Gold Nanoparticles of Diameter 1.4 nm Trigger Necrosis by Oxidative Stress and Mitochondrial Damage

Gold nanoparticles (AuNPs) are generally considered nontoxic, similar to bulk gold, which is inert and biocompatible. AuNPs of diameter 1.4 nm capped with triphenylphosphine monosulfonate (TPPMS), Au1.4MS, are much more cytotoxic than 15‐nm nanoparticles (Au15MS) of similar chemical composition. Here, major cell‐death pathways are studied and it is determined that the cytotoxicity is caused by oxidative stress. Indicators of oxidative stress, reactive oxygen species (ROS), mitochondrial potential and integrity, and mitochondrial substrate reduction are all compromised. Genome‐wide expression profiling using DNA gene arrays indicates robust upregulation of stress‐related genes after 6 and 12 h of incubation with a 2 × IC50 concentration of Au1.4MS but not with Au15MS nanoparticles. The caspase inhibitor Z‐VAD‐fmk does not rescue the cells, which suggests that necrosis, not apoptosis, is the predominant pathway at this concentration. Pretreatment of the nanoparticles with reducing agents/antioxidants N‐acetylcysteine, glutathione, and TPPMS reduces the toxicity of Au1.4MS. AuNPs of similar size but capped with glutathione (Au1.1GSH) likewise do not induce oxidative stress. Besides the size dependency of AuNP toxicity, ligand chemistry is a critical parameter determining the degree of cytotoxicity. AuNP exposure most likely causes oxidative stress that is amplified by mitochondrial damage. Au1.4MS nanoparticle cytotoxicity is associated with oxidative stress, endogenous ROS production, and depletion of the intracellular antioxidant pool.     

Cytotoxicity of Ultrasmall Gold Nanoparticles on Planktonic and Biofilm Encapsulated Gram‐Positive Staphylococci

The emergence of multidrug resistant bacteria, especially biofilm‐associated Staphylococci, urgently requires novel antimicrobial agents. The antibacterial activity of ultrasmall gold nanoparticles (AuNPs) is tested against two gram positive: S. aureus and S. epidermidis and two gram negative: Escherichia coli and Pseudomonas aeruginosa strains. Ultrasmall AuNPs with core diameters of 0.8 and 1.4 nm and a triphenylphosphine‐monosulfonate shell (Au0.8MS and Au1.4MS) both have minimum inhibitory concentration (MIC) and minimum bactericidal concentration of 25 × 10^?6m [Au]. Disc agar diffusion test demonstrates greater bactericidal activity of the Au0.8MS nanoparticles over Au1.4MS. In contrast, thiol‐stabilized AuNPs with a diameter of 1.9 nm (AuroVist) cause no significant toxicity in any of the bacterial strains. Ultrasmall AuNPs cause a near 5 log bacterial growth reduction in the first 5 h of exposure, and incomplete recovery after 21 h. Bacteria show marked membrane blebbing and lysis in biofilm‐associated bacteria treated with ultrasmall AuNP. Importantly, a twofold MIC dosage of Au0.8MS and Au1.4MS each cause around 80%–90% reduction in the viability of Staphylococci enveloped in biofilms. Altogether, this study demonstrates potential therapeutic activity of ultrasmall AuNPs as an effective treatment option against staphylococcal infections.     

Effects of Polymeric Stabilizers on the Synthesis of Gold Nanoparticles

Gold nanoparticles （AuNPs） stabilized with sodium alginate （SA）, glycol chitosan （GC）, polyvinyl alcohol （PVA）, and polyethyleneimine （PEI） were synthesized in aqueous solutions at room temperature. Different sizes and size distributions of AuNPs were obtained according to the polymeric stabilizers. The mean particle diameters of AuNPs synthesized with GC and PVA as stabilizers were about 5.1 and 5.3 nm, respectively, while those of AuNPs stabilized with SA and PEI were 8.4 and 10.8 nm, respectively. When SA was used, relatively large particles aggregated to form large clusters. In the case of GC, a number of small particles built up large clusters. When PVA was used, the size and the number of nanoperticles were estimated small with a low weight content of Au. For this reason, the PVA-stabilized AuNPs formed clusters with a small hydrodynamic size. The AuNPs synthesized in the aqueous solution of PEI without a reducing agent, sodium borohydride, were uniform in size and formed the smallest nanoclusters （67.4 nm）. In this case, the highest Au content was obtained. Sufficiently grown nanoparticles with a high Au content and a limited hydrodynamic size are considered to be suitable for a variety of applications.     

