Ultra-small Silver Nanoparticles Research Articles

Conversion of Ultrasmall Glutathione-Coated Silver Nanoparticles during Dispersion in Water into Ultrasmall Silver Sulfide Nanoparticles.

Ultrasmall silver nanoparticles (2 nm) were prepared by reduction with sodium borohydride (NaBH4) and stabilized by the ligand glutathione (a tripeptide: glycine-cysteine-glutamic acid). NMR spectroscopy and optical spectroscopy (UV and fluorescence) revealed that these particles initially consist of silver nanoparticles and fluorescing silver nanoclusters, both stabilized by glutathione. Over time, the silver nanoclusters disappear and only the silver nanoparticles remain. Furthermore, the capping ligand glutathione eliminates hydrogen sulfide (H2S) from the central cysteine and is released from the nanoparticle surface as tripeptide glycine-dehydroalanine-glutamic acid. Hydrogen sulfide reacts with the silver core to form silver sulfide. After four weeks in dispersion at 4 °C, this process is completed. These processes cannot be detected by transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), or differential centrifugal sedimentation (DCS) as these methods cannot resolve the mixture of nanoparticles and nanoclusters or the nature of the nanoparticle core. X-ray photoelectron spectroscopy showed the mostly oxidized state of the silver nanoparticle core, Ag(+I), both in freshly prepared and in aged silver nanoparticles. These results demonstrate that ultrasmall nanoparticles can undergo unnoticed changes that considerably affect their chemical, physical, and biological properties. In particular, freshly prepared ultrasmall silver nanoparticles are much more toxic against cells and bacteria than aged particles because of the presence of the silver clusters.

Facile Synthesis of Ultra-Small Silver Nanoparticles Stabilized on Carbon Nanospheres for the Etherification of Silanes.

The dehydrocoupling reaction between alcohols and hydrosilanes is considered to be one of the most atom-economical ways to produce Si-O coupling compounds because its byproduct is only hydrogen (H2), which make it extremely environmentally friendly. In past decades, various kinds of homogeneous catalysts for the dehydrocoupling of alcohols and hydrosilanes, such as transition metal complexes, alkaline earth metals, alkali metals, and noble metal complexes, have been reported for their good activity and selectivity. Nevertheless, the practical applications of these catalysts still remain unsatisfactory, which is mainly restricted by environmental impact and non-reusability. A facile and recyclable heterogeneous catalyst, ultra-small Ag nanoparticles supported on porous carbon (Ag/C) for the etherification of silanes, has been developed. It has high catalytic activity for the Si-O coupling reaction, and the apparent activation energy of the reaction is about 30 kJ/mol. The ultra-small Ag nanoparticles dispersed in the catalyst through the carrier C have an enrichment effect on all reactants, which makes the reactants reach the adsorption saturation state on the surface of Ag nanoparticles, thus accelerating the coupling reaction process and verifying that the kinetics of the reaction of the catalyst indicate a zero-grade reaction.

Synthesis and Antibacterial Activity of Ultrasmall Silver Nanoparticles by Pulsed Laser Ablation in Deionized Water

Background: The main objective of this work is the synthesis and evaluation of silver nanoparticles (Ag NPs) by using pulsed laser ablation of a silver (Ag) target in deionized water and examining their antibacterial activity. Methods: Colloidal solutions of silver nanoparticles were prepared with different pulsed laser energies (620, 880, and 1000) mJ of wavelength 1064 nm and frequency 10 Hz. To determine their structure, optical, morphology, elemental composition, and infrared spectra, the synthesized Ag NPs were characterized using various high-throughput analytical techniques such as (UVVis) spectroscopy, transmission electron microgram (TEM), electron dispersive X-ray spectroscopy (EDX), Fourier transform infrared (FTIR) spectra, and Zeta potential. Results: The results show that the properties of synthesized Ag NPs depend much more on the laser energy. The laser energy can be used to control the properties of the prepared nanoparticles. Uniform distributions of spherical ultrasmall Ag NPs with an average size of (3) nm were obtained suspended in deionized water, which is the most effective size for antibacterial activity. However, the result indicated that the ablated Ag NPs were stable for 4 months in deionized water. The antibacterial activity of the colloidal solution of synthesized Ag NPs against Gramnegative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) bacteria was then examined using the agar-well diffusion method. Conclusion: It was found that the prepared nanoparticles exhibited strong activity against E. coli and S. aureus bacteria growth. The average zones of inhibition of Ag NPs were found to be about (26) mm for E. coli and (32) mm for S. aureus bacteria.

