Role of base in the formation of silver nanoparticles synthesized using sodium acrylate as a dual reducing and encapsulating agent

Synthesis and Characterization of Lignin-Silver Nanoparticles

Metal nanoparticle synthesis via environmentally friendly methods is gaining interest for their potential advantages over conventional physico-chemical approaches. Herein, we propose a robust green synthesis route for lignin-modified silver nanoparticles, utilizing the recovery of lignin as a renewable raw material and exploring its application in valuable areas. Through a systematic approach combining UV-Vis spectroscopy with AAS and DLS, we identified repeatable and scalable reaction conditions in an aqueous solution at pH 11 for homogeneous silver nanoparticles with high uniformity. The TEM median sizes ranged from 12 to 15 nm with circularity between 0.985 and 0.993. The silver nanoparticles yield exceeded 0.010 mol L-1, comparable with traditional physico-chemical methods, with a minimal loss of silver precursor ranging between 0.5 and 3.9%. Characterization by XRD and XPS revealed the presence of Ag-O bonding involving lignin functional groups on the pure face-centered cubic structure of metallic silver. Moreover, the lignin-modified silver nanoparticles generated a localized thermal effect upon near-infrared laser irradiation (808 nm), potentially allowing for targeted applications in the biomedical field. Our study showcases the potential of lignin as a renewable reducing and capping agent for silver nanoparticle synthesis, addressing some shortcomings of green synthesis approaches and contributing to the development of suitable nanomaterials.

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.

Targeted color design of silver-gold alloy nanoparticles

This research article focuses on the targeted color design of silver-gold alloy nanoparticles (NPs), employing a multivariate optimization approach. NP synthesis involves interconnected process parameters, making independent variation challenging. Data-based property-process relationships are established to optimize optical properties effectively. We define a color target, employ a green chemical co-reduction method at room temperature and optimize process parameters accordingly. The CIEL*a*b* color space (Commission Internationale de l'Éclairage - International Commission on Illumination) and Euclidean distances facilitate accurate color matching to establish the property-process relationship. Concurrently, theoretical Mie calculations explore the structure-property relationship across particle sizes, concentrations, and molar gold contents. The theoretically optimal structure agrees very well with experimental particle structures at the property-process relationship's optimum. The data-driven property-process relationship provides valuable insights into the formation mechanism of a complex particle system, sheds light on the role of relevant process parameters and allows to evaluate the practically available property space. Model validation beyond the original grid demonstrates its robustness, yielding colors close to the target. Additionally, Design of Experiments (DoE) methods reduce experimental work by threefold with slight accuracy trade-offs. Our novel methodology for targeted color design demonstrates how data-based methods can be utilized alongside structure-property relationships to unravel property-process relationships in the design of complex nanoparticle systems and paves the way for future developments in targeted property design.

Polymeric coating doped with nanomaterials for functional impact on different substrates

Microorganism contamination on substrate surfaces is arousing increasingly concern as a serious health issue. In this research work, antimicrobial water-based acrylic paint containing silver nanoparticles (Ag NPs) was prepared using the facile Ag+ in situ reduction process, in which AgNO3 and reducing agent sodium acrylate were refluxed with acrylic polymeric solution to obtain an antimicrobial and antifungal polymeric material for substrate coating. The Synthesized antimicrobial and antifungal water-based acrylic paint were characterized by different spectroscopic techniques. The FTIR and UV-Visible spectroscopic analyses were investigated to study the water-based acrylic paint structure as well as the significant impact of Ag NPs on the paint matrix. The UV-Visible and FTIR Spectra peak shows successful integration of Ag NPs within the polymer matrix without altering the core functional groups of the paint. The water based acrylic paint exhibited a strong antimicrobial activity, revealed substantial inhibition zones against all four strains of Gram negative represented by Escherichia coli, Acinetobacter baumannii, Klebsiella pneumoniae and Gram-positive represented by Bacillus cereus. The coated film on substrate also shows great inhibition zone which exhibit a strong antimicrobial activity. Moreover, water based acrylic paint also exhibited a great antifungal activity, revealed substantial zone of inhibition against the Aspergillus niger, Aspergillus terreus and Rhizopus arrhizus fungal strains. Also, the coated film showed the best adhesion at 50% and 80% solution of polymeric coating sample as compared to pure or very dilute sample coating. This innovative approach has the potential to revolutionize varies industries from healthcare to construction.

Evaluation of Antibacterial, Antioxidant, Anti-inflammatory and Anticancer Efficacy of Titanium-Doped Graphene Oxide Nanoparticles

INTRODUCTION

The current development of nanoparticles (NPs) with significant antibacterial properties, low cost and low toxicity has made it possible to develop novel techniques for treatments in the medical field. The titanium metal oxide, when combined with a carbonaceous material like graphene, which has excellent absorbing capacity, is efficient in loading drugs and thus helps in drug delivery and also in biomedical applications like anticancer, anti-inflammatory, antioxidant, and antibacterial activities.

