Small Gold Research Articles

Cryo-electron tomographic investigation of native hippocampal glutamatergic synapses

Chemical synapses are the major sites of communication between neurons in the nervous system and mediate either excitatory or inhibitory signaling. At excitatory synapses, glutamate is the primary neurotransmitter and upon release from presynaptic vesicles, is detected by postsynaptic glutamate receptors, which include ionotropic AMPA and NMDA receptors. Here, we have developed methods to identify glutamatergic synapses in brain tissue slices, label AMPA receptors with small gold nanoparticles (AuNPs), and prepare lamella for cryo-electron tomography studies. The targeted imaging of glutamatergic synapses in the lamella is facilitated by fluorescent pre- and postsynaptic signatures, and the subsequent tomograms allow for the identification of key features of chemical synapses, including synaptic vesicles, the synaptic cleft, and AuNP-labeled AMPA receptors. These methods pave the way for imaging brain regions at high resolution, using unstained, unfixed samples preserved under near-native conditions.

Cryo-electron tomographic investigation of native hippocampal glutamatergic synapses.

Chemical synapses are the major sites of communication between neurons in the nervous system and mediate either excitatory or inhibitory signaling. At excitatory synapses, glutamate is the primary neurotransmitter and upon release from presynaptic vesicles, is detected by postsynaptic glutamate receptors, which include ionotropic AMPA and NMDA receptors. Here, we have developed methods to identify glutamatergic synapses in brain tissue slices, label AMPA receptors with small gold nanoparticles (AuNPs), and prepare lamella for cryo-electron tomography studies. The targeted imaging of glutamatergic synapses in the lamella is facilitated by fluorescent pre- and postsynaptic signatures, and the subsequent tomograms allow for the identification of key features of chemical synapses, including synaptic vesicles, the synaptic cleft, and AuNP-labeled AMPA receptors. These methods pave the way for imaging brain regions at high resolution, using unstained, unfixed samples preserved under near-native conditions.

Small gold nanoparticles for tandem cyclization/reduction and cyclization/hydroalkoxylation reactions

With peculiar structural features at the surface of small metal nanoparticles, some discrete sites can display catalytic behaviour similar to what could be observed with mononuclear metal catalysts in solution. We have studied the transfer of two catalytic tandem reactions from homogeneous to heterogeneous conditions. Tandem cyclisation/reduction of ortho-alkynyl benzaldehyde derivatives was successfully achieved with Au nanoparticles over TiO2 (Au NPs/TiO2) in the presence of Hantzsch ester with 45-98% yields for 15 examples (average yield: 70.4%). Similarly, tandem cyclisation/hydroalkoxylation of ortho-alkynyl benzaldehyde derivatives was successfully achieved with Au NPs/TiO2 in methanol or other alcohols with 62-96% yields for 17 examples (average yield: 84.9%). The application potential of this catalytic system was demonstrated with the total synthesis of a bioactive isochromene derivative featuring one of the developed reactions as the key step and the implementation of the tandem cyclisation/hydroalkoxylation in a continuous flow reactor, scaling up the reaction by a factor of 10 without loss of efficiency.

NIR-II scattering gold superclusters for intravascular optical coherence tomography molecular imaging.

Currently, intravascular optical coherence tomography (IV-OCT) is limited to anatomical imaging, providing structural information about atherosclerotic plaque morphology, thrombus and dissection. Earlier detection and risk stratification would be possible through molecular characterization of endothelium but necessitates a purpose-engineered IV-OCT contrast agent. Here we developed gold superclusters (AuSCs) tailored to clinical instrumentation and integrated into clinically relevant workflows. AuSCs are aqueously dispersible clusters of closely packed small gold nanoparticles, affording plasmon hybridization to maximize light scattering at the IV-OCT laser line (~1,350 nm). A polymer coating fosters AuSC uniformity and provides a functionalizable handle, which we targeted to intravascular P-selectin, an early vascular endothelial marker of inflammation. In a rat model of intravascular inflammation, P-selectin-targeted AuSC facilitated IV-OCT molecular imaging, where the strength of the signal correlates with the severity of vascular inflammation.

