Controlling the Dynamic Instability of Capped Metal Nanoparticles on Metallic Surfaces

Scanning Tunneling Microscopy Study of Lipoic Acid, Mannose, and cRGD@AuNPs Conjugates

The functionalization of AuNPs with different biological elements was achieved to investigate their possibility in biomedical applications such as drug delivery, vaccine development, sensing, and imaging. Biofunctionalized AuNPs are pursued for applications such as drug delivery, vaccine development, sensing, and imaging. In this study, AuNPs with diameters of 20 nm were functionalized with lipoic acid, mannose, or the cRGD peptide. By using UV-vis spectroscopy, Fourier transform infrared spectroscopy, dynamic light scattering, transmission electron microscopy, and scanning tunneling microscopy techniques, we showed that AuNPs can be functionalized by these biomolecules in a reliable way to obtain conjugates to explore potential biomedical applications. In particular, we demonstrate that the STM technique can be employed to analyze biofunctionalized AuNPs, and the obtained information can be valuable in the design of biomedical applications.

Effect of Ligands on the Stability of Gold Nanoclusters

Gold nanoclusters (AuNCs) are atomic architectures that can be precisely tailored for catalytic applications. In this work, we studied two benchmark AuNCs, Au₂₅(SR)₁₈ and Au₁₄₄(SR)₆₀, covered by aromatic and aliphatic ligands to envision how the 3D structure of the ligand impacts the stability of the nanomaterial. Surprisingly, we found that increasing the alkanethiol length has a poor or null effect on the stability of the AuNCs, a trend opposite to that on Au(111) surfaces. When considering the aromatic or aliphatic nature, the AuNC stability follows the same trend as on Au(111): the thermodynamical stability is dictated by the ligand density rather than its chemical nature, where the aliphatic ligand imparts more stability than the aromatic one. Our findings provide a tool to predict how an ultrasmall gold core can interact with the environment, substrate, and themselves according to the stability of its protecting ligand shell.

Nanostructured surfaces from ligand-protected metal nanoparticles

Nanostructuring surfaces with metal atoms or clusters represents a promising approach to create materials with unique electronic/magnetic properties and improved chemical reactivity. By means of plasma sputtering and mass spectrometric techniques, the deposition of precisely size-selected clusters onto single-crystal surfaces has been applied to prepare surfaces with tailored properties. However, nanostructured surfaces can as well be prepared with metal nanoparticles via solution-phase methods, but the difference is that nanoparticles prepared by wet chemistry are usually coated with a layer of ligands, which are essential not only for maintaining the size and the atomic structure of metallic cores, but also for playing crucial roles in the synthesis, physicochemical properties and catalytic activities of the nanoparticles. This Frontier covers aspects of nanostructured surfaces from ligand-protected metal nanoparticles, starting with high-resolution imaging of the ligand-protected metal nanoparticles, followed by periodic patterning of metal nanoparticles on surfaces and the well-controlled atomic layer deposition with nanoclusters at the liquid/solid interface. We also highlight the potential of the surface-supported structures from ligand-protected metal nanoparticles, and the challenges remaining to be tackled.

Doping of thiolate protected gold clusters through reaction with metal surfaces

A new technique is introduced for doping gold nanoclusters by using a metal surface such as Ag, Cu and Cd as a source of heteroatoms. The importance of the thiol ligand in the doping process is examined by following the reactions with MALDI-TOF mass spectrometry in the presence and the absence of the thiols on the surface. The doping reactions depend greatly on the type of the cluster and the availability of the ligand which is a crucial element for alloying. The thiol acts as a messenger exchanging the metal atoms between the cluster and the metal surface as revealed by the XPS studies performed on the metal surfaces.

Resonance Raman study of the J-type aggregation process of a water soluble perylene bisimide

Resonance Raman spectroscopy offers a detailed molecular picture of the conformation of a water-soluble PBI in a supramolecular J aggregate.

Variable Growth and Characterizations of Monolayer-Protected Gold Nanoparticles Based on Molar Ratio of Gold and Capping Ligands

Controlling the size of nanoscale entities is important because many properties of nanomaterials are directly related to the size of the particles. Gold nanoparticles represent classic materials and are of particular interest due to their potential application in a variety of fields. In this study, hexanethiol-capped gold nanoparticles are synthesized via the Brust-Schiffrin method. Synthesized nanoparticles were characterized by various analytical techniques such as transmission electron microscopy, scanning tunneling microscopy (STM), UV-visible absorption spectroscopy and electrochemical techniques. We have varied the molar ratio of gold to the protecting agent (hexanethiol) to discover the effect of gold-to-hexanethiol ligand ratio on the size of gold particles. The clear correlation between particle size and molar ratio is found that the averaged particle size decreases from 4.28 ± 0.83 to 1.54 ± 0.67 nm as the gold-to-ligand molar ratio changes from 1:1 to 1:9. In contrast to a recent report that thiolated gold nanoparticles are under spontaneous disintegration when they are assembled on a gold substrate, our STM experiments proved that these gold nanoparticles can form a stable monolayer or multiple layers on the platinum electrode without observing disintegration within 72 h. Therefore, our STM experiments demonstrate that the disintegration behavior of gold nanoparticles is related to the type of ligands and the nature of substrate materials. In electrochemical experiments, these gold nanoparticles displayed an electrochemical quantized charging effect, making these nanoparticles useful in the device applications such as electrochemical or biological sensors.