MATERIALS AND METHODS

Titanium-doped graphene oxide nanoparticles (Ti/GO-NPs) were processed by the one-pot synthesis method; further characterization was performed by using UV-visible spectroscopy, Fourier transform-infrared spectroscopy (FT-IR), field emission electron microscopy (FE-SEM), and energy-dispersive X-ray spectroscopy (EDX) analysis and biomedical applications like anticancer, anti-inflammatory, antioxidant and antibacterial activities.

RESULTS

The synthesized end product of Ti/GO-NPs showed a creamy white appearance. Subsequent characterization studies of UV-Vis spectroscopy revealed a peak level of 373 nm at 24 hours and 404 nm after 48 hours. FT-IR analysis exhibited a broad absorption band within the range of 1000-3500 cm-1, which was attributed to various chemical compounds of C-Br, C-I stretching, C=C bending, S=O stretching, O=H stretching, C=C stretching, H bonded and OH stretching to different absorbance wavelength ranges. SEM analysis exhibited quasi-spherical-shaped Ti/GO-NPs with an average particle size of 50- 100 nm and EDX analysis showed the elemental composition of 32.3% titanium 43.9% oxygen and 2.5% carbon. The antibacterial activity showed moderate activity against Staphylococcus aureus and no activity against Pseudomonas aeruginosa, Enterococcus faecalis and E. coli. The antioxidant activity exhibited 88% at 50 µg/mL concentration, the anti-inflammatory activity revealed 80% at 80 µg/mL concentration and the anticancer activity showed 21% at 150 µg/mL concentration.

CONCLUSION

The characterization and biomedical application conclude that a combination of Ti/GO-NPs will be efficient in drug delivery. The study showed moderate antibacterial activity and significant antioxidant, anti-inflammatory and anticancer activities. Considering their physiochemical properties, absorption capacity and mechanism of drug delivery, Ti/GO-NPs can be incorporated into various applications in the medical field.

Eco-friendly Synthesis of Silver Nanoparticles and its Application in Hydrogen Photogeneration and Nanoplasmonic Biosensing

Environmentally friendly methods for silver nanoparticles (AgNPs) synthesis without the use of hazardous chemicals have recently drawn attention. In this work, AgNPs have been synthesized by microwave irradiation using only honey solutions or aqueous fresh pink radish extracts. The concentrations of honey, radish extract, AgNO3 and pH were varied. AgNPs presented mean sizes between 7.0 and 12.8 nm and were stable up to 120 days. The AgNPs were employed as co-catalyst (TiO2 @AgNPs) to increase the hydrogen photogeneration under UV-vis and only visible light irradiation, when compared to pristine TiO2 NPs. The prepared photocatalyst also showed hydrogen generation under visible light. Additionally, AgNPs were used to assemble a nanoplasmonic biosensor for the biodetection of extremely low concentrations of streptavidin, owing to its specific binding to biotin. It is shown here that green AgNPs are versatile nanomaterials, thus being potential candidates for hydrogen photogeneration and biosensing applications.

Green room temperature synthesis of silver-gold alloy nanoparticles

Metallic alloy nanoparticles (NPs) exhibit interesting optical, electrical and catalytic properties, dependent on their size, shape and composition. In particular, silver-gold alloy NPs are widely applied as model systems to better understand the syntheses and formation (kinetics) of alloy NPs, as the two elements are fully miscible. Our study targets product design via environmentally friendly synthesis conditions. We use dextran as the reducing and stabilizing agent for the synthesis of homogeneous silver-gold alloy NPs at room temperature. Our approach is a one-pot, low temperature, reaction-controlled, green and scalable synthesis route of well-controlled composition and narrow particle size distribution. The composition over a broad range of molar gold contents is confirmed by scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy (STEM-EDX) measurements and auxiliary inductively coupled plasma-optical emission spectroscopy measurements (ICP-OES). The distributions of the resulting particles in size and composition are obtained from multi-wavelength analytical ultracentrifugation using the optical back coupling method and further confirmed by high-pressure liquid chromatography. Finally, we provide insight into the reaction kinetics during the synthesis, discuss the reaction mechanism and demonstrate possibilities for scale-up by a factor of more than 250 by increasing the reactor volume and NP concentration.

Application of silver nanoparticles synthesized through varying biogenic and chemical methods for wastewater treatment and health aspects