Evaluating Policy and Legal Challenges in the Legalisation of Artisanal Small Scale Gold Mining in West Kalimantan

Evaluating Policy and Legal Challenges in the Legalisation of Artisanal Small Scale Gold Mining in West Kalimantan

Polyvinyl alcohol assisted citrate based reduction of gold(III) ions: Theoretical design and experimental study on green synthesis of spherical and biocompatible gold nanoparticles

In this study, we demonstrate the synthesis of small gold nanoparticles (typically 8-10 nm) through a green synthesis approach. This method involves utilizing chloroauric acid as the gold precursor, trisodium citrate as a mild reducing and co-capping agent, and polyvinyl alcohol (PVA), as a co-capping and shape-directing agent. This novel synthesis method stands alone as a protocol that involves just mixing the reagents at room temperature and allowing the reaction to proceed at ambient temperature without any disturbance. In the absence of PVA, spherical particles are not formed and the reaction mixture slowly turns black followed by precipitation.The synthesis process was meticulously tracked using time-resolved monitoring of the growth of the localized surface plasmon resonance (LSPR) by UV-vis spectroscopy and transmission electron microscopy. The as-prepared colloidal gold solution was bright red, attributed to the small size (≤ 10 nm) and spherical geometry of nanoparticles. This colloidal solution could be stored indefinitely at room temperature without precipitation or a change in its absorption profile. The nanoparticles remained stable in adverse conditions such as 100 mM NaCl solution, 1×PBS and cell culture medium. Additionally, they could be easily loaded with drugs like doxorubicin by adsorption. The particles were thoroughly characterized using a range of techniques, including UV-vis spectroscopy, attenuated total reflectance Fourier-transform infrared spectroscopy (ATR-FTIR), high-resolution transmission electron microscopy (HRTEM), hyperspectral-enhanced dark field microscopy (HEDFM), dynamic light scattering (DLS), and X-ray photoelectron spectroscopy (XPS). Cell viability tests conducted on 2D cell lines and 3D spheroids revealed negligible toxicity even at high concentrations. Furthermore, we demonstrate that an advanced version of conventional diffusion-limited aggregation (DLA) schemes, which allows individual clusters to move freely within a domain to form larger aggregates, can effectively replicate the intricate interactions between chloroauric acid, trisodium citrate, and PVA, the agents involved in the synthesis of gold nanoparticles.

Cyanide and cyanidation wastes management in gold leaching plants in Siaya County, Kenya.

This study assesses cyanide and cyanidation wastes management practices among small, medium and large-scale gold leaching plants in Siaya County, Kenya. The socio-economic benefits of gold extraction through cyanidation of mercury-contaminated tailings notwithstanding, the study establishes inadequate cyanide and cyanidation wastes management practices which could potentially cause significant environmental and human health impacts. Through structured key-informant interviews with operators from 15 selected gold leaching plants of varying scales of operation, along with field observations, and quantitative analysis utilizing both bivariate and inferential statistical tools, the study reveals inadequacies in cyanide, cyanidation wastewater, and tailings management practices. Key findings highlight widespread contravention of the international cyanide management standards and lack of adoption of advanced cyanidation wastes treatment technologies. Moreover, the study examines Political, Economic, Social, Technological, Environmental, and Legal factors as external factors affecting the management of cyanidation wastes. Consequently, the study recommends adoption of comprehensive cyanide management practices as outlined in the Cyanide Code and technological upgrades to mitigate potential environmental and human health impacts, and enhance regulatory compliance in gold cyanidation. In a nutshell, this study underscores the urgent need for stringent enforcement of environmental and mining industry laws and regulations in order to protect the environment and public health in gold mining regions. These measures are vitally important to ensure responsible mining practices and uphold environmental stewardship while promoting economic growth.

Modelling the anthropogenic Hg pollution fingerprint on the marine fishery production worldwide: A preliminary exposure assessment for people living in countries having different income levels

Mercury is a toxic pollutant that poses risks for the human population, mainly by eating contaminated fish. Mercury is released into the atmosphere from a variety of anthropogenic activities, with levels of emissions and under policy controls that largely vary across the world, leading thus to different relative contributions to the environmental matrices. Establishing the exact sources of this contaminant in the environment is crucial to optimising the policies aimed at mitigating the exposure risks for specific populations or ecosystems. In this study, we modelled, for the first time, the fingerprint of mercury anthropogenic emissions, jointly released by source-sectors (11) and source-regions (13), on the deposition over (19) FAO fishery zones, and on the FAO official fishery productions worldwide over the 2012–2021 decade. Using mercury anthropogenic emissions for 2012 from EDGAR, East Asia and ”Artisanal and Small scale Gold Mining” result the source-region and the source-sector, respectively, that contribute the most to the mercury deposition over all the FAO fishery zones. The only exception applies for the FAO fishery zone 37, the Mediterranean Sea, where the ”Industrial Combustion” from the closest Europe is the pair region-sector whose joint contribution is the greatest. When normalised to the overall fishery production worldwide, representing the global fish consumption, the anthropogenic mercury fingerprint showed a similar general pattern, however with notable differences, amplifying the relative contributions of all source-sectors from East Asia and attenuating the relative contributions of the regions in the Southern Hemisphere. This fingerprint further changes when the fish consumption in countries, classified by the World Bank as having different incomes, is considered. These results demonstrate that the same anthropogenic mercury deposited on any fishery zone actually affects in a different way the different population segments worldwide. This study aims to urge the science community as well as the policy makers to use a measure that better represents the mercury hazard for human health. Further, we hope that this study, using nomenclatures that are largely used on final shelf-product, could increase the people’s awareness regarding the products they consume.