Kaolinite-mediated synthesis of ultra-small silver nanoparticles with high antimicrobial activity.

Ultra-small Ag nanoparticles (<5 nm) loaded on a kaolinite surface were successfully prepared in large batches by a dry-process, displaying excellent broad-spectrum antimicrobial ability and size-dependent activity. This Ag-loaded kaolinite (Ag@AT/K) inhibited the growth of pathogenic bacteria and accelerated wound healing in in vivo experiments on MRSA-infected wounds. This work provides a new strategy for the preparation of mineral-based nanoscale antibacterial materials.

Alginic acid-functionalized silver nanoparticles: A rapid monitoring tool for detecting the technology-critical element tellurium

The increasing global demand for tellurium, driven by its critical role in alloys, photovoltaic devices, and electronics, has raised concerns about its environmental pollution and neurotoxicity. In response, the potential of alginic acid (AA), a renewable, low-cost, and sustainable biopolymer, was explored for the biosynthesis of ultra-small silver nanoparticles (AgNPs) and their application in the detection of tellurium (Te(IV)). The effect of key synthesis parameters on desired physicochemical properties and yield of AgNPs was established to ensure high specificity and sensitivity towards Te(IV). The purified AgNPs with AA surface ligands were utilized to demonstrate a ratiometric absorbance sensor that exhibits excellent linearity and nanomolar-level affinity. This approach achieved a high correlation coefficient of ∼ 0.982, with a low detection limit of about 22 nM. Further investigations into the effect of pH, ionic strength, and organic molecules were conducted to elucidate detection performance and molecular understanding. The detection mechanism relies on the coordination between Te(IV) ions and the carboxylate groups of AA, which initiates aggregation-induced plasmon coupling in adjacent AgNPs. The capability of this analytical method to monitor Te(IV) in real-world water samples features its rapidity, user-friendliness, and suitability for point-of-care monitoring, making it a promising alternative to more complex techniques.

Clearing intratumoral bacteria to augment tumor-therapeutic response by engineering antimicrobial dendritic mesoporous silica nanomedicine

As an important component of the tumor microenvironment, the intratumoral bacteria can significantly reduce the chemotherapeutic response, in which Fusobacterium nucleatum has been established as the representative intratumoral bacteria in colorectal cancer, promoting chemotherapy resistance by activating autophagy pathways. Herein, the concept of antibacterial-augmented antitumor nanomedicine for pathogen-related cancer therapy was elaborated by designing antibacterial-antineoplastic nanoagents that modulate intratumoral bacteria to augment anticancer efficiency. A generic coordination-redox strategy was used for homogeneous in situ growth of antibacterial ultrasmall silver nanoparticles into the dendritic mesoporous silica nanoparticles, which were further loaded with chemotherapeutic drugs. The antibacterial-antineoplastic agents exhibited excellent antitumor efficacy by scavenging Fusobacterium nucleatum to modulate autophagy, thereby overcoming chemoresistance to heighten the therapeutic effect. This work proposes a conceptual framework of antibacterial-augmented antitumor nanomedicine for refined cancer-therapeutic efficacy by modulating intratumoral bacteria to enhance therapeutic responses of chemotherapy, opening new horizons on nanomedicine design for more effective tumor therapy.

Electrical Resistance in a Composite of Ultra-Small Silver Nanoparticles Embedded in Gold Nanostructures: Implications for Interface-Enabled Functionality