Nanotechnology uses biological and non-biological materials to create new systems at the nanoscale level. In recent years, the use of silver nanomaterials has attracted worldwide attention thanks to their wide range of applications as catalysts in several environmental processes including the degradation of organic pollutants and medicinal biotechnology. This study reports the synthesis of silver nanoparticles (AgNPs) through different methods including the biogenic methods based on leaf extract of Conocarpus erectus and a bacterial strain Pseudomonas sp. as well as chemically based abiotic method and comparison of their dye degradation potential. The synthesis of AgNPs in all samples was confirmed by UV-visible spectroscopy peaks at 418-420 nm. Using scanning electrom microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), X-ray differaction (XRD), and X-ray photoelectron spectroscopy (XPS), the biologically synthesized AgNPs were characterized as spherical shape of material with capping proteins that were involved in the stabilization of nanoparticles (NPs). The biologically synthesized AgNPs showed higher degradation (< 90%) of dyes as compared to chemically synthesized NPs. A prominent reduction of total dissolved solids (TDS), electrical conductivity (EC), pH, and chemical oxygen demand (COD) in textile wastewater spiked with reactive black 5 and reactive red 120 was observed by biologically synthesized AgNPs. AgNPs synthesized by Conocarpus erectus and Pseudomonas sp. also showed better characteristic anticancer and antidiabetic activities as compared to chemically synthesized ones. The results of this study suggested that C. erectus and Pseudomonas sp. based AgNPs can be exploited as an eco-friendly and cost-efficient materials to treat the wastewater and potential other polluted environments as well as to serve the medicinal field.

Gold and silver nanoparticles functionalized with 4',7-dihydroxyflavone exhibit activity against Leishmania donovani

Leishmaniasis is a neglected tropical disease that has been burdening the world for over a century. Though there are drugs to treat leishmaniasis, the repertoire suffers several drawbacks like toxicity and low therapeutic value. Therefore, there is a rising concern to develop new anti-leishmanial strategies. In this study, we report, for the first time, the one-pot synthesis method and functionalization of gold and silver nanoparticles with 4',7-dihydroxyflavone (Au-47DHF and Ag-47DHF)) and their anti-leishmanial activity. Oval and spherical-shaped Au-47DHF nanoparticles were obtained with an average size of 5.8 ± 0.1 nm and while synthesized dodecahedron-shaped Ag-47DHF had an average size of 25.1 ± 1 nm. The zeta potential of Au-47DHF and Ag-47DHF were measured to be stable with values of 40 mV and 60 mV, respectively. The functionalization of nanoparticles with 4',7-dihydroxyflavone was confirmed by FTIR spectra. Both Au-47DHF and Ag-47DHF exhibited promising anti-leishmanial activity against the promastigote forms with IC₅₀ values of 0.1226 ± 0.02 µg/ml and 0.8483 ± 0.14 µg/ml, respectively. The nanoparticles were also capable of anti-intracellular amastigote activity with 0.121 ± 0.36 µg/ml and 0.215 ± 0.85 µg/ml for Au-47DHF and Ag-47DHF, respectively. Interestingly, the treatment with Au-47DHF and Ag-47DHF nanoparticles generated high ROS concentrations in the parasites suggesting a ROS-mediated anti-leishmanial activity of Au-47DHF and Ag-47DHF. Concluding from the results, we present here a novel synthesis method of Au-47DHF and Ag-47DHF nanoparticles that have immense potential to be anti-leishmanial agents.

A highly sensitive colorimetric sensing platform based on silver nanocomposites for alkaline phosphatase

Alkaline phosphatase (ALP) plays significant roles in regulating intracellular processes and is an important biomarker connected to several diseases. In this work, one facile and sensitive sensing platform based on CQD-silver nanocomposites (CQD-silver NPs) for colorimetric detection of alkaline phosphatase (ALP) was introduced. ALP triggers the removal of the phosphate group of ascorbic acid 2-phosphate (AA2P), which is then transformed into ascorbic acid (AA). The as-obtained AA can easily cause significant aggregation of monodispersed NPs and cause the system color to turn from bright yellow to gray. Based on the color change of the ratio of 490 nm/630 nm, ALP was sensitively and selectively detected. Under the optimum, the established method showed linearity for ALP in the range of 0.1-50 U L^-1 and the detection limit was low at 0.035 U L^-1, and it was subjected to ALP inhibitor screening from goji berry extract. These results indicated that the colorimetric system can be used as a simple tool for visual and fast evaluation of ALP activity as well as providing an alternative to screen ALP inhibitors.

Detailed Kinetic and Mechanistic Study for the Preparation of Silver Nanoparticles by a Chemical Reduction Method in the Presence of a Neuroleptic Agent (Gabapentin) at an Alkaline pH and its Characterization

For the very first time, a detailed kinetic study for the preparation of silver nanoparticles (silver NPs) by neuroleptic agent gabapentin (GBP) in the absence of a stabilizer has been reported in this investigation. This paper is devoted to the preparation of silver nanoparticles by a chemical reduction method in which gabapentin acts as both a reductant and a stabilizer, and AgNO₃ is used as a source of Ag⁺ ions and NaOH for maintaining the alkaline medium. A UV-visible spectrophotometer is used to monitor the progress of the reaction kinetics in an aqueous medium by changing the concentration of different variables such as AgNO₃, NaOH, and gabapentin at 40 °C. It is found that the reaction rate follows a pseudo-first-order reaction. The thermodynamic activation parameters were also studied at five different temperatures (303, 308, 313, 318, and 323 K) and used in the support of the proposed mechanistic scheme for the formation of silver nanoparticles. The prepared silver nanoparticles were characterized using different techniques: UV-visible spectrophotometry, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and powder X-ray diffraction. The average particle size was observed in the range of 5-45 nm.