A Comparative Study of the Effect of Oxygen-Containing Functional Groups in GO and rGO Sheets Decorated with Small Gold Nanoparticles on Bioactivities

A Comparative Study of the Effect of Oxygen-Containing Functional Groups in GO and rGO Sheets Decorated with Small Gold Nanoparticles on Bioactivities

Makrofungi Resisten Merkuri (Hg)

This study aims to identify types of macrofungi that are resistant to the presence of Hg in their environment. The method used is survey research by exploring mushrooms in the area around the Small Scale Gold Mining (ASGM). Tambang Sawah Village, Lebong Regency, Bengkulu Data findings were analyzed by descriptive qualitative. The results showed that the types of macrofungi that were able to survive Hg stress were Ganoderma applanatum, Dacryopinax spathularia, Daldinia concentrica, Ganoderma lucidum and Polyporus alveolaris. In conclusion, five types of macrofungi that are adaptive to mercury (Hg) were found. The highest Hg accumulation was found in D. concentrica.

Solvation Properties of Neutral Gold Species in Supercritical Water Studied By THz Spectroscopy.

Supercritical water provides distinctly different solvation properties compared to what is known from liquid water. Despite its prevalence deep in the Earth's crust and its role in chemosynthetic ecosystems in the vicinity of hydrothermal vents, molecular insights into its solvation mechanisms are still very scarce compared to what is known for liquid water. Recently, neutral metal particles have been detected in hydrothermal fluids and proposed to explain the transport of gold species to ore deposits on Earth. Using ab initio molecular dynamics, we elucidate the solvation properties of small gold species at supercritical conditions. The neutral metal clusters themselves contribute enormous THz intensity not because of their intramolecular vibrations, but due to their pronounced electronic polarization coupling to the dynamical supercritical solvent, leading to a continuum absorption up to about 1000 cm-1. On top, long-lived interactions between the gold clusters and solvation water leads at these supercritical conditions to a sharp THz resonance that happens to be close to the one due to H-bonding in liquid water at ambient conditions. The resulting distinct resonances can be used to analyse the solvation properties of neutral metal particles in supercritical aqueous solutions.

FTIR spectroscopy revealed nonplanar conformers, chain order, and packaging density in diOctadecylamine- and octadecylamine-passivated gold nanoparticles

This work reveals that diOctadecylamine (diODA) outperforms its primary amine counterpart ODA in intra- and intermolecular order, forming passivation monolayers on 5 nm small gold nanoparticles. We support this conclusion by meticulously analyzing the differences in the Fourier Transform Infrared (FTIR) spectrum of diODA and ODA molecules in their pure- and coordinated-to-gold-nanoparticle phases. Detailed diODA spectral data are scarce in the literature and are absent for diODA-passivated nanoparticles, whose merits have gone unnoticed. The analysis compares the signatures of defects and all indicators for molecular packing in the ligand. The results align with the High-Resolution Transmission Electron Microscopy (HR-TEM) based analysis. We observe unexpectedly that pure diODA molecules are not prone to form trans-gauche (TG) [CH3-CH2-gauche] end-conformation. At the same time, an intensive absorption structure at the relevant TG position around 760 cm−1 indicates its presence in pure ODA. The spectrum of pure ODA indicates higher energy of the internal kink defects in the vicinity of 1306 cm−1 than pure diODA. In the coordinated phase, both molecules reduce their initial energy. However, the observed better-pronounced red shift of the structures reveals a crystal-like chain arrangement for diODA. Consequently, the HR-TEM images reveal a spontaneous formation of 2D arrangement only for diODA passivated nanoparticles having nearly twice as large gold core separation as the one provided by ODA molecules. The present analysis can be used as a preliminary test in demanding applications where tightly packed coatings of nanoparticles with impenetrable organic passivation are essential.

Controlled Biocatalytic Synthesis of a Metal Nanoparticle-Enzyme Hybrid: Demonstration for Catalytic H2-driven NADH Recycling.

