Self-Assembled Large-Scale Monolayer of Au Nanoparticles at the Air/Water Interface Used as a SERS Substrate

Abstract

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.

Advances in surface-enhanced vibrational spectroscopy at electrochemical interfaces

“…The nanoparticle ensemble approach to EC-SERS has been applied to various systems in recent years including ionic liquid adsorption [40,41], pyridine adsorption [42], uric acid detection [43] and DNA hybridisation [44]. The dye compound Nile Blue (NB) has found significant attention as a probe molecule in this arena due to its strong resonance Raman signal which is lost upon its two-electron reduction [45][46][47][48][49][50].…”

Light welding nanoparticles: from metal colloids to free-standing conductive metallic nanoparticle film

“…For example, electric circuits can be printed using metallic nanoparticles (NPs) as "electric ink" [6,7]. Self-assembly of NPs at a fluid interface is another attractive method [1, [8][9][10][11][12]. Because interfacial self-assembly of NPs usually produces a two-dimensional (2D) monolayer film, metallic thin films with well controlled thickness can be easily fabricated by choosing NPs with a desired diameter and by repeating the monolayers of the 2D film transferred onto the host substrate.…”

Air‐Liquid Interfacial Self‐Assembly of Two‐Dimensional Periodic Nanostructured Arrays

“…Liu and co‐workers reported the vertical segregation in the one‐step self‐assembly of AuNPs with bimodal size distribution at the air‐liquid interface . Guo and coworkers reported a simple self‐assembly approach to fabricate 2D PVP‐coated AuNPs array with an hcp ordering at the air‐water interface (Figure E) and successfully applied such Au hcp arrays as the surface‐enhanced Raman scattering (SERS) substrates …”