We here present electronic structures and chiroptical responses of gold-based bimetallic nanoclusters protected by chiral thiolate ligand, glutathione (GSH), and compare them with those of monometallic counterparts. The nanoclusters examined are AuPd and AuAg bimetallic systems. The effect of Pd or Ag doping on the chiroptical responses of optically active Au nanoclusters as well as the importance of the bimetallic core configurations are discussed. Briefly, we find that GS-protected AuPd or AuAg nanoclusters exhibit quite different Cotton effects from those of the monometallic nanoclusters in metal-based electronic transition regions. In the AuPd system, all bimetallic nanoclusters exhibit featureless absorption profiles, but their circular dichroism (CD) signals are structured, offering a greater advantage in detecting a foreign atom doping in the nanocluster system. In the AuAg system, the nanocluster compounds exhibit relatively weaker CD responses than those of the corresponding Au compounds. This CD decrease can be explained in terms of the increased geometrical isomers that are formed by statistical distribution of Ag heteroatoms in the nanocluster, since an increased number of possible configurations gives an average in the CD response with positive and negative bands of different optical isomers.

Bimetallic nanoparticles (NPs), particularly Au/Pd and Au/Pt, have attracted extensive attention due to their wide-spread application in catalysis, optoelectronics and energy recuperation.[1] Here we have attempted the fabrication of Au/Pt and Au/Pd bimetallic NPs by an energy-efficient eco-friendly microwave methodology. The microwave-assisted reactions enable considerably large product yields over conventional colloidal methods due to (a) almost two-fold increased reaction kinetics, (b) localized superheating at reaction sites and rapid rise of initial temperature.[2] Au NPs (sizes 20 ± 3 nm) are fabricated in the first step followed by the reduction of [PdCl2(NH3)2] or [K2PtCl6]in tetraethylene glycol at 180 ºC for 2 min. Controlling and understanding the atomic structure and elemental distributions of these NPs are crucial for their optimized performances. So, we address the fundamental question of the most likely arrangement of Au and Pd or Pt atoms in these bimetallic NPs prepared under similar conditions by complementary characterizations using UV-Vis spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The UV-Vis spectroscopy reveals the formation of an alloy shell. The extent of depression of the plasmon peak of Au and its blue-shift reveals substantial deposition of Pd atoms on an Au core and significant alloying in comparison to Au/Pt NPs. XRD reveals the gradual shift of the diffraction peak from the position of Au to the position of Pd or Pt with change in composition. XRD supports the formation of a thick alloy shell in these NPs. However, the TEM images reveal a very interesting result. With increase in Pt concentration, the size of the dispersed NPs decreases from 20 ± 3 nm to about 16 nm (± 1 nm) and there is evolution of a bimodal particle size distribution with small particles about 1-2 nm diameters. On the contrary, with increasing Pd concentration, the particle size of the dispersed particles increases to about 32 nm (± 1 nm). This discrepancy of particle size evolution for the two systems arises due to the differences in surface energies (Pt > Pd > Au atoms). Pt atoms tend to diffuse towards the core with the formation of Au nano-islands which eventually segregates leading to a reduction in particle size and bimodal distribution. At higher concentration of Pt, Pt and Au atoms tend to nucleate separately also contribute to the bimodal distribution. While for Au/Pd NPs, we have an Au core with an alloyed shell having higher Pd concentration. This is further supported by experimental evidence by selective etching and dissolution of Au by potassium-iodide solution. Furthermore, the Au/Pd bimetallic NPs are found to possess better catalytic activities in the reduction of 4-nitrophenol to 4-aminophenol than Au/Pt and monometallic NPs.

Ag or Au nanocubes are known to be plasmonic nanoparticles with strong plasmonic fields concentrated around their corners1. When these nanoparticles aggregate the individual plasmonic oscillations of each particle begin to couple. The coupling between the two plasmonic nanoparticles is assumed to be dipolar in nature which results in an exponential red shift dependence of their localized surface plasmon resonance (LSPR) on the dimer separation2. Unfortunately, this exponential behavior is shown to fail as the separation distance between the two 42 nm nanocube dimer becomes 6nm or smaller3. Hooshmand et al4 have noted that these separation distances are marked by the formation of hot spots between the facets of the dimer.