Ag/LDH-itaconic acid-gellan gam nanocomposites: Facile and green synthesis, characterization, and excellent catalytic reduction of 4-nitrophenol

The catalytic reduction reaction is one of the most commonly used solutions to convert high-risk contaminants into safe or low-risk materials. Today, with the increasing water pollution, the urgent need for efficient and effective catalysts is felt more than ever. For this purpose, for the first time, a green catalyst composed of silver nanoparticles anchored on itaconic acid-modified Ca-Al layered double hydroxide/gellan gum nanocomposite (Ag/LDH-ITA-GG NC) was prepared from a green approach without the use of any toxic organic solvents. To gain an in-depth insight into the physicochemical properties of the catalyst, different techniques including nitrogen adsorption-desorption isotherms, FESEM/mapping, FTIR, TGA, and XRD were used. The catalytic performance of the Ag/LDH-ITA-GG NC toward 4-nitrophenol reduction by NaBH₄ was investigated. The calculated values of the apparent rate constant for this reaction are 0.2142 min^-1 (for 1.0 mg of the catalyst), 0.2375 min^-1 (for 3.0 mg of the catalyst), and 0.2550 min^-1 (for 5.0 mg of the catalyst), indicating that the catalytic conversion of 4-nitrophenol to 4-aminophenol on the Ag/LDH-ITA-GG NC catalyst follows the pseudo-first-order kinetics and is comparable to the previous findings in the literature. The results of this study indicated that Ag/LDH-ITA-GG NC can potentially be utilized as an auspicious high efficient green catalyst for the reduction of pollutants like 4-nitrophenol.

Effective Intratumoral Retention of [103 Pd]AuPd Alloy Nanoparticles Embedded in Gel-Forming Liquids Paves the Way for New Nanobrachytherapy

Local application of radioactive sources as brachytherapy is well established in oncology. This treatment is highly invasive however, due to the insertion of millimeter sized metal seeds. The authors report the development of a new concept for brachytherapy, based on gold-palladium (AuPd) alloy nanoparticles, intrinsically radiolabeled with ¹⁰³ Pd. These are formulated in a carbohydrate-ester based liquid, capable of forming biodegradable gel-like implants upon injection. This allows for less invasive administration through small-gauge needles. [¹⁰³ Pd]AuPd nanoparticles with sizes around 20 nm are prepared with radiolabeling efficiencies ranging from 79% to >99%. Coating with the hydrophobic polymer poly(N-isopropylacrylamide) leads to nanoparticle diameters below 40 nm. Dispersing the nanoparticles in ethanol with water insoluble carbohydrate esters gives "nanogels", a low viscosity liquid capable of solidifying upon injection into aqueous environments. Both nanoparticles and radioactivity are stably retained in the nanogel over 25 days (>99%) after formation in aqueous buffers. Animals bearing CT26 murine tumors are injected intratumorally with 25 MBq of the ¹⁰³ Pd-nanogel, and display tumor growth delay and significantly increase median survival times compared with control groups. Excellent retention in the tumor of both the ¹⁰³ Pd and the nanoparticle matrix itself is observed, demonstrating a potential for replacing currently used brachytherapy seeds.

Substrate-Independent, Regenerable Anti-Biofouling Coating for Polymeric Membranes

Biofouling is a common but significant issue in the membrane process as it reduces permeate flux, increases energy costs, and shortens the life span of membranes. As an effective antibacterial agent, a small amount of silver nanoparticles (AgNPs) immobilized on membrane surfaces will alleviate the membrane from biofouling. However, loading AgNPs on the membrane surface remains a challenge due to the low loading efficiency or the lack of bonding stability between AgNPs and the membrane surface. In this study, a substrate-independent method is reported to immobilize silver nanoparticles on polymeric membrane surfaces by firstly modifying the membrane surface with functional groups and then forming silver nanoparticles in situ. The obtained membranes had good anti-biofouling properties as demonstrated from disk diffusion and anti-biofouling tests. The silver nanoparticles were stably immobilized on the membrane surfaces and easily regenerated. This method is applicable to various polymeric micro-, ultra-, nano-filtration and reverse osmosis (RO) membranes.

Salicylazine activated plasmonic silver nanoprisms for identification of Fe(ii) and Fe(iii) from aqueous solutions

Silver nanoprisms were synthesized using salicylazine as a reducing and capping agent and were used to identify Fe2+/Fe3+ from a few real samples.

Green synthesis of silver nanoparticles using canthaxanthin from Dietzia maris AURCCBT01 and their cytotoxic properties against human keratinocyte cell line

AIM

Nano-biotechnologically synthesizing silver nanoparticles via canthaxanthin pigment extracted from Dietzia maris AURCCBT01 and assessing their cytotoxic therapeutic potential against human keratinocyte cell line (HaCaT) were the key objectives of this study.

