Clusters Of Gold Atoms Research Articles

The Difference between Plasmon Excitations in Chemically Heterogeneous Gold and Silver Atomic Clusters.

Weak doping can broaden, shift, and quench plasmon peaks in nanoparticles, but the mechanistic intricacies of the diverse responses to doping remain unclear. In this study, we used the time-dependent density functional theory (TD-DFT) to compute the excitation properties of transition-metal Pd- or Pt-doped gold and silver atomic arrays and investigate the evolution characteristics and response mechanisms of their plasmon peaks. The results demonstrated that the Pd or Pt doping of the off-centered 10 × 2 atomic arrays broadened or shifted the plasmon peaks to varying degrees. In particular, for Pd-doped 10 × 2 Au atomic arrays, the broadened plasmon peak significantly blueshifted, whereas a slight red shift was observed for Pt-doped arrays. For the 10 × 2 Ag atomic arrays, Pd doping caused almost no shift in the plasmon peak, whereas Pt doping caused a substantial red shift in the broadened plasmon peak. The analysis revealed that the diversity in these doping responses was related to the energy positions of the d electrons in the gold and silver atomic clusters and the positions of the doping atomic orbitals in the energy bands. The introduction of doping atoms altered the symmetry and gap size of the occupied and unoccupied orbitals, so multiple modes of single-particle transitions were involved in the excitation. An electron transfer analysis indicated a close correlation between excitation energy and the electron transfer of doping atoms. Finally, the differences in the symmetrically centered 11 × 2 doped atomic array were discussed using electron transfer analysis to validate the reliability of this analytical method. These findings elucidate the microscopic mechanisms of the evolution of plasmon peaks in doped atomic clusters and provide new insights into the rational control and application of plasmons in low-dimensional nanostructures.

Gold nanostructures/quantum dots for the enhanced efficiency of organic solar cells.

Incorporating gold nanoparticles (AuNPs) into organic solar cell (OSC) structures provides an effective means to manipulate light-matter interactions. AuNPs have been used as plasmonic-enhancement and light-trapping materials in OSCs and exhibit diverse single and mixed morphologies. Substantial near-field enhancement from metal periodic structures has consistently demonstrated high enhancement in solar cell efficiency. Additionally, coupling with atomic gold clusters in the form of gold quantum dots holds promise for light harvesting through fluorescence phenomena. The configured devices optimize light utilization in OSCs by considering factors such as the morphology, position, and hybridization of localized surface plasmon resonance, propagating surface plasmon resonance, and fluorescence phenomena. This optimization enhances light absorption, scattering, and efficient trapping facilitated by gold nanostructures/quantum dots. The configured setup exhibits multiple effects, concurrently improving plasmonic and fluorescence responses under solar irradiation, thereby enhancing energy conversion performance. Integrating plasmonic nanostructures with OSCs can address fundamental issues, providing opportunities to enhance the light-absorption intensity and charge transfer efficiency at intra and intermolecular levels. This comprehensive review demonstrates that the greatest improvement in solar cell efficiency exceeded 30% compared with the reference cells.

Orchestration of ferro- and anti-ferromagnetic ordering in gold nanoclusters.

The unpaired electron in the gold clusters (Aun, n = no. of Au atoms) with an odd number of total electrons is solely responsible for the magnetic properties in the small-sized Au nano-clusters. However, no such unpaired electron is available due to pairing in the even number of atom gold clusters and behaving as a diamagnetic entity similar to bulk gold. In this work, we unveiled the spin-density distribution of odd Aun clusters with n = 1 to 19 that reveals that a single unpaired electron gets distributed non-uniformly among all Au-atoms depending on the cluster size and morphology. The delocalization of the unpaired electron leads to the spin dilution approaching a value of ∼1/n spin moments on each atom for the higher clusters. Interestingly, small odd-numbered gold clusters possess spin-magnetic moments similar to the delocalized spin moments as of organic radicals. Can cooperative magnetic properties be obtained by coupling these individual magnetic gold nanoparticles? In this work, by applying state-of-the-art computational methodologies, we have demonstrated ferromagnetic or anti-ferromagnetic couplings between such magnetic nanoclusters upon designing suitable organic spacers. These findings will open up a new avenue of nanoscale magnetic materials combining organic spacers and odd-electron nano-clusters.

