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Candida aurisis an emerging pathogenic fungus implicated in healthcare-associated outbreaks and causes bloodstream infections associated with high mortality rates. Biofilm formation represents one of the major pathogenetic traits associated with this microorganism. Unlike most other Candidaspecies, C. aurishas the ability to survive for weeks on different surfaces. Therefore, there is an urgent need to develop new effective control strategies to combat the threat of C. auris. Advances in nanotechnologies have emerged that carry significant potential impact against Candidabiofilms. We obtained pure round silver nanoparticles (AgNPs) (1 to 3 nm in diameter) using a microwave-assisted synthetic approach. When tested against C. auris, our results indicated a potent inhibitory activity both on biofilm formation (half maximal inhibitory concentration (IC50) of 0.06 ppm) and against preformed biofilms (IC50of 0.48 ppm). Scanning electron microscopy images of AgNP-treated biofilms showed cell wall damage mostly by disruption and distortion of the outer surface of the fungal cell wall. In subsequent experiments AgNPs were used to functionalize medical and environmental surfaces. Silicone elastomers functionalized with AgNPs demonstrated biofilm inhibition (>50%) at relatively low concentrations (2.3 to 0.28 ppm). Bandage dressings loaded with AgNPs inhibited growth of C. aurisbiofilms by more than 80% (2.3 to 0.017 ppm). Also, to demonstrate long-lasting protection, dressings loaded with AgNPs (0.036 ppm) were washed thoroughly with phosphate-buffered saline, maintaining protection against the C. aurisgrowth from cycles 1 to 3 (>80% inhibition) and from cycles 4 to 6 (>50% inhibition). Our results demonstrate the dose-dependent activity of AgNPs against biofilms formed by C. aurison both medical (silicone elastomer) and environmental (bandage fibers) surfaces. The AgNPs-functionalized fibers retain the fungicidal effect even after repeated thorough washes. Overall these results point to the utility of silver nanoparticles to prevent and control infections caused by this emerging pathogenic fungus.

Metallic nanoparticles display unique optical, electronic, and chemical properties compared to their bulk counterparts. These properties are influenced by the internal structure of nanoparticles. Therefore, atomic structural characterization of nanoparticles is of paramount importance in nanotechnology. In this work, we present the synthesis, mass spectrometry, and structural characterization of highly monodisperse thiolate-protected gold nanoparticles (∼3.8 nm) using aberration-corrected scanning transmission electron microscopy (STEM). Mass spectrometry reveals the composition to be Au∼2000(SC6H13)∼290. The images registered in the high-angle annular dark field detector (HAADF–STEM) showed the presence of decahedral and single-crystal face-centered cubic (fcc) nanoparticles as well as fcc structures with multiple planar defects. We also observed nanoparticles with an inner grain boundary corresponding to a high-angle grain boundary classified as Σ9 under the coincidence site lattice notation. Experimental structural analysis and characterization of grain boundaries were correlated with simulated HAADF–STEM images of structural models for Σ9. The present report demonstrates the coexistence of two crystallites within thiolate-protected nanoparticles separated by high-angle grain boundaries.