Bidirectional Regulation of Singlet Oxygen Generation from Luminescent Gold Nanoparticles through Surface Manipulation

Singlet oxygen (¹O₂) generation has been observed from ultrasmall luminescent gold nanoparticles (AuNPs), but regulation of ¹O₂ generation ability from the nanosized noble metals has remained challenging. Herein, the ¹O₂ generation ability of ultrasmall AuNPs (d ≈ 1.8 nm) is reported to be highly correlated to the surface factors including the amount of Au(I) species and surface charge. By taking the advantages of facile in situ PEGylation, it is discovered that a high amount of Au(I) species and surface charge results in strong ability in generation of ¹O₂, whereas a relative low amount of Au(I) species and surface charge leads to weak ability in ¹O₂ production. A feasible general strategy is then developed to controllably regulate the ¹O₂ generation efficiency of the AuNPs through facile ligand exchange with positively‐charged or negatively‐charged thiolated ligands. The AuNPs as nanophotosensitizer for ¹O₂ generation in the cellular level is also demonstrated to be highly controllable through surface ligand exchange with synergistical effects of ¹O₂ generation ability and subcellular distribution to lysosome or mitochondria. The strategy in the bidirectional regulation of ¹O₂ generation from ultrasmall AuNPs provides guidance for future design of nanosized metal nanomedicine toward specific disease diagnosis and treatment.     

Magnesia supported Au and Ag catalysts for the preparation of few-layer graphene–metal nanocomposites: relationship between catalyst structure and the properties of graphene composites

Magnesia supported Au, Ag, and Au–Ag nanostructured catalysts were prepared, characterized, and used to synthesize few-layer graphene–metal nanoparticle (Gr–MeNP) composites. The catalysts have a mezoporous structure and a mixture of MgO and MgO·H₂O as support. The gold nanoparticles (AuNPs) are uniformly dispersed on the surface of the Au/MgO catalysts, and have a uniform round shape with a medium size of ~8 nm. On the other hand, the silver nanoparticles (AgNPs) present on the Ag/MgO catalyst have an irregular shape, larger diameters, and less uniform dispersion. The Au–Ag/MgO catalyst contains large Au–Ag bimetallic particles of ~20–30 nm surrounded by small (5 nm) AuNPs. Following the RF-CCVD process and the dissolution of the magnesia support, relative large, few-layer, wrinkled graphene sheets decorated with metal nanoparticles (MeNPs) are observed. Graphene–gold (Gr–Au) and graphene–silver (Gr–Ag) composites had 4–7 graphitic layers with a relatively large area and similar crystallinity for samples prepared in similar experimental conditions. Graphene–gold–silver composites (Gr–Au–Ag) presented graphitic rectangles with round, bent edges, higher crystallinity, and a higher number of layers (8–14). The MeNPs are encased in the graphitic layers of all the different samples. Their size, shape, and distribution depend on the nature of the catalyst. The AuNPs were uniformly distributed, had a size of about 15 nm, and a round shape similar to those from Au/MgO catalyst. In Gr–Ag, the AgNPs have a round shape, very different from that of the Ag/MgO catalyst, large size distribution and are not uniformly distributed on the surface. Agglomerations of AgNPs together with large areas of pristine few-layer graphene were observed. In Gr–Au–Ag composites, almost exclusively large bimetallic particles of about 25–30 nm, situated at the edge of graphene rectangles have been found.     