Ultrasmall nanoparticles of noble metals, in particular silver (Ag) or gold (Au), have been extensively investigated for their optical, magnetic, chemical, and physical properties, but assembling such structures in an electrically conducting metallic matrix, where the physical dimension of individual nanoparticles plays a decisive role, has remained elusive. This is because true metallic conduction through individual or clusters of metallic nanoparticles is often prevented by tunnel barriers due to surface-protecting ligands, oxidation, etc. By removing the chemical remnants, these challenges have been overcome in a cross-linked nanohybrid assembly made of ultrasmall silver nanoparticles (AgNPs) in an all-metallic matrix of Au. The resulting Ag–Au nanohybrid exhibits metallic behavior where the resistance decreases with decreasing temperature, for all radii (rAg ≫ 1–3 nm) and concentrations of AgNPs (average center-to-center distance between two AgNPs d ≈ 4–6 nm) from room to cryogenic temperatures (≈ 6 K). Strikingly, we observe the electrical resistivity of the hybrid to scale directly with the net surface area of the embedded AgNPs, thereby achieving residual resistivity as high as 40 μΩ.m, which is more than 2 orders of magnitude larger than that of crystalline Au. Our experiment outlines a novel method of designing metals with nanostructured interfaces that can lead to new phenomena and functionality.

Ultra-Small Silver Nanoparticles: A Sustainable Green Synthesis Approach for Antibacterial Activity

The present study centers on the synthesis of ultra-small silver nanoparticles (AgNPs) with antibacterial properties using citrus peel residues (orange, lemon, and grapefruit) as reducing and stabilizing agents, and on assessing their antibacterial activity against multidrug-resistant clinical Staphylococcus aureus. The synthesized AgNPs were analyzed by various techniques, including UV-Vis spectroscopy, SAED, TEM, XRD, FTIR, and Raman. The results demonstrate the formation of ultra-small, monodisperse, quasi-spherical AgNPs with an average particle size of 2.42 nm for AgNPs produced with mixed extracts. XRD analysis indicated that the AgNPs have a crystal size of 9.71 to 16.23 nm. The AgNPs exhibited potent inhibitory activity against resistant S. aureus, with a minimum inhibitory concentration (MIC) of 15.625 to 62.50 ppm. The findings suggest that the ultra-small nanometer size of the AgNPs could be attributed to the synthesis method that employs ambient conditions and the presence of polyphenolic compounds from citrus peel. Consequently, AgNPs obtained through sustainable green synthesis hold significant potential in combating clinical multi-resistant bacterial strains that are challenging to treat and eradicate. This approach also contributes to the revaluation of citrus residues in the region, which is an ongoing environmental issue today.

Enzyme-responsive polycationic silver nanocluster-loaded PCL nanocomposites for antibacterial applications

Infections caused by pathogenic bacteria such as Gram-positive Staphylococcus aureus and Gram-negative Pseudomonas aeruginosa remain a significant healthcare challenge. In this study, we developed an enzyme-responsive antibacterial nanomaterial that delivers antibacterial agents only in the presence of bacterial lipase. This was achieved by first synthesizing highly potent ultra-small silver nanoparticles with an average core size of 1.6 ± 0.2 nm and then embedding them into polycaprolactone nanoparticles (pAgNCs@PCL) via the water in oil in water approach. The pAgNCs@PCL nanoparticles had an average diameter of 274.1 ± 60.1 nm and a silver nanoparticle encapsulation efficiency of 15.7 ± 1.3%. We demonstrated that silver released from the pAgNCs@PCL was selectively triggered by lipase-expressing strains of P. aeruginosa and S. aureus. As expected, there was no antibacterial action observed against E. coli DH5α, which does not express lipase. The pAgNCs@PCL nanoparticles exhibited minimal cytotoxicity against human fibroblast cells suggesting good biocompatibility. This study resulted in a highly potent on-demand delivery system that can be potentially incorporated into healthcare products and devices to prevent and/or treat infections.

Green tubular micro/nano architecture constructed by in-situ planting of small AgNPs on Kapok fiber for oil spill recovery, smart oil–water separation and multifunctional applications

The ubiquitous existence of harmful contaminants in water is recognized as a major threat to aquatic ecosystems and human health, and renewable, economical, and superefficient new materials are needed to eliminate these dangers. Here, the ultrasmall silver nanoparticles (AgNPs) anchored Kapok fiber (KF) (KF/AgNPs) composite capable of efficiently separating various oil–water systems and eliminating other pollutants or bacteria was prepared by a green self-reducing reaction process using natural KF as the “microreactor” and water as the only solvent. The introduction of AgNPs endows KF/AgNPs with significantly improved liquid storage capacity, underwater superoleophobicity and underoil superhydrophobicity, so it shows excellent switchable oil–water separation capability. The oil–water separation efficiencies under gravity reached 99.90 % for the oil-in-water (O/W) emulsion (water flux: 1300 L·m−2·h−1), 99.91 % for the water-in-oil (W/O) emulsion (oil flux: 1500 L·m−2·h−1), and 99.80 % for the immiscible oil–water mixture (flux: 1900 L·m−2·h−1). In addition, KF/AgNPs composite can serve as absorbents to remove oil slicks from sewage (removal efficiency: 99.95 %; absorption capacity: 42.3 g/g) and adsorbents to rapidly remove microplastics in actual natural waters (concentration: 10 mg/L and can inhibit the growth of E. coli bacteria. After use, approximately 96.4 % of Ag was recovered from spent composite, and an excellent biochar adsorbent for the dye was obtained simultaneously.