Electrochemical oxygen reduction reaction (ORR) catalysts that have both high activities and long-term stabilities are needed for proton-exchange membrane fuel cells (PEMFCs) and metal–air batteries. Two-dimensional (2D) materials based on graphene have shown high catalytic activities, however, carbon-based materials result in significant catalyst degradation due to carbon oxidation that occurs at high electrochemical potentials. Here, we introduce the synthesis and electrochemical performance of metallic 2D nanoframes which represent a new approach to translate 2D materials into unsupported (carbon-free) electrocatalysts that have both significantly higher ORR catalytic activities and stabilities compared with conventional Pt/carbon electrocatalysts. Metallic Ni–Pt 2D nanoframes were synthesized by controlled thermal treatments of Pt-decorated Ni(OH)2nanosheets. The nanoframes consist of a hierarchical 2D framework composed of a highly catalytically active Pt–Ni alloy phase with an interconnected solid and pore network that results in three-dimensional molecular accessibility. The inclusion of Ni within the Pt structure resulted in significantly smaller Pt lattice distances compared to those of Pt nanoparticles. On the basis of its unique local and extended structure, the ORR specific activity of Ni–Pt 2D nanoframes (5.8 mA cmPt–2) was an order of magnitude higher than Pt/carbon. In addition, accelerated stability testing at elevated potentials up to 1.3 VRHEshowed that the metallic Ni–Pt nanoframes exhibit significantly improved stability compared with Pt/carbon catalysts. The nanoarchitecture and local structure of metallic 2D nanoframes results in high combined specific activity and elevated potential stability. Analysis of the ORR electrochemical reaction kinetics on the Ni–Pt nanoframes supports that at low overpotentials the first electron transfer is the rate-determining step, and the reaction proceeds via a four electron reduction process. The ability to create metallic 2D structures with 3D molecular accessibility opens up new opportunities for the design of high activity and stability carbon-free catalyst nanoarchitectures for numerous electrocatalytic and catalytic applications.

The protected noble-metal structures comprising 145 metal-atom sites and 60 ligands are among the frequently identified larger metal-cluster systems exploited in many avenues of research. Herein we report a comparative electrospray ionization-mass spectrometry (ESI-MS) investigation of the 60-fold thiolated Au144and CuAu144clusters, in various positive charge-states, in conjunction with a density-functional theoretical (DFT) analysis based upon the icosahedral Pd145-structure-type applicable to these systems. Samples rich in the hexanethiolate-protected CuAu144clusters are obtained via a single-phase reduction process. The predicted electronic structure of the vacancy-centered Au144(SR)60system provided a simple rationale for the limiting [4+] charge-state observed of Au144, whereas the maximal [3+] charge detected on the CuAu144(SR)60cluster can be explained if the 145th atom occupies the central site. Occupancy of the center-site stabilizes the superatomic 3S-orbital, and thereby shifts the shell-closing count from 82 to 84 free electrons. The DFT-calculated energetics also predicts a strong (0.65 eV) preference for placing the smaller Cu ion in this central site. Remarkably, the optical absorption spectra of dilute tetrahydrofuran (THF) solutions feature a broad band centered near 2.3 eV, in contrast to the previously reported “nonplasmonic” response of sub-2.0-nm all-gold or -copper clusters. Other methods (matrix-assisted laser desorption ionization mass spectrometry and high-resolution electron microscopy) were used to investigate whether aggregation phenomena might account for this observed plasmon emergence. This unusual result points to the need to obtain highly purified samples of copper-doped gold clusters of ca. 145 atoms total.

This study addresses how ligands module the structure and the electronic optical properties of a large set of the experimentally known anionic thiolate-protected gold clusters, Au25(SR)18[1−]. Starting from the experimental crystal structure, computational density functional theory calculations reveal that low-polarity R groups do not disturb the Au25S18framework significantly, such that the inversion symmetry(Ci) of the crystalline state is retained. In the case of p-thiolphenolate ligands, p-SPhX, a major distortion of the Au25S18framework, destroys the inversion symmetry, the distortion increasing in the order given X = H, Cl, NO2and CO2H. For branched R groups, linking −CH3or −NH2groups at the two-position of the phenylethylthiolate ligand, the inversion symmetry is retained and lost, respectively; similarly, the N-acetyl-cysteine ligand also distorts the framework. These results demonstrate a systematic preference of inversion-symmetric versus nonsymmetric framework depending on the ligand-type. The more distorted structures also exhibit significantly reduced HOMO–LUMO gap values and affect the optical absorption spectra accordingly. This study correlates the distortion of the Au25S18framework with the structure, electronic, and optical properties among the studied clusters.