Ultrasmall dopamine-coated nanogolds: preparation,characteristics, and CT imaging

ABSTRACT

Water-dispersible ultrasmall nanogolds (WDU AuNPs) and their dopamine-coated nanogolds (WDU AuNPs@DPAs) were prepared by a reduction method with sodium borohydride as a reducing agent and a stabilised agent of 2-mercaptosuccinic acid in aqueous solution. The effects of these nanoparticles on computed tomography (CT) imaging were evaluated. The size distributions and Zeta potential of the nanoparticles were measured with a Malvern size analyser, and nanoparticle morphology was observed by transmission electron microscopy. These characteristics were confirmed by Fourier transform spectroscopy and ultraviolet/visible spectra. It was found that WDU AuNPs@DPAs were 5.4 nm in size with clear core–shell structure. The 3-(4, 5-Dimethyl-2-thiazolyl)-2, 5-diphenyltetrazolium bromide assay results showed that the WDU AuNPs and WDU AuNPs@DPAs were hypotoxic to different cells. The WDU AuNPs@DPAs showed a much longer circulation time and a larger CT attenuation coefficient than iohexol and could be excreted by the kidney and bladder. These nanoparticles showed considerable potential for future application in CT imaging.     

Facile fabrication of ultrasmall and uniform copper nanoparticles

Ultrasmall and uniform copper nanoparticles were synthesized through a trace-level ethylenediaminetetraacetic acid (EDTA)-assisted wet chemical route in which Cu(OH)₂ colloid, KBH₄ and polyvinyl pyrrolidone (PVP) were used as the Cu source, the reducing agent, and the protective agents, respectively. The copper nanoparticles exhibit a spherical morphology with a narrow size distribution, a uniform shape, and the average diameter of ca. 4 nm. The presence of trace EDTA is indispensable for the preparation of ultrasmall and uniform copper nanoparticles. EDTA concentration directly influences the copper nanoparticle size and uniformity. As EDTA concentration decreases, the size of the copper nanoparticles decreases, whereas the uniformity increases. The possible formation mechanism of ultrasmall and uniform copper nanoparticles was determined according to experimental results.     

Three-dimensional chemical imaging of embedded nanoparticles using atom probe tomography

Analysis of nanoparticles is often challenging especially when they are embedded in a matrix. Hence, we have used laser-assisted atom probe tomography (APT) to analyze the Au nanoclusters synthesized in situ using ion-beam implantation in a single crystal MgO matrix. APT analysis along with scanning transmission electron microscopy and energy dispersive spectroscopy (STEM-EDX) indicated that the nanoparticles have an average size ~8-12 nm. While it is difficult to analyze the composition of individual nanoparticles using STEM, APT analysis can give three-dimensional compositions of the same. It was shown that the maximum Au concentration in the nanoparticles increases with increasing particle size, with a maximum Au concentration of up to 50%.     

Synthesis, characterization and electrocatalytic activity of fused gold nanoparticles

This paper describes the synthesis of fused spherical gold nanoparticles (AuNPs) and their electrocatalytic activity towards the oxidation of hydroxylamine (HA). Fused AuNPs were prepared by one-pot synthesis using 2-mercapto-4-methyl-5-thiazoleacetic acid (TAA) as a stabilizing agent and sodium borohydride (NaBH4) as a reducing agent. The HR-TEM images showed that two individual AuNP were joined via on its surface with a size range of approximately 7 nm and a length of approximately 15 nm diameter. The pH studies showed that the synthesized fused AuNPs was stable at pH > 8. This indicated that the carboxylate ion present on the TAA molecule stabilized the AuNPs from aggregation. Further, the fused AuNPs were utilized for the electrocatalytic oxidation of hydroxylamine (HA) after immobilized them on (3-mercaptopropyl)-trimethoxysilane (MPTS) sol-gel film modified Au electrode. The AuNPs modified electrode showed an excellent electrocatalytic activity towards the oxidation of HA in 0.2 M phosphate buffer solution (pH 7.2) by shifting its oxidation potential to 100 mV less positive and enhancing its oxidation current for more than three times when compared to bare Au electrode. Further, it was found that the fused AuNPs modified electrode showed greater electrocatalytic activity towards HA than the spherical AuNPs modified electrodes.     