Investigation of vibrational changes due to adsorption of glycine on gold

The affinity of glycine to gold nanoparticles in aqueous environments is of importance in a wide range of applications including protein engineering and wet chemical synthesis. In an aqueous environment, glycine exists predominantly as a zwitterion, however, the adsorption of zwitterionic glycine on gold and its impact on the vibrational spectra has not been well studied. This work uses density functional theory to investigate the adsorption of neutral and zwitterionic glycine molecules on two-, four-, six- and 20-atom gold clusters. The neutral glycine molecule preferentially binds to gold via the amine group rather than via the carboxyl group, with interaction energies ranging from 21 down to ≈11 kcalmol−1 for two to 20 atom gold clusters, respectively. For the zwitterion in an implicit solvent medium, binding can only occur via the carboxyl group. The interaction energy ranges from 23 to 13 kcalmol−1 for two to 20-atom gold clusters, respectively. Bader charges analysis and charge difference density maps show that electronic charge is transferred to the gold cluster. Vibrational frequencies and IR intensities were calculated for neutral and zwitterionic glycine and for all binding configurations on the gold clusters. The IR spectra of both neutral and zwitterion glycine molecules show the sharpest peak for C–O stretching modes. This C–O stretching mode redshifts by around 100 cm−1 neutral glycine binds via carboxyl group. In the case of the zwitterion, the sharpest peak remains at the same position after adsorption. The size of the gold cluster has a negligible impact on the vibrational IR spectra for both neutral and zwitterion glycine molecules.

Array of Miniaturized Amperometric Gas Sensors Using Atomic Gold Decorated Pt/PANI Electrodes in Room Temperature Ionic Liquid Films.

Miniaturized sensors possess many advantages, such as rapid response, easy chip integration, a possible lower concentration of target compound detection, etc. However, a major issue reported is a low signal response. In this study, a catalyst, the atomic gold clusters of Aun where n = 2, was decorated at a platinum/polyaniline (Pt/PANI) working electrode to enhance the sensitivity of butanol isomers gas measurement. Isomer quantification is challenging because this compound has the same chemical formula and molar mass. Furthermore, to create a tiny sensor, a microliter of room-temperature ionic liquid was used as an electrolyte. The combination of the Au2 clusters decorated Pt/PANI and room temperature ionic liquid with several fixed electrochemical potentials was explored to obtain a high solubility of each analyte. According to the results, the presence of Au2 clusters increased the current density due to electrocatalytic activity compared to the electrode without Au2 clusters. In addition, the Au2 clusters on the modified electrode had a more linear concentration dependency trend than the modified electrode without atomic gold clusters. Finally, the separation among butanol isomers was enhanced using different combination of room-temperature ionic liquids and fixed potentials.

Adsorption of air pollutants onto silver and gold atomic clusters: DFT and PNO-LCCSD-F12 calculations.

We provide a comprehensive investigation of intermolecular interactions between atmospheric gaseous pollutants, including CH4, CO, CO2, NO, NO2, SO2, as well as H2O and Agn (n = 1-22) or Aun (n = 1-20) atomic clusters. The optimized geometries of all the systems investigated in our study were determined using density functional theory (DFT) with M06-2X functional and SDD basis set. The PNO-LCCSD-F12/SDD method was used for more accurate single-point energy calculations. Compared to their isolated states, the structures of the Agn and Aun clusters undergo severe deformations upon adsorption of the gaseous species, which become more significant as the size of the clusters decreases. Considering that, in addition to adsorption energy, we have determined the interaction and deformation energy of all the systems. All our calculations consistently show that among the gaseous species examined, SO2 and NO2 exhibit a higher preference for adsorption on both types of clusters, with a slightly higher preference for the Ag clusters compared to the Au clusters, with the SO2/Ag16 system exhibiting the lowest adsorption energy. The type of intermolecular interactions was investigated through wave function analyses, including natural bond orbital (NBO) and quantum theory of atoms in molecules (QTAIM), showing that NO2 and SO2 are chemisorbed on the Agn and Aun atomic clusters, whereas the other gas molecules exhibit a much weaker interaction with them. The reported data can be used as input parameters for molecular dynamics simulations to study the selectivity of atomic clusters towards specific gases under ambient conditions, as well as to design materials that take advantage of the studied intermolecular interactions.