METHODS AND RESULTS

The pigment extracted from D. maris AURCCBT01 was identified as canthaxanthin using UV-VIS spectroscopy, FTIR, NMR (¹ H NMR and ¹³ C NMR) and MS. Canthaxanthin, treated with silver nitrate solution, produced canthaxanthin-mediated silver nanoparticles and they were characterized by UV-VIS spectroscopy, FTIR, XRD, FESEM-EDX and TEM-SAED techniques. UV-VIS spectroscopy pointed out an absorption band at 420 nm, relating to the surface plasmon resonance of silver nanoparticles. FTIR findings suggested that the diverse functional groups of canthaxanthin bio-molecules played a significant task in capping the silver nanoparticles. XRD analysis exhibited 40·20 nm for the crystal size of nanoparticles. FESEM and TEM exhibited that the biosynthesized silver nanoparticles were spherical in shape with crystalline nature and the particle size was 40-50 nm. Moreover, the cytotoxicity assessment of the synthesized nanoparticles in HaCaT revealed significant cytotoxicity in the cultured cells with an IC₅₀ value of 43 µg ml^-1 .

CONCLUSION

Stable silver nanoparticles synthesized using canthaxanthin from D. maris AURCCBT01 were found effective for application in wound healing activity.

SIGNIFICANCE AND IMPACT OF THE STUDY

Biosynthesized silver nanoparticles via canthaxanthin bacterial pigment exhibited their cytotoxicity effect in HaCaT and testified their eventual therapeutic potential in the wound healing activity with no side effects in a cost effective and eco-friendly process.

Synthesis of 3D Dendritic Gold Nanostructures Assisted by a Templated Growth Process: Application to the Detection of Traces of Molecules

Complex architectures like 3D gold dendritic nanostructures were synthesized by an in situ templated growth method using a thin film of a block copolymer [polystyrene-b-poly(4-vinylpyridine)] deposited onto silicon substrates. The overall study has demonstrated the strong link between the morphology, size, and distribution of the structures and the synthetic physicochemical parameters, such as pH, reaction temperature, concentration, and nature of reactants. A nonequilibirum state of the medium has been required to create a fractal growth of the gold structures onto a prepatterned gold-seeded surface and has led to a better control of the structures' surface coverage rate. Those as-prepared nanodendrites have also exhibited high electrocatalytic activity toward a significant enhancement factor, as well as important sensitivity, thanks to tip effects. The electrochemical experiment results have demonstrated efficient adsorption and quantification of very low traces of specific molecules like glutathione or hexadecanethiol.

Synthesis and Antibacterial Activity of (AgCl, Ag)NPs/Diatomite Hybrid Composite

. In the present research, hybrid (AgCl, Ag)NPs/diatomite composites were synthesized by direct impregnation with aqueous silver nitrate solutions. The silver chloride nanoparticles (AgCl-NPs) were formed as an effect of the exchange reaction when silver interacted with the diatomite mineral impurity halite. Nanoparticles of metallic silver (AgNPs) were created by the reduction of silver ions under the influence of hydrogen peroxide. The content of silver chloride nanoparticles in the (AgCl, Ag)NPs/diatomite composite was limited by the content of the halite in the used diatomite. Samples of natural diatomite and synthesized (AgCl, Ag)NPs/diatomite composites were examined by using scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, infrared spectroscopy and thermogravimetric analysis. Moreover, the antibacterial potential of synthesized composites was also studied using the MIC (minimal inhibitory concentration) method against the most common drug-resistant microorganisms in the medical field: Gram-positive Staphylococcus aureus and Gram-negative Klebsiella pneumoniae. The obtained hybrid (AgCl, AgNPs)/diatomite composites were shown to have antimicrobial potential. However, widespread use requires further study by using various microorganisms and additional cytotoxic studies on eukaryotic systems, e.g., cell lines and animal models.

Following the Formation of Silver Nanoparticles Using In Situ X-ray Absorption Spectroscopy

The formation of silver and Au@Ag core@shell nanoparticles via reduction of AgNO₃ by trisodium citrate was followed using in situ X-ray absorption near-edge structure (XANES) spectroscopy and time-resolved UV-visible (UV-vis) spectroscopy. The XANES data were analyzed through linear combination fitting, and the reaction kinetics were found to be consistent with first-order behavior with respect to silver cations. For the Au@Ag nanoparticles, the UV-vis data of a lab-scale reaction showed a gradual shift in dominance between the gold- and silver-localized surface plasmon absorbance bands. Notably, throughout much of the reaction, distinct gold and silver contributions to the UV-vis spectra were observed; however, in the final product, the contributions were not distinct.

Silver nanoparticle probe for colorimetric detection of aminoglycoside antibiotics: picomolar-level sensitivity toward streptomycin in water, serum, and milk samples

BACKGROUND

The low cost of aminoglycoside (AMG) antibiotics facilitates their excessive use in animal husbandry and the agriculture sector. This scenario has led to the occurrence of residues in the food chain. After several years of AMG use in antibacterial therapy, resistance to streptomycin has begun to appear. Most of the detection methods developed for AMG antibiotics lacks specificity. A broad target specific nanoprobe would be ideal for detecting the entire class of AMGs. A rapid and sensitive method for the detection of AMGs is urgently needed.