Nanosphere molecularly imprinted polymers doped with gold nanoparticles for high selectivity molecular sensors

We report the first attempt of using molecularly imprinted polymers (MIPs) in the shape of nanoparticles that were doped with gold nanoparticles (AuNPs) for surface enhanced Raman scattering (SERS)-based sensing of molecular species.Specifically,AuNPs doped molecularly imprinted nano-spheres (AuNPs@nanoMIPs) were synthesized by one-pot precipitation polymerization using Sudan Ⅳ as the template for the SERS sensing.The AuNPs@nanoMIPs were characterized by various modes of scanning transmission electron microscopy (STEM) that showed the exact location of the AuNPs inside the MIP particles.The effects of Au concentration and solution stirring on the shape and the polydispersity of the particles were studied.Significant enhancement of the Raman signals was observed only when the MIP particles were doped with the AuNPs.The SERS signal improved significantly with increase in the Au concentration inside the AuNPs@nanoMIPs.Selectivity measurements of the Sudan Ⅳ imprinted AuNPs@nanoMIPs carried out with different Sudan derivatives showed high selectivity of the AuNPs-doped MIP particles.     

Polydisperse composition of mixed monolayer-protected, spin-labeled Au nanoparticles

Using EPR spectroscopy and spin-labeled ligands, we have studied product distribution in the ligand exchange reactions of Au nanoparticles. When the incoming ligand was used in excess, the exchanged nanoparticles had uniform composition of the organic shell. Preparative GPC was employed to fractionate these materials according to the diameter of the Au core, as confirmed by TEM, UV, and EPR measurements. When the exchange reaction was carried out with less than a stoichiometric amount of the incoming ligand, nanoparticles with polydisperse composition of the organic shell were formed. This was established by the EPR analysis of the exchange reaction mixtures following their GPC fractionation. The GPC separation of these mixtures is controlled by both Au core size and shell composition.     

Comparative cytotoxicity evaluation of different size gold nanoparticles in human dermal fibroblasts

The aim of this work was to compare the effects of three commercially available gold nanoparticles (AuNPs) of different sizes (30, 50 and 90 nm) on the viability of normal human dermal fibroblasts (NHDF). In addition, we evaluated protective effect of N-Acetyl-L-cysteine (NAC), total glutathione content (GSH/GSSG), superoxide dismutase (SOD) activity and reactive oxygen species (ROS) production to investigate if oxidative stress was involved in the cytotoxic response of these AuNPs. Although AuNP-induced cytotoxicity was dose and time dependent, nanoparticle size slightly influenced the cytotoxic response of AuNPs assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and lactate dehydrogenase. Regarding oxidative parameters, NAC produced no significant protection of NHDF cells against treatment with any of the three AuNPs. Independently on nanoparticle size, GSH/GSSG content was drastically depleted after 24 h of incubation with the three AuNPs (less than 15% in all cases), while no statistically significant changes on SOD activity were reported (～90% of activity). The three AuNPs also caused a notable increase in the ROS production of NHDF cells. In conclusion, our data suggest that AuNP-induced cytotoxicity in NHDF is mediated by oxidative stress and it is independent of nanoparticle size.     

Gold Nanoparticles Capped with Polyethyleneimine for Enhanced siRNA Delivery

An efficient and safe delivery system for small interfering RNA (siRNA) is required for clinical application of RNA interfering therapeutics. Polyethyleneimine (PEI)‐capped gold nanoparticles (AuNPs) are successfully manufactured using PEI as the reductant and stabilizer, which bind siRNA at an appropriate weight ratio by electrostatic interaction and result in well‐dispersed nanoparticles with uniform structure and narrow size distribution. With siRNA binding, PEI‐capped AuNPs induce more significant and enhanced reduction in targeted green fluorescent protein expression in MDA‐MB‐435s cells, though more internalized PEI/siRNA complexes in cells are evidenced by confocal laser scanning microscopy observation and fluorescence‐activated cell sorting analyses. PEI‐capped AuNPs/siRNA targeting endogenous cell‐cycle kinase, an oncogene polo‐like kinase 1 (PLK1), display significant gene expression knockdown and induce enhanced cell apoptosis, whereas it is not obvious when the cells are treated with PLK1 siRNA using PEI as the carrier. Without exhibiting cellular toxicity, PEI‐capped AuNPs appear to be suitable as a potential carrier for intracellular siRNA delivery.     