Photocatalytic degradation of azo dyes by ultra-small green synthesized silver nanoparticles

BackgroundThe presence of toxic dyes in wastewater is a serious problem for human health. In this work, the degradation of commercial azo dyes sold over-the counter in Mexico was studied, using as a photocatalyst ultra-small silver nanoparticles (AgNPs) green synthesized. MethodsFor the first time, the successful green synthesis of ultra-small AgNPs using, as both reducing-stabilizing agents (RSa), the aqueous extract of Pelargonium hortorum (Phf) flower or Allium fistulosum (Afs) stem, is reported. AgNPs were characterized by ultraviolet-visible (UV–Vis) and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopies, field emission scanning electron microscopy-energy dispersive spectroscopy (FE-SEM-EDS), and field emission transmission electron microscopy (FE-TEM). Significant findingsThe morphology of the AgNPs, in both cases, are spherical. AgNPs synthesized with Phf (AgNPs/Phf), which have a mode size of 2 nm (41.9%) and a bandgap of 2.38 eV, resulted in a photocatalytic degradation efficiency of 95%. On the other hand, AgNPs synthesized with Afs (AgNPs/Afs), which have a mode size of 0.6 nm (37.8%) and a bandgap of 2.43 eV, presented a photocatalytic efficiency of 100%. The photocatalytic efficiency and bandgap of the synthesized AgNPs were found to be inversely proportional to the AgNPs size; i.e. the smaller the AgNPs, the higher photocatalytic degradation, and bandgap exhibited.

Bacteria-Activated Dual pH- and Temperature-Responsive Hydrogel for Targeted Elimination of Infection and Improved Wound Healing.

Antibacterial treatment that provides on-demand release of therapeutics that can kill a broad spectrum of pathogens while maintaining long-term efficacy and without developing resistance or causing side effects is urgently required in clinical practice. Here, we demonstrate the development of a multistimuli-responsive hydrogel, prepared by cross-linking N-isopropylacrylamide with acrylic acid and loaded with ultrasmall silver nanoparticles (AgNPs), offering the on-demand release of Ag+ ions triggered by changes in the wound microenvironment. We demonstrate that this dual-responsive hydrogel is highly sensitive to a typical wound pH and temperature change, evidenced by the restricted release of Ag+ ions at acidic pH (<5.5) while significantly promoting the release in alkaline pH (>7.4) (>90% release). The pH-dependent release and antibacterial effect show minimal killing at pH 4 or 5.5 but dramatically activated at pH 7.4 and 10, eliminating >95% of the pathogens. The in vivo antibacterial efficacy and safety showed a high potency to clear Staphylococcus aureus wound infection while significantly accelerating the wound healing rate. This multifunctional hydrogel presents a promising bacteria-responsive delivery platform that serves as an on-demand carrier to not only reduce side effects but also significantly boost the antibacterial efficiency based on physiological needs. It offers great potential to improve the way wound infections are treated with direct clinical implications, providing a single platform for long-lasting application in wound management.

UV-irradiating synthesis of cyclodextrin-silver nanocluster decorated TiO2 nanoparticles for photocatalytic enhanced anticancer effect on HeLa cancer cells.

