Gold Bulletin最新文献

Green synthesis of metal nanoparticles using plant-derived extracts has emerged as a sustainable alternative to conventional chemical and physical methods. In this work, silver nanoparticles (AgNPs) were synthesized using aqueous leaf extract of Catha edulis as a reducing and stabilizing agent. The formation of AgNPs was confirmed by the characteristic color change of the reaction mixture and the appearance of a distinct surface plasmon resonance (SPR) band at 416 nm in the UV–Vis spectrum. Structural characterization by X-ray diffraction revealed diffraction peaks at 2θ values of 38.23°, 44.34°, 64.52°, and 77.39°, corresponding to the (111), (200), (220), and (311) planes of face-centered cubic silver, confirming crystallinity. Fourier transform infrared analysis indicated the involvement of phytochemicals, including flavonoids, phenolics, alkaloids, and tannins, in nanoparticle formation and stabilization. The biosynthesized AgNPs exhibited measurable antibacterial activity against K. pneumoniae and S. pyogenes, producing a zone of inhibition (ZOI) of 21.20 ± 0.78 mm and 18.63 ± 0.53 mm respectively. These findings highlight the potential of Catha edulis extract for the eco-friendly synthesis of functional AgNPs with promising biomedical applications.

Nanoparticles are increasingly being employed in a variety of industrial and environmental applications. In this study, we aimed to develop a sustainable method for synthesizing silver nanoparticles and to evaluate their potential as algal growth inhibitors. A seedless protocol was established using ascorbic acid and polyvinylpyrrolidone (PVP) to obtain spherical silver nanoparticles, thereby avoiding the use of strong reducing agents. The nanoparticles were characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM), and IR spectroscopy. Since microalgae and other marine organisms often grow on the surfaces of boats, ships, and other human-made devices in aquatic environments, antifouling products are necessary to prevent unwanted fouling. The algal growth inhibition capacity of the synthesized silver nanoparticles was assessed using two marine diatoms Cylindrotheca Closterium and Skeletonema marinoi. The results revealed a marked inhibitory effect on algal proliferation in treated samples compared to controls. Overall, this study demonstrates the effectiveness of the proposed synthetic method and paves the way for the use of these silver nanoparticles as a tool for controlling microalgal growth.

Artisanal and Small-scale Gold Mining (ASGM) operations increasingly adopt mechanized comminution, assuming it universally improves gold recovery. This case study challenges that generalized approach through a comparative field performance evaluation of two gravity recovery circuits processing saprolite ore in Suriname: a traditional direct sluicing system (IST) and a mechanized hammer mill-centrifuge system (HS). Operational parameters and fractional gold deportment were evaluated using a reconstituted head grade methodology to mitigate the fundamental sampling error inherent to high-nugget deposits. Feed characterization revealed that approximately 80% of the gold is in the coarse fractions (> 100 μm), indicating natural amenability to simple gravity recovery. Results demonstrate both circuits severely underperformed due to operational misapplication. The IST circuit operated with extreme slurry viscosity (> 30% solids), causing hydrodynamic carry-over. Conversely, the HS circuit suffered from mechanical overloading and extreme hydraulic dilution (11–17% solids). Furthermore, deportment data suggests the hammer mill failed to achieve effective liberation, discarding ~ 70% of unrecovered gold in mid-size fractions (+ 250–1000 μm) and potentially flattening malleable nuggets. These combined inefficiencies project an estimated annual unrealized value of US$6.9 million (IST) and US$3.8 million (HS) under 2019 pricing. The findings strongly indicate that for gold in the coarse fraction of a saprolitic ore, the routine application of hammer mills may represent a metallurgical mismatch. Implementing strict process control over pulp density and feed rate, alongside proactive on-site ore characterization, are more critical drivers of operational profitability than deploying complex comminution technology.