Luminescent gold nanocluster-decorated polymeric hybrid particles for laser guided therapy

Gold nanoclusters or ultrasmall gold atom clusters (AuNCs, <2 nm in diameter) exhibit emergent photonic properties in the near-infrared (NIR) spectrum due to the quantization of their conduction band. This gives rise to attractive NIR luminescent properties that offer great promises for imaging and diagnostic purposes in biomedical applications. AuNCs also absorb NIR light in the biological window inducing photothermal events that can facilitate localized drug release and synergistic thermal therapy. Here, we designed a micellar system based on poly(ethylene glycol) (PEG) and thermosensitive poly(N-isopropylacrylamide) (PNIPAM) copolymerized with functional monomers to allow for micellar core-crosslinking via oxo-ester mediated native chemical ligation (OMNCL). These micelles are decorated with AuNCs (<2 nm) and covalently bound thiolated doxorubicin, which allow for both precise intracellular imaging as well as light-induced cell killing. The polymer bound AuNCs exhibit a NIR luminescent emission maximum at ~ 720 nm with a quantum yield of ~ 3%. Internalization studies of the micellar system on MDA-MB-231 cancer cells showed that doxorubicin remains bound within the micelles in the cytosolic region after 24 h incubation. Upon NIR light irradiation at 650 nm, highly localized cell death is observed, which is limited only to the irradiated area. This innovative hybrid material design of the the AuNC-decorated micelles enables an efficient combination of live imaging and precisely controlled therapy.

Characterization of atmospheric-pressure spark generated atomic silver and gold clusters by time-of-flight mass spectrometry

The potential of using atmospheric-pressure spark ablation for production of atomic clusters has been shown in the recent past. In this study we used this method to produce atomic clusters in Argon and investigated their chemical composition with an atmospheric pressure interface time-of-flight mass spectrometer (APi-TOF-MS). Both anionic and cationic silver and gold clusters were generated and characterised. The carrier gas was used directly from the gas cylinder without the application of any additional gas purification. As a result, the carrier gas stream contained trace impurities of N2, O2, and H2O, as well as radicals such as O, OH, and H and their ionized forms resulting from the plasma created by the sparks. The experimental results show that different reactivities towards oxygen and water traces can be observed depending on the number of metal atoms in the clusters, their polarity, as well as their compositions; e.g., Aun− shows less reactive behaviour towards oxygen and hydrogen compared to Agn−. The results also show that certain cluster types can be generated at large enough quantities by atmospheric-pressure spark ablation, which considering the low installation and operating cost of the technique can pave the way towards its exploitation for numerous technological applications.

