Langmuir and Langmuir–Blodgett Films of Gold and Silver Nanoparticles

Abstract

Recently the focus of the Langmuir–Blodgett technique as a method of choice to transfer monolayers from the air/water interface onto solid substrates in a controllable fashion has been shifting toward purely hydrophobic gold and silver nanoparticles. The fundamental interactions between particles that become relevant in the absence of polar groups range from dispersive attractions from the metal cores and repulsions between ligand shells to weaker entropic factors. The layer evolution is explored, starting with interfacial self-assembly upon solution spreading and domain and circular island formation, which subsequently merge into a complete monolayer and finally form multilayers or macroscopic wrinkles. Moreover, structural properties such as the core:ligand size ratio are investigated in the context of dispersive forces, whereby the nanoparticles with small cores and long ligands tend not to aggregate sufficiently to produce continuous films, those with large cores and short ligands were found to aggregate irreversibly, and those in between the two extremes were concluded to be able to form highly organized crystalline films. Similarly, the characteristics of the spreading solution such as the concentration and the solvent type crucially influence the film crystallinity, with the deciding factor being the degree of affinity between the capping ligand and the solvent used for spreading. Finally, the most common strategies employed to enhance the mechanical stability of the metal nanoparticle films along with the recent attempts to functionalize the particles in attempts to improve their applicability in the industry are summarized and evaluated in relation to their future prospects. One of the objectives of this feature article is to elucidate the differences between hydrophobic metal nanoparticles and typical amphiphilic molecules that the majority of the literature in the field describes and to familiarize the reader with the knowledge required to design Langmuir–Blodgett nanoparticle systems as well as the strategies to improve existing ones.

Recent Advances in Conjugated Polymer-Based Biosensors for Virus Detection

“…In this study, PDA nanovesicles were first prepared by functionalizing PDA with M149 antibody, and immobilization of these PDA nanovesicles on PVDF membrane showed a further improved stability and sample handling. However, currently conventional approaches for fabrication of solid-phase CP colorimetric biosensors have often relied on Langmuir–Blodgett (LB) or Langmuir–Schaeffer (LS) films [ 98 ]. These methods presented weak optical signals and required stringent conditions.…”

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

“…One approach used to resolve the aforementioned problem is the use of the Langmuir technique. This technique is widely known as the typical method for the fabrication of 2D assemblies to study the structures and properties of substances such as lipids, proteins, and NPs. − However, the known concepts of Langmuir layer formation confirmed that layers consisting of metallic NPs show different types of interactions compared to those consisting of amphiphilic molecules. In the context of NPs, it requires the dispersion of NPs at the air–water interface, while the desired packing density, distribution, and interactions of NPs are controlled via surface pressure (π), which can be adjusted by pushing the Langmuir barriers toward each other.…”

Electric Field-Driven Self-Assembly of Gold Nanoparticle Monolayers on Silicon Substrates

“…Various methods have been developed for the 2D self-assembly of NPs on a substrate surface, including Langmuir–Blodgett (L–B) deposition technique, which is commonly employed for two-dimensional (2D) self-assembly of hydrophobic organic ligand-coated NPs into a close-packed monolayer film at the air–water interface . Then, monolayers are transferred to the solid substrates using the classical Langmuir–Schaefer (L–S) method, where a hydrophobic surface, such as a carbon-coated transmission electron microscopy (TEM) grid, is horizontally touched to the monolayer of NPs to lift it. , However, this method is limited to hydrophobic surfaces, and a large area of the monolayer is often challenging to obtain.…”

“…The surfactant coating on these NPs creates a repulsion barrier that prevents their cores from agglomerating irreversibly. In the solution, there are two fundamental interactions between the particles: core–core attractions and ligand–ligand repulsions . This allows the NPs to modify their relative positions until they form a low-energy, self-organized pattern, such as 2D monolayers. , It is also investigated in one of the experiments using SNIFTIR spectra of Cit-Au-NPs (111) that, via COOH hydrogen bonds, the adsorbed citrate on the Au-NPs surface interacts with a different kind of citrate anion in the solution .…”