Ultrafast Laser Manufacture of Stable,Efficient Ultrafine Noble Metal Catalysts Mediated with MOF Derived High Density Defective Metal Oxides

Supported metal nanoparticles (MNPs) undergo severe aggregation, especially when the interaction between MNPs and their supports are limited and weak where their performance deteriorates dramatically. This becomes more severe when catalysts are operated under high temperature. Here, it is reported that MNPs including Pt, Au, Rh, and Ru, with sub‐2 nm size can be stabilized on densely packed defective CeO₂ nanoparticles with sub‐5 nm size via strong coupling by direct laser conversion of corresponding metal ions encapsulated cerous metal–organic frameworks (Ce‐MOFs). Ce‐MOF serves as an ideal dispersion precursor to uniformly encapsulate noble metal ions in their orderly arranged pores. Ultrafast laser vaporization and cooling forms uniform, ultrasmall, well‐mixed, and exceptionally dense nanoparticles of metal and metal oxide concurrently. The laser‐induced ultrafast reaction (within tens of nanoseconds) facilitates the precipitation of CeO₂ nanoparticles with abundant surficial defects. Due to the well‐mixed ultrasmall Pt and CeO₂ components with strong coupling, this catalyst exhibits exceptionally high stability and activity both at low and high temperatures (170–1100 °C) for CO oxidation in long‐term operation, significantly exceeding catalysts prepared by traditional methods. The scalable feature of laser and huge MOF family make it a versatile method for the production of MNP‐based nanocomposites in wide applications.     

Large-area silicon nanowires from silicon monoxide for solar cell applications

Large-area upstanding silicon nanowires (SiNWs) were synthesized by hot-filament chemical vapor deposition (HFCVD) using silicon monoxide (SiO) powder as Si source under high vacuum (1.2 x 10(-5) Torr). Gold nanoparticles (AuNPs) were employed as catalyst, which were formed on Si substrate by in-situ reduction of gold chloride (AuCl3). The size and distribution of the Au nanoparticles can be easily controlled through chemical reaction conditions. Consequently, the diameter, length and density of SiNWs could be varied in certain range. The SiNWs obtained are single crystalline with growth directions predominantly along [01-1]. Silicon nanowires in large-scale and diameter less than 10 nm can be grown on different Si substrates with this method. Organic inorganic hybrid solar cells based on SiNWs arrays have been demonstrated.     

Size dependence electrocatalytic activity of gold nanoparticles decorated reduced graphene oxide for hydrogen evolution reaction

It is promising for AuNPs/RGO composites to be exploited for hydrogen evolution reaction (HER), due to the collaborative effects between the electrocatalytic Au nanoparticles (AuNPs) and conductive reduced graphene oxide (RGO). In this work, we used a simple way to decorate AuNPs onto the RGO surface by one pot in situ reduction both HAuCl₄ and GO, for which the controlled average size of AuNPs (2.7, 11.5 and 45.7 nm) is adjusting with the mass ratio of HAuCl₄ and GO. The obtained materials, AuNPs/RGO composites, show excellent electrocatalytic activity for the HER that critical dependence on the particle size of AuNPs. The results show that AuNPs/RGO with AuNPs size of 11.5 nm exhibits superior electrochemical activity: low onset potential of 0.029 V versus the reversible hydrogen electrode as well as a small Tafel slope of 86 mV per decade.     