Abstract

This report addresses a density functional theory study of the vibrational normal modes of small-sized thiolate-protected gold clusters. Calculated far-infrared (far-IR) and low-frequency Raman spectra of established thiolate-protected gold clusters (4, 12, 18, 19, 20, 24, and 25 Au atoms) show characteristic peaks in the range of 20–350 cm–1that can be attributed to the breathing mode of the gold core, Au–S–Au bending modes and Au–S stretching modes. It was found that as cluster size increases the Au13breathing mode of Au25cluster emerges. This study reveals both systematic and specific characteristics that may provide a basis for identification (“fingerprinting”) by far-IR and low-frequency Raman spectroscopy of the many diverse gold–thiolate cluster compounds.

Bimetallic nanoparticles present different properties than their monometallic counterparts, opening a wide range of possibilities for different applications. PtPd nanoparticles have raised interest for their many applications in fuel cells, ethanol and methanol oxidation reactions, hydrogen storage, and so on. However, the cost of Pt makes it unpractical to use in big quantities; therefore, one of the big challenges is to synthesize very small catalysts in order to maximize the efficiency in their use. In this work, we synthesized polyhedral PtPd core–shell nanoparticles under 20 nm and characterized them by Cs-corrected scanning transmission electron microscopy. This technique allowed us to probe the structure at the atomic level of these nanoparticles revealing new structural information. We determined the structure of the three main polyhedral morphologies obtained in the synthesis: octahedral, decahedral, and triangular plates. Decahedral PtPd core–shell nanoparticles are novel morphologies for this system. Morphology and defects present in the nanoparticles are shown and discussed.

The stability of decahedral shaped nanoparticles depends upon size. Ino and Marks introduced new mechanisms for the stabilization of decahedra nanoparticles that involves the faceting and formation of surfaces different from {111}. These mechanisms have relevance for small size nanoparticles; however, they do not thoroughly explain how decahedral particles can grow up to 300 nm or more. Here, we report new mechanisms that help stabilize very large decahedra. With the use of aberration-corrected scanning transmission electron microscopy, we observed the formation of high index facets, determined to be of the {511} family, on all five sides of the particles. Surface dislocations strings are also observed. In addition, surface reconstruction of the {001} surfaces can also be observed in two different orientations: with hexagonal strings along the [110] and [410] directions.

The Debye temperature of Pt nanoparticles (NP) capped in PVP-K30 with an average diameter of 3 nm was determined from extended X-ray absorption fine structure measurements between 20 and 373 K. The size distribution of the NP was determined by high-resolution transmission electron microscopy, high-angle annular dark field, and small-angle X-ray scattering. We have experimentally established that the Debye temperature of truncated cuboctahedron, capped Pt NP is 70 K higher than that of bulk Pt metal. The rather high value of the Debye temperature of nanosized-capped Pt crystals is related to surface Pt−Pt contraction effects in conjunction with capping interactions. This finding evidences that the vibrational behavior of nanostructure materials differs markedly from that of materials in bulk form.

Oat (Avena sativa) biomass was studied as an alternative to recover Au(III) ions from aqueous solutions and for its capacity to reduce Au(III) to Au(0) forming Au nanoparticles. To study the binding trend of Au(III) to oat and the possible formation of Au nanoparticles, the biomass and a solution of Au(III) were reacted for a period of 1 h at pH values ranging from 2 to 6. The results demonstrated that Au(III) ions were bound to oat biomass in a pH-dependent manner, with the highest adsorption (about 80%) at pH 3. HRTEM studies showed that oat biomass reacted with Au(III) ions formed Au nanoparticles of fcc tetrahedral, decahedral, hexagonal, icosahedral multitwinned, irregular, and rod shape. To our knowledge, this is the second report about the production of nanorods as a product of the reaction of a Au(III) solution with a biological material. These studies also showed that the pH of the reaction influenced the nanoparticle size. The smaller nanoparticles and the higher occurrence of these were observed at pH values of 3 and 4, whereas the larger nanoparticles were observed at pH 2.

We report the growth and materials characterization of thin (<35 nm) germanium-carbon alloy (GeC) layers grown directly on Si by ultra-high-vacuum chemical vapor deposition. We show that the presence of C atoms is limited to a thin interfacial region at the Si substrate, and interpret this result as a mechanism for strain relief. We also show that the GeC films exhibit remarkably low threading dislocation densities despite significant relaxation.