Gold nanoparticles (AuNPs) exhibit exceptional physicochemical properties, notably localized surface plasmon resonance (LSPR), enabling diverse applications in biomedicine, molecular imaging (CT/PAI/MRI), photothermal therapy (PTT), and targeted drug delivery. This review systematically examines synthesis strategies, emphasizing pulsed laser ablation in liquid (PLAL) as a surfactant-free, eco-friendly “top-down” method producing pristine 5–50 nm AuNPs via plasma plume confinement and cavitation-induced nucleation. Complementary “bottom-up” green biosynthesis leverages plant/fruit extracts (polyphenols/flavonoids), microorganisms, and fungi (nitrate reductase) to yield biofunctionalized AuNPs (10–80 nm) with inherent stability for theranostics. Comparative analyses highlight PLAL’s superiority in purity/yield compared to chemical methods, while biological methods excel in scalability and multifunctionality. Shape-dependent plasmonic heating: nanorods achieve ΔT = 45–55 °C vs. spheres (25 °C), underpinning PTT efficacy. The review elucidates targeting strategies (passive EPR vs. active ligand-receptor), hybrid imaging, and challenges, including EPR heterogeneity, synthesis reproducibility, and clinical translation. Future directions prioritize fs-PLAL optimization, biohybrid architectures, and multimodal AuNP platforms for precision oncology.

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To address the challenge of in-situ monitoring of melt pool dynamics in laser additive manufacturing (LAM), this work proposes a gas-jet excitation method to probe surface wave behavior in liquid metals. Using an In51Bi32.5Sn16.5 alloy (melting point ≈ 60 °C), controlled airflow was applied across temperatures from 90 °C to 60 °C, and surface ripple evolution was captured via high-speed imaging. Image analysis revealed that both wave velocity and wavelength decrease markedly with cooling: stable concentric ripples form at 70 °C, while coherent waves vanish at 60 °C due to incipient solidification. Numerical simulations qualitatively reproduced the ring-like waves and keyhole-like depressions, showing trend-level consistency with the experimental observations. The findings suggest that gas-jet-excited surface-wave characteristics may provide potential observable signals for characterizing the near-solidification state of liquid metal and may offer a conceptual basis for future melt-pool monitoring methods.

Gold-based materials are widely used in electronics, catalysis, and biomedicine due to their excellent conductivity, chemical stability, and biocompatibility; however, their low strength and poor wear resistance limit structural applications. Microalloying, defined as the addition of trace elements (< 0.5 wt%), offers an effective strategy to overcome these limitations through microstructural control. This review presents a mechanism-oriented analysis of microalloying in gold-based systems, focusing on solid solution strengthening, grain boundary engineering, and precipitation hardening, with emphasis on their coupled, multiscale effects. Representative elements (e.g., Ti, Ce, Ag) are evaluated in terms of strengthening efficiency, ductility balance, and functional contributions, revealing roles governed by precipitation behavior, grain boundary regulation, and electronic structure modulation. The detrimental effects of impurity elements (Pb, Bi, Ge) are also examined from a grain boundary cohesion perspective, highlighting the importance of compositional control. By linking microstructure to properties, this review shows that optimal performance arises from synergy among phase stability, defects, and processing. Emerging strategies, including high-throughput computation, machine learning, and additive manufacturing, enable accelerated alloy design. Future advances will integrate data-driven design with precise microstructural engineering to develop high-performance, multifunctional gold-based materials.