复合纳米金膜的制备及其光学性质

本文利用化学还原法制备了不同尺寸的金纳米颗粒,并利用离子自组装多层技术在玻璃基底上沉积了基于金纳米颗粒的复合纳米金膜,研究了颗粒尺寸和成膜厚度对复合金膜光学性质的影响。不同比例的柠檬酸钠与氯金酸产生的金纳米颗粒溶液的紫外-可见光谱随着金颗粒直径增大而红移展宽。适量比例的柠檬酸钠与氯金酸能够产生平均直径为14±1.2nm且尺寸分布均匀的金纳米球;其溶液在518nm处有一特征吸收峰。不同大小的金纳米颗粒形成的薄膜的紫外-可见光谱形状不同,局域表面等离子体共振峰的位置随着颗粒直径的减小而向短波方向迁移。薄膜的沉积层数越多,薄膜表面的颗粒分布越均匀,局域表面等离子体峰的峰值变化也将减小。本工作证实了利用离子自组装多层技术能够快速、简易、低成本地在玻璃基底上沉积具有局域表面等离子体共振的复合纳米金膜。     

Biostabilised icosahedral gold nanoparticles: synthesis,cyclic voltammetric studies and catalytic activity towards 4-nitrophenol reduction

A green and cost-effective biosynthetic approach for the preparation of icosahedral gold nanoparticles (AuNPs) using an aqueous leaf extract of Polygonum minus as reducing and stabilising factor is described. The reduction of Au³⁺ ions to elemental Au rapidly occurred and is completed within 20 minutes at room temperature. The size of the nanoparticles is highly sensitive to the AuCl₄^?/leaf extract concentration ratio and pH. Transmission electron microscopy and X-ray diffraction data indicated that the nanoparticles were in a crystalline shape (face-centred cubic), mostly icosahedral and nearly monodispersed with an average size of 23 nm. Cyclic voltammetric studies suggested that flavonoids, such as quercetin and myricetin present in the leaf extract had a tendency to donate electrons to Au³⁺ ions and the formation of elemental Au was possible due to the transfer of electrons from these flavonoids to Au³⁺ ions. Infrared absorption of the AuNPs and the leaf extract revealed that the oxidised (quinone) form of quercetin and myricetin were presumably the main stabilising agents in the formation of stable nanoparticles. The present biosynthesis of AuNPs was simple, rapid, cost-effective and environmentally friendly. The newly prepared biostabilised icosahedral AuNPs show good catalytic activity in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP).     

Optical and photoluminescence studies of gold nanoparticles embedded ZnO thin films

Gold nanoparticles (AuNPs) embedded ZnO thin films were prepared by sandwiching a thin thermally evaporated Au film between two sputtered ZnO films. The films were characterized by high resolution transmission electron microscopy (HRTEM), glancing angle X-ray diffraction (GXRD), optical absorption and photoluminescence (PL) measurements. GXRD data exhibited peaks which were attributed to the reflections from various ZnO and Au planes. Size dependence of the plasmon absorption was studied by forming nanoparticles with various sizes. Optical absorption spectra showed strong absorption due to localized surface plasmons at about 608, 638 and 676 nm for films having average AuNPs sizes of 27, 40 and 67 nm respectively. AuNPs embedded ZnO film showed a strong reduction in the intensity of photoluminescence, which was prominent in the case of pure ZnO film. The rise in temperature at a single nanoparticle site was calculated to be 22 K for a particle size of 80 nm.     

Size‐Dependent Cellular Uptake of DNA Functionalized Gold Nanoparticles

The extensive use of gold nanoparticles (AuNPs) in nanomedicine, especially for intracellular imaging, photothermal therapy, and drug delivery, has necessitated the study of how functionalized AuNPs engage with living biological interfaces like the mammalian cell. Nanoparticle size, shape, surface charge, and surface functionality can affect the accumulation of functionalized AuNPs in cells. Confocal microscopy, flow cytometry, and inductively coupled plasma mass spectrometry demonstrate that CaSki cells, a human cervical cancer cell line, internalize AuNPs functionalized with hairpin, single stranded, and double stranded DNA differently. Surface charge and DNA conformation are shown to have no effect on the cell‐nanoparticle interaction. CaSki cells accumulate small DNA‐AuNPs in greater quantities than large DNA‐AuNPs, demonstrating that size is the major contributor to cellular uptake properties. These data suggest that DNA‐AuNPs can be easily tailored through modulation of size to design functional AuNPs with optimal cellular uptake properties and enhanced performance in nanomedicine applications.