Titanium dioxide (TiO2) has emerged as a viable choice for several biological and environmental applications because of its high efficiency, cheap cost, and high photostability. In pursuit of this purpose, the research of its many forms has been influenced by these unique aspects. The development of novel TiO2-based hybrid materials with enhanced photocatalytically induced anticancer activity has gained tremendous attention. Here, we have developed a novel photocatalytic material (TiO2–Ag NPs@-CD) by decorating ultrasmall silver nanoparticles (Ag NPs) with per-6-thio-β-cyclodextrin (SH-β-CD) on TiO2 NPs. TiO2–Ag NPs@-CD were characterized by employing various characterization techniques and evaluated for their anticancer activity against HeLa cancer cells using an MTT assay. The biocompatibility of the designed nanoparticles was determined on two normal cell lines, namely, 3T3 and human mesenchymal stem cells (hMSCs). The results show that the TiO2–Ag NPs@-CD induced superior cytotoxic effects on HeLa cancer cells at a concentration of 64 μg/ml. Live-dead staining and oxidative stress investigations demonstrated that cell membrane disintegration and ROS-induced oxidative stress generated by TiO2-Ag NPs@-CD inside HeLa cancer cells are the contributing factors to their exceptional anti-cancer performance. Moreover, TiO2-Ag NPs@-CD exhibited good biocompatibility with 3T3 and hMSCs. These results indicated that the combination of all three components—a silver core, SH-β-CD ligands, and TiO2 nanoparticles—produced a synergistic anticancer effect. Hence, the TiO2-Ag NPs@-CD is a promising material that can be employed for different biological applications.

Impact of ultra-small silver nanoparticles of 2 nm (AgNP2) on neutrophil biology: AgNP2 alter the actin cytoskeleton and induce karyorrhexis by a mitogen-activated protein kinase-dependent mechanism in vitro and transitorily attract neutrophils in vivo

Silver (Ag) is known as an antibacterial agent and there is a growing interest to use silver nanoparticles (AgNPs) in a variety of medical applications and other sectors. Some studies reported that one of the undesired effects of AgNPs is inflammation and that these NPs can alter the biology of neutrophils. Since it is commonly accepted that the more NPs are small, the more toxic they are the aim of this study was to determine the impact of ultra-small silver nanoparticles of 2 nm (AgNP2) on the biology of neutrophils, key player cells in inflammation. We report that AgNP2 are potent neutrophil activators as they rapidly induce actin polymerization and dismantling the actin network. Although AgNP2 are not necrotic for neutrophils and do not induce ROS production, kinetic studies reveal that AgNP2 are rapid inducer of apoptosis. Pyknosis (mainly 1–2 large nuclear dots) was observed after only 1h of treatment followed by karyorrhexis (several small dots) and by a complete nuclear dissolution leading to anuclear neutrophils after 6h. These observations are not associated with the release of silver ions since treatment of neutrophils with 1–50 μg/ml AgNO3 (as a source of Ag+) did not induce any apparent changes. AgNP2 induce p38 and Erk-1/2 mitogen-activated protein kinase (MAPK) and although karyorrhexis was markedly reversed by MAPK inhibitors, the cell nuclei remain with a pyknotic-like phenotype but do not return to the characteristic polylobed nucleus. Using the murine air pouch model of inflammation AgNP2 were found to induce a neutrophil influx. Our data indicate that AgNP2 are potent neutrophil activators targeting the actin cytoskeleton and the mechanism involved for inducing apoptosis is rapid, complex, and partially includes MAPK pathways. Therefore, the ultra-small AgNP2 are more potent than larger ones for inducing apoptosis and they can transitorily attract neutrophils in vivo.

One-step synthesis of ultra-small silver nanoparticles-loaded triple-helix β-glucan nanocomposite for highly catalytic hydrogenation of 4-nitrophenol and dyes

Finding an eco-friendly homogeneous catalyst with high efficiency to rapidly clean up dyes and 4-nitrophenol in wastewater is urgently to be solved. Herein, we ingeniously designed a stable and reusable homogeneous catalyst of ultra-small silver nanoparticles (AgNPs)-loaded triple-helix β-glucan (BFP) nanomaterial (BFP-Ag) via one-step reduction in dimethyl sulfoxide with BFP as the reductant. Moreover, BFP triplex formed nanotubes, acting as a matrix to disperse and stabilize AgNPs through Ag-O bonds in water. The ultra-small AgNPs (2.8–10 nm) were embedded into the hollow cavity of BFP nanotubes indicated by the aqueous solution color. BFP-Ag effectively catalyzed reduction of 4-nitrophenol with the higher catalytic efficiency for smaller size of AgNPs. The catalytic turnover frequencies of BFP-Ag nanocomposite for reduction of Congo Red, Methyl Orange, Rhodamine B and 4-nitrophenol were determined to be 1423.02 h−1, 349.52 h−1, 452.78 h−1 and 1335.89 h−1, respectively, which were far higher than those of the most reported catalysts. BFP-Ag maintained over 95% conversion after eight continuous cycles and the entire catalytic and recovery process could be achieved by a simple filter device for the practice applications. The hot filtration and recovery test verified the homogeneity and stability of BFP-Ag. This work provides a novel strategy for designing eco-friendly homogeneous catalysts in wastewater treatment and expands the application of natural polysaccharides in the synthetic catalysis.