The electronic, optical, and thermoelectric properties of flouro double perovskites (FDPs) Rb₂AuMF₆ (M = Co and Rh) have been investigated using density functional theory and semiclassical Boltzmann transport theory. Enthalpy of formation energy (E_f), cohesive energy, and Goldschmidt tolerance factor (t_f) are calculated to assure the stability of the structure. These materials exhibit band gaps between 1.454 eV and 1.828 eV, placing them within the visible light range and indicating their potential suitability for solar energy harvesting. Dielectric tensor, energy loss absorption, optical conductivity, refraction, and reflection are examples of optical properties that have been researched to look at how incident light interacts with the FDPs under investigation. The calculated bulk moduli are 66.72 GPa (Rb₂AuCoF₆) and 65.38 GPa (Rb₂AuRhF₆), reflecting their mechanical robustness. Optical analyses reveal low reflectivity (0.05–0.08), strong absorption, and high optical conductivity in the visible–UV spectrum, suggesting potential for optoelectronic applications. Additionally, these compounds’ thermoelectric behaviour has been examined to determine viability for thermoelectric applications. Thermoelectric performance is promising, with Seebeck coefficients of ~ 181 µV/K and ZT values of 0.177 (Rb₂AuCoF₆) and 0.138 (Rb₂AuRhF₆), while electrical conductivity (σ/τ) and power factors are also favorable. The assessed values of ZT predict that Rb₂AuCoF₆ is comparatively a promising material for TE applications.

Gold nanoparticles (AuNPs) are widely utilized in colorimetric sensing, leveraging their optical characteristics to identify variables through noticeable color alterations. Polymer (PVP)-functionalized gold nanoparticles were successfully prepared in a single step by the induced plasma-under-liquid process. We will evaluate plasma-liquid method synthesis by GREEnness calculator. The effects of different concentrations of PVP on the synthesis and characteristics of the AuNPs, such as size distributions, hydrodynamic diameters, polydispersity indices (PDI), absorbance intensity, and LSPR, were characterized and investigated. The as-synthesized PVP-AuNPs were characterized by SEM, DLS, and UV–visible spectroscopy. Spherical AuNPs were generated, displaying a maximal absorption peak at around 530–560 nm and a size range of 30–50 nm, which can be adjustable depending on the initial concentration precursor and capping agent used in the synthesis process. Polyvinylpyrrolidone-coated gold nanoparticles (PVP-AuNPs) were employed as a colorimetric probe for the quick, easy, sensitive, and selective measurement of chromium ion (Cr(VI)) contamination in water. In fact, chromium ion (Cr(VI)) caused the colloidal solution’s hue to change from red to blue by forcing PVP-AuNPs to aggregate with PVP on the surface of AuNPs. It was established that size and polydispersity affect the colorimetric properties of functionalized nanoparticles during colorimetric detection of the analyte. Optimizing the experimental parameters (volume/concentration AuNPs, the dependence of limit of quantification (LOQ), limit of detection (LOD) at temperature) revealed a good linear connection between the concentration of chromium ion (Cr(VI)) and the absorption ratio (A₆₉₀/A_530-560) in the range of 0.1–3.0 µM with a detection Limit of 0.072–0.1 µM. The selectivity of the developed colorimetric nanoprobe was evaluated by testing its response to various common heavy metal ions. The analytical GREEnness calculator, a comprehensive assessment approach to this method, uses 12 principles of green analytical chemistry which transformed into a unified 0–1 scale. Potential use of methods in quality control laboratories is valuable for the pharmaceutical sector.

Bacterial infections constitute one of the major health issues for the next decades, and their detection through affordable methods is currently an urgency. Cell surface glycans constitute interesting biomarkers, since they are specific, abundant, and diverse. However, their identification has been commonly based on sophisticated, high-cost techniques, such as mass spectrometry or immunolabeling. We herein propose a surface-enhanced Raman spectroscopy (SERS) approach based on optically active gold nanoparticles targeted to D-mannoside and D-glucoside, two common terminal sugars of bacterial glycans. To do so, nanoparticles were decorated with Concanavalin A through a simple physisorption step before using them to generate Raman signals. The use of the construct with beta-methyl-D-mannoside, a well-known Concanavalin A ligand, was found to generate SERS signals of dose-dependent intensities. Moreover, the application of the functional system with three different bacterial species induced differential SERS profiles that included Raman bands specific to cell surface glycolipids. Transmission electron microscopy analyses of bacterial-nanogold preparations revealed that both cell surface and secreted glycans can be tagged by using the gold-lectin construct. Further research is therefore encouraged to better assess this functional nanotag in microbial detection.