Here we demonstrate the preparation of enzyme-metal biohybrids of NAD+ reductase with biocatalytically-synthesised small gold nanoparticles (NPs, <10 nm) and core-shell gold-platinum NPs for tandem catalysis. Despite the variety of methods available for NP synthesis, there remains a need for more sustainable strategies which also give precise control over the shape and size of the metal NPs for applications in catalysis, biomedical devices, and electronics. We demonstrate facile biosynthesis of spherical, highly uniform, gold NPs under mild conditions using an isolated enzyme moiety, an NAD+ reductase, to reduce metal salts while oxidising a nicotinamide-containing cofactor. By subsequently introducing platinum salts, we show that core-shell Au@Pt NPs can then be formed. Catalytic function of these enzyme-Au@Pt NP hybrids was demonstrated for H2-driven NADH recycling to support enantioselective ketone reduction by an NADH-dependent alcohol dehydrogenase.

Design and Implementation of Dongba Character Font Style Transfer Model Based on AFGAN.

Dongba characters are ancient ideographic scripts with abstract expressions that differ greatly from modern Chinese characters; directly applying existing methods cannot achieve the font style transfer of Dongba characters. This paper proposes an Attention-based Font style transfer Generative Adversarial Network (AFGAN) method. Based on the characteristics of Dongba character images, two core modules are set up in the proposed AFGAN, namely void constraint and font stroke constraint. In addition, in order to enhance the feature learning ability of the network and improve the style transfer effect, the Convolutional Block Attention Module (CBAM) mechanism is added in the down-sampling stage to help the network better adapt to input font images with different styles. The quantitative and qualitative analyses of the generated font and the real font were conducted by consulting with professional artists based on the newly built small seal script, slender gold script, and Dongba character dataset, and the styles of the small seal script and slender gold script were transferred to Dongba characters. The results indicate that the proposed AFGAN method has advantages in evaluation indexes and visual quality compared to existing networks. At the same time, this method can effectively learn the style features of small seal script and slender gold script, and transfer them to Dongba characters, indicating the effectiveness of this method.

Highly Biocompatible Hemoglobin-Stabilized Gold Nanoparticles for an Enhanced Catalytic Reduction of 4-Nitrophenol

4-nitrophenol (4-NP) is a frequently encountered toxic phenolic organic pollutant in water. It is important to develop a simple method to treat 4-NP. Small and monodispersed gold nanoparticles often have good catalytic performance of 4-NP. Hemoglobin (Hb) is a kind of common and important protein in organisms. Herein, highly biocompatible bovine hemoglobin-stabilized gold nanoparticles (Aun-Hb NPs) were synthesized using hemoglobin as a biological template. Then, the size, zeta potential, and composition of Aun-Hb NPs were investigated by transmission electron microscopy, dynamic light scattering, and X-ray photoelectron spectroscopy. The Aun-Hb NPs with small gold nanoparticles of about 1.4–2.4 nm had good catalytic capabilities in reducing 4-NP to form 4-aminophenol. Au20-Hb NPs demonstrated superior catalytic efficiency in the reduction of 4-NP when compared to other nanoparticles. Moreover, as-synthesized Au20-Hb NPs exhibited excellent biocompatibility through the MTT experiment. The method of preparation of gold nanoparticles offers one way to prepare metal nanoparticles for good potential catalytic applications of gold nanoparticles.

Rapid detection of melamine by DNA Walker mediated SERS sensing technique based on signal amplification function.

A new method is proposed for detecting typical melamine dopants in food using surface-enhanced Raman scattering (SERS) biosensing technology. Melamine specific aptamer was used as the identification probe, and gold magnets (AuNPs@MNPs) and small gold nanoparticles (AuNPs@MBA) were used as the basis for Raman detection. The Raman signal of the detection system can directly detect melamine quantitatively. Under optimized conditions, the detection of melamine was carried out in the low concentration range of 0.001-500mg/kg, the enhancement factor (EF) was 2.3 × 107, and the detection limit was 0.001mg/kg. The method is sensitive and rapid, and can be used for the rapid detection of melamine in the field environment.

Adsorption of O2 on the Preferred -O-Au Sites of Small Gold Oxide Clusters: Charge-dependent Interaction and Activation.