New types of hyperbranched 1,2,3-triazole-alkoxysiloxane functional polymers for metal embedded nanocomposite surface coatings.

In this study, using the "click-chemistry" azide-alkyne cycloaddition reaction, two new types of polymers, namely, water-soluble amine-functional and water-insoluble pyridine-functional hyperbranched 1,2,3-triazoleorganoethoxysiloxane polymers, capable of stabilizing ultra-small silver nanoparticles and efficient for chemical surface modification were synthesized and characterized by 1H-NMR, 13C-NMR, 29Si-NMR and FT-IR spectroscopy, MALDI and GPC. Coordinatively active hetero-organic polymers with a flexible branched polyethoxysiloxane backbone bearing chelating 1,2,3-triazolyl-dimethylamine and -pyridine conjugated functional groups were exploited towards coordination with Ag+ metal ions, and formation and stabilization of narrowly dispersed silver nanoparticles (Ag-NPs) obtained in the process of radiation induced metal ion reduction. The influence of the chemically assisted radiation process on the Ag-NP size and size distribution was investigated. Hyperbranched polyorganoethoxysiloxanes loaded with Ag-NPs were covalently cross-linked on a Stöber silica surface, demonstrating the efficiency of the developed hetero-organic functional polymers in the preparation of functional nanocomposite coatings for various applications (heterogeneous catalytic systems, antibacterial materials, nanoparticle-based optical sensing devices, etc.). The nanocomposites were investigated and characterized by TEM-EDS, DLS, UV-Vis spectroscopy and 29Si MAS NMR spectroscopy.

Development of pH-responsive nanocomposites with remarkably synergistic antibiofilm activities based on ultrasmall silver nanoparticles in combination with aminoglycoside antibiotics

Bacterial biofilms are responsible for many chronic infections because antibacterial agents exhibit poor penetration into the dense matrix barrier and cannot easily reach the internal bacteria. Herein, we reported pH-responsive nanocomposites (PDA@Kana-AgNPs) that could penetrate and disperse biofilms, which were synthesized by the combination of ultrasmall silver nanoparticles (AgNPs) and kanamycin, and then coating with polydopamine. Confocal fluorescence imaging indicated that PDA@Kana-AgNPs could respond to the acidic microenvironment of biofilms, leading to biofilm-triggered on- demand drug release in situ. The zone of inhibition test and Resazurin assay showed that the combination of kanamycin and AgNPs had greater antimicrobial activity against test strains (Staphylococcus aureus, Streptococcus pneumoniae, Pseudomonas aeruginosa, and Escherichia coli BL21) than when applied separately. The crystal violet staining test demonstrated that biofilms were effectively dispersed by the proposed nanocomposites. Biocompatibility was also evaluated, which showed that PDA@Kana-AgNPs were non-toxic to mammalian cells. Therefore, the proposed pH-responsive nanocomposites held great potential for efficient antibiotics delivery and showed synergistic antibacterial and antibiofilm activities. This strategy could also be used to encapsulate a variety of antibiotics in combination with other drugs or materials, thereby showing therapeutic potential in preventing biofilm-related infections and realizing fluorescence imaging in situ.

Metal-Ligand Interface and Internal Structure of Ultrasmall Silver Nanoparticles (2 nm).