This dipolar exponential behavior results from a treatment of the coupling between the two excited nanocubes as a coupling between two oscillating dipole moments2. As a result, the vectorial addition of all the oscillating electronic dipoles is assumed to interact with the nearest nanoparticle as a single oscillating electronic dipole. Herein we suggest that as the separation distance becomes increasingly small, the coupling between the individual oscillating dipoles on the different nanocubes becomes significant. Thus, the dipolar exponential behavior fails to accurately predict the near field coupling between two nanoparticles with small separation distances.

This leads to the realization that the interaction between the individual oscillating dipoles on the two nanocubes changes in a complicated manner as a function of separation distance. At 2nm, a good fraction of the oscillating dipoles are between the adjacent facets of the nanocubes as well as between the the corners. While at 3 nm less are in between the two facets of the nanocubes and a larger portion are localized at the corners. Thus, the coupling is not only dependent on the separation distance but also on what the separation does to the net interaction between the oscillating dipoles on each facet of the two coupled nanocubes. This results in the failure of the exponential behavior as the dipole moment on each nanocube is changing with distance in a complicated manner.

We propose a theoretical designed peptide-Au cluster probe and realize spatially marking and quantitatively counting αIIbβ3 integrin via this novel nanoprobe. On single cell level, we find the number of αIIbβ3 integrin ranges from 5.75 to 9.11×10-17 mol for the heteroexpression of individual cells. Because the variation of proteins (including integrin and other biomarkers) on single cell has a tight correlation with many serious human diseases, our quantifying protein method on a single cell level is helpful for estimating the disease progression for diagnosis and detecting the drug response for therapy.

Gold nanoclusters with precisely controlled atomic composition have emerged as promising materials for applications in nanotechnology because of their unique optical, electronic and catalytic properties. The recent discovery of a 20-gold-atom nanocluster protected by 16 organothiolate molecules, Au20(SR)16, is the smallest member in a surprising series of small gold−thiolate nanoclusters with a face-centered cubic (FCC) ordered core structures. A fundamental challenge facing gold nanocluster research is being able to understand the composition-dependent properties from a site-specific perspective in order to confidently establish structure-property relationships. A step in this direction is to examine the influence of various structural features (core geometry and thiolate-gold bonding motifs) on the bonding properties of gold-thiolate nanoclusters. In this work, ab initio simulations were conducted to systematically study the local structure and electronic properties of Au20(SR)16 from each unique Au and S atomic site using Au L3-edge extended X-ray absorption fine structure (EXAFS), projected density of states (l-DOS) and S K-edge X-ray absorption near edge structure (XANES) spectra. Two larger FCC-like gold-thiolate nanoclusters (Au28(SR)20 and Au36(SR)24) were used for a comparative study with Au20(SR)16, providing further predictions about the cluster size effect on the bonding properties of gold-thiolate nanoclusters with FCC-like core structures. Through this comparison, the smaller core size of Au20(SR)16 produces an EXAFS scattering signature that is non-FCC-like but shows very similar electronic properties with a larger FCC-like gold-thiolate nanocluster.

We present gold (Au) and silver (Ag) nanoparticles (NPs) could be used not only for stimuli-responsive optical sensors but also for the quantification of radical compounds when these nanoparticles are suitably combined with polymeric materials. When Au NPs are assembled 2-dimensionally on the surface of hydrogel NPs which respond to temperatures, the hybrid NPs displayed thermoreversible multiple color switching. Accordingly, optical bandwidths of the hybrid NPs are reversibly changed with temperatures: with hybrid NPs assembled with 51 nm Au NPs, prominent optical signals are recorded at 900 nm at 50 °C while most of extinction signals are shown below 600 nm at room temperatures. In addition, we demonstrate the modification of Ag NPs’ surfaces (nanocubes and nanospheres) with polyelectrolytes (either positive or negative) could extend the quantifiable detection ranges of radical compounds. Through the surface modification of Ag NPs, the polyelectrolytes protect the Ag NPs by probably either retarding (forming diffusion barriers) or preventing (blocking/entrapping/scavenging) the arrival of radicals to Ag NPs or both. The roles of the polyelectrolytes are demonstrated by using radical compounds produced from tetrahydrofuran and H2O2. From the results, we could obtain calibration curves for the wide-range quantification of radical compounds.