Self-assembly of metal nanoparticles has attracted considerable attention because of its unique applications in technologies such as plasmonics, surface-enhanced optics, sensors, and catalysts. However, fabrication of ordered nanoparticle structures remains a significant challenge. Thus, developing an efficient approach for the assembly of large-scale Au nanoparticles films for theoretical studies and for various applications is highly desired. In this paper, a facial approach for fabricating a monolayer film of Au nanoparticles was developed successfully. Using the surfactant polyvinylpyrrolidone (PVP), a large-scale monolayer film of well-ordered, uniform-sized Au nanoparticles was fabricated at the air/water interface. The film exhibited a two-dimensional (2D) hexagonal close-packed (HCP) structure having interparticle gaps smaller than 2 nm. These gaps generated numerous uniform "hot spots" for surface-enhanced Raman scattering (SERS) activity. The as-prepared monolayer film could be transferred to a solid substrate for use as a suitable SERS substrate with high activity, high uniformity, and high stability. The low spot-to-spot and substrate-to-substrate variations of intensity (<10%), the large surface enhancement factor (∼10(6)), and the high stability (∼45 days) make the substrate suitable for SERS measurements. Transfer of the monolayer film onto a glassy carbon electrode produced an Au electrode with clean, well-defined nanostructure suitable for electrochemical SERS measurements. The adsorption process of ionic liquids on the electrode with the monolayer film is similar to that on bulk metal electrodes. The present strategy provides an effective way for self-assembly of Au nanoparticles into well-defined nanostructures that may form optimal reproducible SERS substrates for quantitative analysis. It also provides an electrode with clean, well-defined nanostructure for electrochemical investigations.

Surface plasmon plays an important role in surface catalysis reactions, and thus the tuning of plasmon on metal nanostructures and the extension of plasmon induced surface catalysis reactions have become important issues.

Two kinds of room-temperature ionic liquids, 1-butyl-3-methylimidazolium bromide ([BMIM]Br) and 1-butyl-3-methylimidazolium tetrafluoroboride ([BMIM]BF4 ), were used as solvent, and the adsorption of the ionic liquids themselves and of N-methylimidazole (NMIM) were investigated by electrochemical surface-enhanced Raman scattering (SERS) over a wide potential window. The results revealed that the cation of ionic liquid adsorbed onto Cu surface with different configurations in different potential ranges. When the potential was changed from the negative to the positive range, the orientation underwent a change from flat to vertical, and the onset potential for the orientation change was dependent on the types of anion of the ionic liquid. The ionic liquid in bulk solution exhibited a remarkable effect on the adsorption of NMIM. The electrode surface structure changed from adsorbing the ionic liquid at the negative potential to coadsorbing the ionic liquid and NMIM at relative positive potential for the [BMIM]BF 4 liquids, and formed films of NMIM at extremely positive potential. Due to the strong specific adsorption of Br − , the coadsorption of ionic liquid and NMIM was not observed in the system [BMIM]Br. By simulating the electrode surroundings, two surface complexes [Cu(NMIM) 4 Br]Br·H 2 O and [Cu(NMIM) 4 ](BF 4 ) 2 were synthesized by the electrochemical method in the corresponding ionic liquids for modeling the surface coordination chemistry of NMIM. The surface coordination configuration of NMIM and ionic liquids is proposed.

In this paper, we reported a facile strategy to fabricate a PDMS film-coated Au nanoparticle monolayer film (Au MLF) composite substrate for improving SERS detection of aromatic molecules in water and in the atmosphere.

A novel and highly sensitive immunoassay method based on surface enhanced Raman spectroscopy (SERS) and magnetic particles has been developed. This method exhibits great potential application in bio-separation and immunoassay.