Decades of research have illuminated the significant roles of gold/gold oxide clusters in small molecule catalytic oxidation. However, many fundamental questions, such as the actual sites to adsorb and activate O2 and the impact of charge, remain unanswered. Here, we have utilized an improved genetic algorithm program coupled with the DFT method to systematically search for the structures of Au1-5Ox-/+/0 (x = 1-4) and calculated binding interactions between Au1-5Ox-/+/0 (x = 1-2) and O2, aiming to determine the active sites and to elucidate the impact of different charge states in gold oxide systems. The results revealed that the reactivity of all three kinds of small gold oxide clusters toward O2 is strongly site-dependent, with clusters featuring an -O-Au site exhibiting a preference for adsorption. The charges on small gold oxide clusters significantly impact the interaction strength and the activation degree of adsorbed O2: in the case of anionic cluster, the interaction between O2 and the -O-Au sites leads to a chemical reaction involving electron transfer, thereby significantly activating O2; in neutral and cationic clusters, the adsorption of O2 on their -O-Au sites can be viewed as an electrostatic interaction. Pointedly, for cationic clusters, the highly concentrated positive charge on the Au atom of the -O-Au sites can strongly adsorb but hardly activate the adsorbed O2. These results have certain reference points for understanding the gold oxide interfaces and the improved catalytic oxidation performance of gold-based systems in the presence of atomic oxygen species.

Facile construction of gold- and BODIPY-coordinated liposomal nanocomplexes for enhanced photothermal therapy of cancer

Photothermal therapy (PTT) has attracted extensive attention in cancer treatment because of its advantages of non-invasive and few side effects. Gold nanoparticles and boron-fluorine-dipyrrole (BODIPY) dye have been used as photothermal agents (PTAs), but they have problems such as easy aggregation, poor water solubility and low photothermal conversion efficiency. In this work, we used conventional liposomes for in situ generation of small gold nanoparticles and sequentially loading BODIPY to overcome the drawbacks of the two PTAs and simultaneously realize enhanced PTT. Gold- and BODIPY-coordinated liposomal nanocomplexes LAB with small gold nanoparticles adsorbed on the surface and BODIPY entrapped inside showed uniform size of about 100 nm with good stability. LAB demonstrated laser-responsive drug release property, good cellular uptake efficiency and tumor accumulation ability. After laser irradiation, LAB can exert enhanced PTT in cancer cell lines by reducing mitochondrial membrane potential and increase intracellular reactive oxygen species level to promote cell apoptosis. In tumor-bearing mice, LAB showed fantastic tumor inhibition effect with good biosafety. This work provides a convenient method to develop PTA combinations for enhanced PTT, which could lay the foundation for the green construction of new PTAs for PTT by employing clinically used formulations and PTAs.

Role of Gold Nanoparticles in Drug Delivery

Recent developments in nanotechnology offer a multitude of approaches for investigating and tracking diverse biological and medical processes at the nanoscale. Nanoparticles can deliver medications directly to cancer cells, aiding in the diagnosis and treatment of diseases like cancer. Gold nanoparticles (AuNPs) are incredibly small gold particles, usually fewer than 100 nanometers in size. They are measured in nanometers. AuNPs are one type of nanoparticle that has shown promise as a medication delivery platform. Their outstanding stability, adjustable chemical and physical characteristics, and biocompatibility make them incredibly beneficial for drug delivery applications. The physical and chemical features of AuNPs' natural characteristics were studied. Localized surface plasmon resonance (LSPR), radioactivity, and a high X-ray absorption coefficient are among the physical characteristics of AuNPs that are commonly used in diagnosis and treatment. Compared to many other nanoparticles, AuNPs can create stable chemical interactions with groups that contain S and N. As a result, AuNPs can bind to a broad range of chemical ligands or polymers used for particular purposes. According to recent research, AuNPs can be easily modified to allow the delivery of pharmaceutical drugs directly to the target tissue. This article provides a brief overview of the more effective synthesis method for AuNPs and how they can be utilized as drug carriers to improve precision medicine.

Ultra-stable and highly reactive colloidal gold nanoparticle catalysts protected using multi-dentate metal oxide nanoclusters

Owing to their remarkable properties, gold nanoparticles are applied in diverse fields, including catalysis, electronics, energy conversion and sensors. However, for catalytic applications of colloidal gold nanoparticles, the trade-off between their reactivity and stability is a significant concern. Here we report a universal approach for preparing stable and reactive colloidal small (~3 nm) gold nanoparticles by using multi-dentate polyoxometalates as protecting agents in non-polar solvents. These nanoparticles exhibit exceptional stability even under conditions of high concentration, long-term storage, heating and addition of bases. Moreover, they display excellent catalytic performance in various oxidation reactions of organic substrates using molecular oxygen as the sole oxidant. Our findings highlight the ability of inorganic multi-dentate ligands with structural stability and robust steric and electronic effects to confer stability and reactivity upon gold nanoparticles. This approach can be extended to prepare metal nanoparticles other than gold, enabling the design of novel nanomaterials with promising applications.