correlation study is further used to detect a set of related molecules (l-tryptophan (Trp), l-phenylalanine (Phe), urea, and melamine). The 3D AgNR SERS of the analytes exhibits linear responses over wide concentration ranges. The sensitivity of the 3D AgNR SERS is proved by comparing to that of the current methods. Moreover, the 3D AgNR substrates maintain the performance stability during 4 weeks of storage.