Ultrasmall silver nanoparticles were prepared by reduction with NaBH4 and surface-terminated with glutathione (GSH). The particles had a solid core diameter of 2 nm as shown by transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). NMR-DOSY gave a hydrodynamic diameter of 2 to 2.8 nm. X-ray photoelectron spectroscopy (XPS) showed that silver is bound to the thiol group of the central cysteine in glutathione under partial oxidation to silver(+I). In turn, the thiol group is deprotonated to thiolate. X-ray powder diffraction (XRD) together with Rietveld refinement confirmed a twinned (polycrystalline) fcc structure of ultrasmall silver nanoparticles with a lattice compression of about 0.9% compared to bulk silver metal. By NMR spectroscopy, the interaction between the glutathione ligand and the silver surface was analyzed, also with 13C-labeled glutathione. The adsorbed glutathione is fully intact and binds to the silver surface via cysteine. In situ 1H NMR spectroscopy up to 85 °C in dispersion showed that the glutathione ligand did not detach from the surface of the silver nanoparticle, i.e. the silver-sulfur bond is remarkably strong. The ultrasmall nanoparticles had a higher cytotoxicity than bigger particles in in vitro cell culture with HeLa cells with a cytotoxic concentration of about 1 μg mL-1 after 24 h incubation. The overall stoichiometry of the nanoparticles was about Ag∼250GSH∼155.

Multifunctional ultrasmall AgNP hydrogel accelerates healing of S. aureus infected wounds

The increasing emergence of antibiotic resistance coupled with the limited effectiveness of current treatments highlights the need for the development of new treatment modalities. Silver nanoparticles (AgNPs) are a promising alternative with broad-spectrum antibacterial activity. However, the clinical translation of AgNPs have been hampered primarily due to the delivery of unsafe levels of silver ions (Ag+) resulting in cellular toxicity and their susceptibility to aggregation resulting in loss of efficacy. Here, we describe a safe and effective, thermo-responsive AgNP hydrogel that provides antibacterial effects in conjunction with wound promoting properties. Using a murine model of wound infection, we demonstrate that the applied AgNP hydrogel to the wound (12 µg silver) not only provides superior bactericidal activity but also reduces inflammation leading to accelerated wound closure when compared to industry-standard silver sulfadiazine (302 µg silver). The AgNP hydrogel-treatment significantly accelerated wound closure at day 4 post-infection (56 closure) compared to both blank hydrogel or Ag SD (74% and 91% closure respectively) with a concurrent increase in PCNA-positive proliferating cells corresponding with a significant 32% improvement in wound re-epithelization compared to the blank hydrogel. Treatment of infected wounds with AgNP hydrogel also decreased neutrophil infiltration, increased anti-inflammatory Ym-1 positive M2 macrophages, and reduced the number of caspase-1 positive apoptotic cells. Therefore, this novel multifunctional AgNP thermo-responsive hydrogel is potentially a safe and effective treatment at much lower concentration for the treatment of wound infections. Statement of significanceIn this study, we describe the development of a multifunctional thermo-responsive hydrogel of ultrasmall silver nanoparticles (AgNPs) for controlled and optimized delivery of silver to infected wounds. The in vivo biological effects of the developed hydrogel showed significant S. aureus elimination from infected mouse wounds compared to a commercial antibacterial formulation. The developed AgNP hydrogel optimally regulates inflammatory responses to promote wound healing as indicated by increased cell proliferation and wound re-epithelization. Additionally, AgNP hydrogel shows significant potential in regulating neutrophil infiltration while increasing levels of anti-inflammatory M2 macrophages and reduces the number of apoptotic cells. Therefore, the multifunctional properties of the developed AgNP thermo-responsive hydrogel offers great clinical potential to control bacterial infections and promote wound healing.

Non-local Quantum Plasmon Resonance in Ultra-small Silver Nanoparticles

Understanding the mechanisms of light–matter interactions in ultra-small plasmonic nanoparticles (USNP) represents a major challenge because of the importance of size dependence and quantum effects. The plasmon resonance in such small metallic nanoparticles (< 5 nm) exhibits substantial deviation from classical theory predictions, with evident frequency shifts to a higher energy. This is due to the quantum nature of the free charge carriers and the dynamic response of metallic nanoparticle to the self-consistent electromagnetic fields. Such phenomena have so far been poorly understood in experiments while classical theory has mostly focused on nanostructures and sidestepped the size dependence. Here we report a quantum mechanical model of the metal permittivity to describe the USNP behaviour and experimental evidence. The proposed non-local quantum model of the permittivity for the propagation of plasmon waves in quantum-confined silver nanoparticles has no size limitations in the UNSP range.