Influence of Gold Nanoparticle Assembly in Langmuir–Schaefer Monolayers on the Surface-Enhanced Spectroscopy Response of a Nanoplatform

Abstract

Gold nanoparticles (Au-NPs) are among the most commonly used materials for increasing the sensitivity of Raman spectroscopy. This is mainly due to the strong and tunable surface plasmon resonances, which can be easily adjusted by choosing the shape and size of individual NPs. However, recent findings indicate that controlling the density of NPs in their assemblies is an equally important parameter. An efficient way to achieve such control is by using the Langmuir–Schaefer technique, which yields single-layer assemblies of NPs on a solid substrate. In this study, we correlate the density and thermodynamic properties of a monolayer of spherical Au-NPs with their performance as Raman substrates. Hence, hydrophobic NPs were synthesized and assembled into films using the Langmuir–Schaefer technique. The surface-enhanced Raman spectroscopy (SERS) showed various degrees of enhancement depending on the different ranges of transfer surface pressures employed, which almost doubled the expected SERS signal intensity at the highest deposition surface pressure. To gain greater insights into this phenomenon, we investigated the NP distribution in the Langmuir and Langmuir–Schaefer films by detailed spectroscopic and electron and optical microscopic analyses. A correlation was observed between NP enhancements on the micro- and nanoscale. The presented results demonstrated the potential of adjusting the Raman responses in ultrasensitive detection by controlling the thermodynamic properties of NP monolayers.

The Role of the Polyethylene Glycol in the Organization of Gold Nanorods at the Air–Water and Air–Solid Interfaces

“…According to our previous studies for gold nanorods, the formation of aggregates at the microscale is influenced by the dewetting process that takes place during substrates pulling from the air–water interface, while at the nanoscale, Au-NRs tend to form two main aggregate structures. Similar results for spherical shape NPs showed different arrangements of NPs at the micro- and nanoscale . One is end-to-end , and the second is side-to-side .…”

“…Similar results for spherical shape NPs showed different arrangements of NPs at the micro- and nanoscale. 34 One is end-to-end , and the second is side-to-side . 35 The two types of structures dominate the shape of the spectra shown in Figure 3 and thus produce strong plasmon coupling.…”

Starch Sodium Octenylsuccinate as a New Type of Stabilizer in the Synthesis of Catalytically Active Gold Nanostructures

“…Among the metallic NPs, AuNPs are distinguished by their unique catalytic properties [1][2][3]. In addition, the phenomenon of localized surface plasmon resonance occurring in NPs allows for the utilization of AuNP assemblies as enhancers in surfaceenhanced Raman spectroscopy (SERS) and as photothermal agents [4][5][6][7].…”