RESULTS

Gallic acid-coated silver nanoparticles (AgNPs) were demonstrated as a nanoprobe for the colorimetric detection of AMGs (yellow to orange / red). A linear dynamic range of 50-650 pmol L^-1 was achieved readily by ratiometric spectrophotometry (A₅₆₀ /A₄₀₀ ) with a limit of detection (LOD) as low as 36 pmol L^-1 . The amine-groups of the AMGs function as molecular linkers, so that electrostatic coupling interactions between neighboring particles drive the formation of AgNP aggregates. The assay can also be applied for the determination of streptomycin residues in serum and milk samples.

CONCLUSION

This study revealed the potential of an AgNP probe for the rapid and cost-effective detection of low-molecular-weight target analytes, such as the AMGs. A ligand-induced aggregation of AgNPs coated with gallic acid was reported to be a rapid and sensitive assay for AMGs. Analysis of streptomycin was demonstrated with excellent picomolar-level sensitivity. Thus, the validated method can find practical applications in the ultrasensitive detection of AMGs in complex and diagnostic settings. © 2019 Society of Chemical Industry.

Biosynthesis of Silver Nanoparticles Mediated by Extracellular Pigment from Talaromyces purpurogenus and Their Biomedical Applications

In recent years, green syntheses have been researched comprehensively to develop inexpensive and eco-friendly approaches for the generation of nanoparticles. In this context, plant and microbial sources are being examined to discover potential reducing agents. This study aims to utilize an extracellular pigment produced by Talaromyces purpurogenus as a prospective reducing agent to synthesize silver nanoparticles (AgNPs). Biosynthesized AgNPs were characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), electron probe micro analyser (EPMA), and zeta potential. The pigment functional groups involved in the generation of AgNPs were investigated using Fourier transform infrared spectroscopy. TEM images showed that the generated nanoparticles were spherical, hexagonal, rod-shaped, and triangular-shaped with a particle size distribution from 4 to 41 nm and exhibited a surface plasmon resonance at around 410 nm. DLS and zeta potential studies revealed that the particles were polydispersed and stable (−24.8 mV). EPMA confirmed the presence of elemental silver in the samples. Biosynthesized AgNPs exhibited minimum inhibitory concentrations of 32 and 4 μg/mL against E. coli and S. epidermidis, respectively. Further, cytotoxicity of the AgNPs was investigated against human cervical cancer (HeLa), human liver cancer (HepG2), and human embryonic kidney (HEK-293) cell lines using 5-fluorouracil as a positive control. A significant activity was recorded against HepG2 cell line with a half-maximal inhibitory concentration of 11.1 μg/mL.

Characterization and study of the antibacterial mechanisms of silver nanoparticles prepared with microalgal exopolysaccharides

The green synthesis of biomaterials is of significant interest as it enables the safe and sustainable preparation of noble metallic nanoparticles for medical applications. Microalgae polysaccharides have received attention due to their outstanding properties such as biocompatibility, biodegradability and low cost. In addition, due to their variety of remarkable biological and physicochemical properties, polysaccharide-based nanoparticles have advantageous features yet to be explored. The primary objective of the current research was to investigate exopolysaccharides isolated from green microalgae Botryococcus braunii (EPBb) and Chlorella pyrenoidosa (EPCp), as both reducing and stabilizing agents, for the green synthesis of silver nanoparticles (AgNPs). Their antibacterial activity towards Gram-positive bacteria (Staphylococcus aureus), Gram-negative bacteria (Escherichia coli), and antibiotic-resistant bacteria (methicillin-resistant Staphylococcus aureus) was studied, as well as their cytotoxicity to human dermal fibroblasts. The presently synthesized AgNPs were spherical in shape and exhibited characteristic surface plasmon resonance at 430 nm. The main population had a particle size which ranged between 5 and 15 nm as analyzed by transmission electron micrographs. Zeta potentials averaged -51.81 ± 3.01 mV using EPBb and -12.16 ± 2.41 mV using EPCp. More importantly, AgNPs possessed strong antibacterial activity in a dose-dependent manner, even against drug-resistant bacteria. The enhanced antibacterial activity of these particles is explained due to extensive reactive oxygen species generation and bacterial cell membrane damage. In contrast, such AgNPs were not cytotoxic at the same therapeutic range to fibroblasts (0.5-10.0 μg/mL). In summary, these results showed that polysaccharide-capped AgNPs have a strong potential for numerous medical applications, such as antibacterial agents in pharmaceutical and biomedical areas.