Polyaniline Supported Atomic Gold Electrode Toward Glucose Oxidation

Gold is reported to have unique catalytic properties for oxidization of alcohols in alkaline media, and the catalytic ability is dependent on size of the gold, which enhancement in the catalytic activity is observed following reduction of the size [1]. As size of the gold reduced to atomic level, the property would vary depending on the number of atoms in a gold cluster [1, 2]. For instance, the alcohol oxidation catalytic activity is promoted when there is an even number of gold atoms in a cluster and demoted when the gold cluster contains odd number of atoms [1, 3]. Simulation results indicate that the HOMO-LUMO gap switches between conductor and semi-conductor when the atom number changes [2]. Deposition of atomic level gold clusters is realized by a cyclic atomic gold deposition process utilizing polyaniline (PANI) as the supporting substrate [1, 3]. In this study, PANI decorated with different numbers of gold atoms is prepared, and effect of the gold atom number in glucose oxidation is evaluated for application in glucose electrochemical sensor.Figure 1 shows the fabrication process of the PANI/Au electrode. The PANI was prepared by electropolymerization on a pretreated platinum electrode. The electrolyte was composed of 0.1 M aniline monomer in 2 M HBF4. Color of the surface of the Pt electrode changed from silver to blue after the polymerization process. Thereafter, KAuCl4 was used as source of the gold in the cyclic atomic gold deposition process. Figure 2 shows sequence of the cyclic atomic deposition process for gold. In one cycle of the deposition, one and only one gold ion was attracted to an amine group in the PANI, and the attracted gold ion was reduced to form a gold atom. After preparation of the PANI/Au N (N indicates the number of the deposition cycle conducted) electrode, glucose oxidase (GOD) was immobilized as an enzyme on the electrode surface by a comprehensive crosslinking method.Figure 3 shows cyclic voltammogram (CV) results of glucose oxidation on the PANI/Au2 electrode when the glucose concentration in a phosphate buffer solution (PBS) was varied from 0 to 20 mM. Anodic current generated from oxidation of the glucose was confirmed when the concentration was higher than 5 mM. In order to reveal effects of the gold atom number on oxidation of glucose, PANI/Au N electrodes with the N changed from 1 to 3 were prepared. In the CV scans, a scan rate of 50 mV/s and 10.0 mM glucose were used. Figure 4 shows the CV results when using the PANI/Au N electrode as the working electrode. Anodic current caused by oxidation of glucose was observed in all the three electrodes. The current response increased when the deposition cycle was increased from 1 to 2, and the PANI/Au3 produced current responses between those of the PANI/Au1 and PANI/Au2. This implies that the glucose oxidation is lowered when an odd number of gold atoms is deposited. [1] Alex P. Jonke, Mira Josowicz and Jiří Janata, J. Electrochem. Soc. 159 2012 40-43. [2] E. M. Fernandez, J. M. Soler, I. L. Garzon, L. C. Balbas, Phys. Rev. B 70 2004 165403. [3] J. Janata, T. Nakamoto, IEEJ Transaction 11 2016 261-267. Figure 1

Indirect Sensing of Lower Aliphatic Ester Using Atomic Gold Decorated Polyaniline Electrode.

Novel sensing materials have been formed by decorating polyaniline conducting polymers with atomic gold clusters where the number of atoms is precisely defined. Such materials exhibit unique electrocatalytic properties of electrooxidation to aliphatic alcohols, although analytes with other functional groups have not been studied. This paper reports a study of cyclic voltammetric patterns obtained with bi-atomic gold nanocomposite response to analytes with other functional groups for sensor applications. Principal component analysis shows separation among normal-propanol, iso-propanol and ethyl formate/ethanol groups. Indirect sensing of ethyl formate is demonstrated by electrooxidation of the product upon hydrolysis in alkaline medium. Voltammograms of ethyl formate are studied in gaseous phases.

Tailoring the luminescence of atomic clusters via ligand exchange reaction mediated post synthetic modification.

The growing prominence of atomic nanoclusters in fields of practical relevance has made modulation of their luminescent characteristics an important challenge for their future applications. Herein we report chemical reaction assisted modulation of luminescence of histidine stabilized gold nanoclusters via a ligand exchange reaction with cysteine. Upon addition of 3.8 mM cysteine, as evinced by X-ray photoelectron spectroscopy in conjunction with transmission electron microscopic analyses, histidine molecules were found to desorb from the surface of the Au NCs leading to the latter's aggregation into macroscopic units. Consequently, the luminescence of the His Au NCs underwent a large bathochromic shift from 475 nm to 500 nm with a concomitant decrease in the luminescence intensity. Thereafter, upon addition of 18 mM cysteine to a dispersion of His Au NCs, cysteine molecules by virtue of strong aurophilic interactions were found to adsorb on to the surface of the Au NCs, leading to the disaggregation of the macroscopic structures. This was accompanied by restoration of the luminescence features of the Au NCs to an emission maximum of 486 nm with partial recovery of the luminescence intensity. Thus, the work embodied herein demonstrates post-synthetic chemical reactions of nanoclusters as an effective and viable tool for tailoring the photoluminescence of atomic clusters to meet application demands.

The Effects of Photodynamic Therapy Using Green Laser and Glutathione-Capped-Gold Nanoparticles on Cancer Cells (MCF-7 Cell Line)

Background: Nanotechnology is a discipline that manages, constructs, analyzes and deals with application of materials that have diameter from 1 to 100 nanometers. Gold nanoparticles are defined as stable colloid solutions of clusters of gold atoms with sizes at this minuscule. Objective: The objective of current study was to treat breast cancer using gold nanoparticles capped with drug molecules in specific quantities to reduce the harmful side effects. Method: The gold nanoparticales were prepared by method of Brust-Schiffrin. These nanoparticles were capped with type of drug (Glutathione) used to treat cancerous tumors. These gold nanoparticles were uncapped with drugs at (526nm) when capped with the glutathione drug at (589nm). Results: The resulting evidence suggested that Glutathione-capped Gold nanoparticles were non-toxic up to the maximum recommended dosage. Therefore, the demonstrated biocompatibility offers the potentials of Glutathione-capped with Gold nanoparticles.The candidate is considered as a medicine for cancer therapy.