The Preparation of Graphene Oxide-Silver Nanocomposites: the Effect of Silver Loads on Gram-Positive and Gram-Negative Antibacterial Activities

In this work, silver nanoparticles (Ag NPs) were decorated on thiol (–SH) grafted graphene oxide (GO) layers to investigate the antibacterial activities in Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (Pseudomonas aeruginosa). The quasi-spherical, nano-sized Ag NPs were attached to the GO surface layers, as confirmed by using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), respectively. The average size of GO-Ag nanocomposites was significantly reduced (327 nm) from those of pristine GO (962 nm) while the average size of loaded Ag NPs was significantly smaller than the Ag NPs without GO. Various concentrations of AgNO₃ solutions (0.1, 0.2, and 0.25 M) were loaded into GO nanosheets and resulted in the Ag contents of 31, 43, and 65%, respectively, with 1–2 nm sizes of Ag NPs anchored on the GO layers. These GO-Ag samples have negative surface charges but the GO-Ag 0.2 M sample (43% Ag) demonstrated the highest antibacterial efficiency. At 10 ppm load of GO-Ag suspension, only a GO-Ag 0.2 M sample yielded slight bacterial inhibition (5.79–7.82%). As the GO-Ag content was doubled to 20 ppm, the GO-Ag 0.2 M composite exhibited ~49% inhibition. When the GO-Ag 0.2 M composite level was raised to 100 ppm, almost 100% inhibition efficiencies were found on both Staphylococcus aureus (S.A.) and Pseudomonas aeruginosa (P.A.), which were significantly higher than using pristine GO (27% and 33% for S.A. and P.A.). The combined effect of GO and Ag nanoparticles demonstrate efficient antibacterial activities.

Special Resins for Stereolithography: In Situ Generation of Silver Nanoparticles

The limited availability of materials with special properties represents one of the main limitations to a wider application of polymer-based additive manufacturing technologies. Filled resins are usually not suitable for vat photo-polymerization techniques such as stereolithography (SLA) or digital light processing (DLP) due to a strong increment of viscosity derived from the presence of rigid particles within the reactive suspension. In the present paper, the possibility to in situ generate silver nanoparticles (AgNPs) starting from a homogeneous liquid system containing a well dispersed silver salt, which is subsequently reduced to metallic silver during stereolithographic process, is reported. The simultaneous photo-induced cross-linking of the acrylic resin produces a filled thermoset resin with thermal-mechanical properties significantly enhanced with respect to the unfilled resin, even at very low AgNPs concentrations. With this approach, the use of silver salts having carbon-carbon double bonds, such as silver acrylate and silver methacrylate, allows the formation of a nanocomposite structure in which the release of by-products is minimized due to the active role of all the reactive components in the three dimensional (3D)-printing processes. The synergy, between this nano-technology and the geometrical freedom offered by SLA, could open up a wide spectrum of potential applications for such a material, for example in the field of food packaging and medical and healthcare sectors, considering the well-known antimicrobial effects of silver nanoparticles.

Synergistic effects of plasmon induced Ag@Ag3VO4/ZnCr LDH ternary heterostructures towards visible light responsive O2 evolution and phenol oxidation reactions

The SPR effect of monodisperse Ag nanoparticles in Ag@Ag₃VO₄/ZnCr LDH heterostructures exhibits high photocatalytic activity towards evolution of O₂ and oxidation of phenol.

Enhancing the antimicrobial and antibiofilm effectiveness of silver nanoparticles prepared by green synthesis

Water soluble catechin oligomers produce small (8.5 nm) silver nanoparticles with high antimicrobial and antibiofilm efficacy.

Silver particle-loaded nickel oxide nanosheet arrays on nickel foam as advanced binder-free electrodes for aqueous asymmetric supercapacitors

Ag particle-loaded NiO nanosheet arrays promise rapid ion and electron transport, large electroactive surface area, and great structural stability.

Symmetry Breaking by Surface Blocking: Synthesis of Bimorphic Silver Nanoparticles, Nanoscale Fishes and Apples

A powerful approach to augment the diversity of well-defined metal nanoparticle (MNP) morphologies, essential for MNP advanced applications, is symmetry breaking combined with seeded growth. Utilizing this approach enabled the formation of bimorphic silver nanoparticles (bi-AgNPs) consisting of two shapes linked by one regrowth point. Bi-AgNPs were formed by using an adsorbing polymer, poly(acrylic acid), PAA, to block the surface of a decahedral AgNP seed and restricting growth of new silver to a single nucleation point. First, we have realized 2-D growth of platelets attached to decahedra producing nanoscale shapes reminiscent of apples, fishes, mushrooms and kites. 1-D bimorphic growth of rods (with chloride) and 3-D bimorphic growth of cubes and bipyramids (with bromide) were achieved by using halides to induce preferential (100) stabilization over (111) of platelets. Furthermore, the universality of the formation of bimorphic nanoparticles was demonstrated by using different seeds. Bi-AgNPs exhibit strong SERS enhancement due to regular cavities at the necks. Overall, the reported approach to symmetry breaking and bimorphic nanoparticle growth offers a powerful methodology for nanoscale shape design.

New Synthesis of Gold- and Silver-Based Nano-Tetracycline Composites

A new synthetic methodology of water-soluble gold and silver nanoparticles (AuNPs@TC and AgNPs@TC), using the antibiotic tetracycline (TC) as co-reducing and stabilizing agent, is reported. Both colloids exhibit high water stability. The average sizes obtained were 25±10 and 15±5 nm, respectively. Both composites were tested against TC-resistant bacteria, presenting an increasing antibacterial effect in the case of AgNPs@TC. The sensing towards metal ions was also explored. An interesting and reversible affinity of AuNPs@TC towards AlIII cations in an aqueous system was also observed.

Evolution of silver nanoparticles in the rat lung investigated by X-ray absorption spectroscopy

Following a 6-h inhalation exposure to aerosolized 20 and 110 nm diameter silver nanoparticles, lung tissues from rats were investigated with X-ray absorption spectroscopy, which can identify the chemical state of silver species. Lung tissues were processed immediately after sacrifice of the animals at 0, 1, 3, and 7 days post exposure and the samples were stored in an inert and low-temperature environment until measured. We found that it is critical to follow a proper processing, storage and measurement protocol; otherwise only silver oxides are detected after inhalation even for the larger nanoparticles. The results of X-ray absorption spectroscopy measurements taken in air at 85 K suggest that the dominating silver species in all the postexposure lung tissues were metallic silver, not silver oxide, or solvated silver cations. The results further indicate that the silver nanoparticles in the tissues were transformed from the original nanoparticles to other forms of metallic silver nanomaterials and the rate of this transformation depended on the size of the original nanoparticles. We found that 20 nm diameter silver nanoparticles were significantly modified after aerosolization and 6-h inhalation/deposition, whereas larger, 110 nm diameter nanoparticles were largely unchanged. Over the seven-day postexposure period the smaller 20 nm silver nanoparticles underwent less change in the lung tissue than the larger 110 nm silver nanoparticles. In contrast, silica-coated gold nanoparticles did not undergo any modification processes and remained as the initial nanoparticles throughout the 7-day study period.

Controlled synthesis of monodisperse silver nanoparticles supported layered double hydroxide catalyst

Monodisperse silver nanoparticles supported layered double hydroxides (Ag NPs–LDH) were preferentially deposited on the outer surfaces of pillared LDH offered a high catalytic activity on alcohol oxidation.

High-resolution insights into the early stages of silver nucleation and growth

Nucleation and growth of silver nanoparticles has already been investigated with various experimental and computational tools. However, owing to inherent problems associated with the analytical characterization of nucleation processes, there is a general lack of experimental data regarding the earliest precursors and smallest Ag(0) clusters. Here, we address this problem by the application of Synthetic Boundary Crystallization Ultracentrifugation, utilizing a multiwavelength detector for the first time, complemented by a specialized titration assay. These techniques shed new light on silver nanoparticle precursors existing in the pre-nucleation regime, and the initially nucleated ensemble of nanoclusters. For the first time, we present experimental data of UV-Vis spectra for fractionated silver clusters. These allow for unsurpassed insights into the sequence of nucleation and early growth species as well as their optical properties.

Formation and characterization of silver nanoparticles in aqueous solution via ultrasonic irradiation

In this study, a simple and green method to synthesize silver nanoparticles (Ag NPs) in aqueous solution via ultrasonic irradiation has been developed. Ultrafine Ag NPs with average diameter of 8 nm were obtained through sonicating aqueous solution of sodium hydroxide (NaOH, 0.1 mM) with adding silver nitrate solution (AgNO3, 5.88 mM) drop by drop. In pure aqueous solution, the reactive route related to hydroxyl radicals (OH) is presented. Furthermore, in alkaline aqueous solution, the effects of hydroxyl ions (OH(-)) on formation of Ag NPs are discussed detailedly. The formation of Ag NPs was tracked by surface plasmon resonance (SPR) band of ultraviolet-visible (UV-Vis) spectrum; the morphology of the obtained Ag NPs was characterized through transmission electron microscopy (TEM); energy dispersive X-ray spectroscopy (EDX) and X-ray powder diffraction (XRD) confirmed the formation of metallic Ag NPs.

Transformation of four silver/silver chloride nanoparticles during anaerobic treatment of wastewater and post-processing of sewage sludge

The increasing use of silver (Ag) nanoparticles [containing either elemental Ag (Ag-NPs) or AgCl (AgCl-NPs)] in commercial products such as textiles will most likely result in these materials reaching wastewater treatment plants. Previous studies indicate that a conversion of Ag-NPs to Ag2S is to be expected during wastewater transport/treatment. However, the influence of surface functionality, the nature of the core structure and the effect of post-processing on Ag speciation in sewage sludge/biosolids has not been investigated. This study aims at closing these knowledge gaps using bench scale anaerobic digesters spiked with Ag nitrate, three different types of Ag-NPs, and AgCl-NPs at environmentally realistic concentrations. The results indicate that neither surface functionality nor the different compositions of the NP prevented the formation of Ag2S. Silver sulfides, unlike the sulfides of other metals present in sewage sludge, were stable over a six month period simulating composting/stockpiling.