Bonding Forces and Energies on the Potential Energy Surface (PES) of the Optimized Gold Atomic Clusters at the Gradient (ds = 0.01 a.u.)

Bonding Forces and Energies on the Potential Energy Surface (PES) of the Optimized Gold Atomic Clusters at the Gradient (ds = 0.01 a.u.)

Glutathione-capped gold nanoclusters: photoinduced energy transfer and singlet oxygen generation $$^{\S }$$ §

Glutathione-capped gold clusters prepared in an aqueous medium are known to exhibit excellent photosensitizing properties. We have now successfully transferred these gold clusters in an organic medium while retaining all the characteristic excited state properties. These gold clusters can be further modified with organic ligands such as 2-Phenylethanethiol (PET). The gold clusters in organic medium exhibit enhanced emission yield ( $$\Phi _{\mathrm{f}} = 0.15$$ ) compared to that in an aqueous medium ( $$\Phi _{\mathrm{f}} = 0.08$$ ). The excited state lifetimes of $$3.7\,\upmu \hbox {s}$$ (untreated) and $$1.5\,\upmu \hbox {s}$$ (PET treated) in toluene are also greater than the lifetime observed in aqueous solution ( $$0.77\,\upmu \hbox {s}$$ ). By employing laser flash photolysis we are able to induce triplet energy transfer to $$\upbeta $$ -carotene and oxygen. A singlet oxygen generation with the efficiency of 13% was observed in these experiments. The excited state properties of glutathione-capped gold clusters further shows its importance as a photosensitizer in light energy conversion and biomedical applications SYNOPSIS A few atom gold clusters modified with organic ligands exhibit high photoactivity by generating singlet oxygen with 13% quantum efficiency.

Formation of positive and negative clusters of gold atoms inside helium nanodroplets close to zero K

We report the mass spectrometric detection of positive and negative cluster ions of gold atoms formed by the pickup of gold by helium nanodroplets (HNDs) near zero K and subsequent exposure to electron impact. Both singly and doubly charged positive cluster ions were observed. Ionization is initiated by the helium ions He+ and He*−, metastable helium atoms He* as well as electron attachment. We focus on the size distributions of the ions, electron energy dependence of ion yield, patterns of stability and the presence of “magic” clusters. As reported previously by others using a variety of other methodologies, a clear oscillation in the intensity of (Au)n+/- is seen, especially for n <21, with odd-numbered clusters being more intense than even-numbered clusters. The distributions peak early around n = 8. There is a suggestion of magic numbers at n = 35 and 58. Efficiencies of formation of the gold cluster anions were monitored as a function of the energy of the electrons; the measured intensity distributions exhibit a shift to higher energies with increasing cluster size that is attributed to the need to evaporate helium from the clusters for their observation in the nascent state.

Generalized Breit-Wigner treatment of molecular transport: Charging effects in a single decanedithiol molecule.

We examine the relative contribution of ballistic and elastic cotunneling mechanisms to the charge transport through a single decanedithiol molecule linked to two terminal clusters of gold atoms. For this, we first introduced a conceptual model that permits a generalization of the Breit-Wigner scattering formalism where the cation, anion, and neutral forms of the molecule can participate with different probabilities of the charge transfer process, but in a simultaneous manner. We used a density functional theory treatment and considered the fixed geometry of each charge state to calculate the corresponding eigenvalues and eigenvectors of the extended system for different values of the external electric field. We have found that for the ballistic transport the HOMO and LUMO of the neutral species play a key role, while the charged states give a negligible contribution. On the other hand, an elastic cotunneling charge transfer can occur whenever a molecular orbital (MO) of the cation or anion species, even if localized in just one side of the molecule-gold clusters complex, has energy close to that of a delocalized MO of the neutral species. Under these conditions, a conduction channel is formed throughout the entire system, in a process that is controlled by the degree of resonance between the MOs involved. Our results indicate that while different charge transfer mechanisms contribute to the overall charge transport, quantum effects such as avoided-crossing situations between relevant frontier MOs can be of special importance. In these specific situations, the interchange of spatial localization of two MOs involved in the crossing can open a new channel of charge transfer that otherwise would not be available.

Luminescent Gold Nanocluster-Decorated Polymeric Hybrid Particles with Assembly-Induced Emission.

Ultrasmall gold atom clusters (<2 nm in diameter) or gold nanoclusters exhibit emergent photonic properties (near-infrared absorption and emission) compared to larger plasmonic gold particles because of the significant quantization of their conduction band. Although single gold nanocluster properties and applications are being increasingly investigated, little is still known about their behavior and properties when assembled into suprastructures, and even fewer studies are investigating their use for biomedical applications. Here, a simple synthetic pathway combines gold nanoclusters with thermosensitive diblock copolymers of poly(ethylene glycol) (PEG) and poly(N-isopropylacrylamide) (PNIPAm) to form a new class of gold-polymer, micelle-forming, hybrid nanoparticle. The nanohybrids’ design is uniquely centered on enabling the temperature-dependent self-assembly of gold nanoclusters into the hydrophobic cores of micelles. This nonbulk assembly not only preserves but also enhances the attractive near-infrared photonics of the gold nanoclusters by significantly increasing their native fluorescent signal. In parallel to the fundamental insights into gold nanocluster ordering and assembly, the gold-polymer nanohybrids also demonstrated great potential as fluorescent live-imaging probes in vitro. This innovative material design based on the temperature-dependent, self-assembly of gold nanoclusters within a polymeric micelle’s core shows great promise toward bioassays, nanosensors, and nanomedicine.

Gold atomic cluster mediated electrochemical aptasensor for the detection of lipopolysaccharide

We have constructed an aptamer immobilized gold atomic cluster mediated, ultrasensitive electrochemical biosensor (Apt/AuAC/Au) for LPS detection without any additional signal amplification strategy. The aptamer self-assemble onto the gold atomic clusters makes Apt/AuAC/Au an excellent platform for the LPS detection. Differential pulse voltammetry and EIS were used for the quantitative LPS detection. The Apt/AuAC/Au sensor offers an ultrasensitive and selective detection of LPS down to 7.94 × 10–21M level with a wide dynamic range from 0.01 attomolar to 1pM. The sensor exhibited excellent selectivity and stability. The real sample analysis was performed by spiking the diluted insulin sample with various concentration of LPS and obtained recovery within 2% error value. The sensor is found to be more sensitive than most of the literature reports. The simple and easy way of construction of this sensor provides an efficient and promising detection of an even trace amount of LPS.

Thermal transport at a solid-nanofluid interface: from increase of thermal resistance towards a shift of rapid boiling.

We use molecular dynamics simulations to investigate interfacial thermal transport between an ethanol suspension containing gold atomic clusters and a gold surface, using both realistic and simplified molecular models of nanoparticles. The interfacial thermal conductance was determined via a thermal relaxation method for a variety of nanoparticle-nanoparticle and nanoparticle-surface interaction strengths. The Kapitza resistance is found to increase due to the presence of nanoparticles in the vicinity of the solid-liquid interface. The heat flow from the solid to the nanoparticles is separated from its counterpart from the solid to the liquid to discriminate their respective contribution to the total heat current. A per-vibrational-mode analysis highlights a shift of major heat carriers from low frequencies towards higher frequencies due to the coupling of the internal nanoparticle dynamics to the gold surface, in addition to stronger particle-surface interactions. Finally, we demonstrate that the increase of the Kapitza resistance significantly shifts the nanofluid/solid surface explosive boiling temperature to higher temperatures compared to pure ethanol.

Biomimetically crystallized protease resistant zinc phosphate decorated with gold atomic clusters for bioimaging

A luminescent probe synthesised via biomimetic crystallization of zinc phosphate in the presence of protein fragment stabilised gold (Au) nanoclusters is reported. The engineered probe - with Au nanoclusters assembled on the crystal - was protease resistant and offered efficient bioimaging and uptake studies.