Spherical AgNPs Research Articles

Surface‐enhanced Raman scattering study of PP/Ag nanocomposite developed to prevent postsurgery infection

AbstractWide varieties of antibacterial medical materials coated with silver nanoparticles (AgNPs) are developed. However, studies about coating surgical are scare. Stable coated polypropylene (PP) surgical suture with spherical AgNPs (PP/Ag nanocomposite) was prepared using an optimized aqueous dipping method. Homogenous and linear distribution of AgNPs on the PP surface was verified by scanning electron microscope and atomic force microscopy combined to the bright field image. Quantitative analyses of the silver content were measured by inductively coupled plasma atomic emission spectroscopy and showed a grafting rate of 8 × 10−4%. Surface‐enhanced Raman scattering investigations confirmed the grafting of AgNPs on the surface of surgical suture and highlighted the regioselective adsorption of polyvinylpyrrolidone on the AgNPs via the AgO interactions. Finally, PP/Ag nanocomposite has shown a good stability in biological medium (saline solution NaCl 0.9%) and prominent biocompatibility against human umbilical vein endothelial cells. Antibacterial performances of PP/Ag nanocomposite against gram‐positive and gram‐negative colonies of bacteria were also investigated.

Aqueous leaf extracts of Cnidoscolus chayamansa (Mayan chaya) cultivated in Yucatán México. Part II: Uses for the phytomediated synthesis of silver nanoparticles

HypothesisRecently proposed alternatives for synthesizing silver nanoparticles involve the use of extracellular extracts of different plants in which the obtained particles show similar or improved characteristics with respect to particles obtained using more conventional methods. On this basis, this paper proposes the synthesis of nanoparticles (NPs) of silver (AgNPs) using aqueous extracts from the leaves of Cnidoscolus chayamansa McVaugh (Mayan chaya or tree spinach). ExperimentTen aqueous extracts from chaya leaves were prepared, varying the proportion of the mass in the extracts (% m/V): 0.1%, 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, 6.5%, 7.5% and 10.0%. Each of the extracts was used as a reducing agent in the green synthesis of AgNPs, using silver nitrate as a precursor salt at an initial concentration of 1.34 mM. The synthesized particles were characterized by UV–Vis spectroscopy, scanning electron microscopy, dynamic light dispersion (DLS), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. FindingThe non-purified silver particles synthesized with the aqueous chaya extracts were larger than 100 nm. When the extract concentration was increased particles with a different size and shape were obtained, due to variations in the antioxidant capacity of the different extracts. Starting with the 2.0% extract, agglomerated silver particles organized in a cauliflower shape were obtained, with an average size between 264.5 ± 2.42 and 4610 ± 17 nm. After the silver particles were purified, in all cases spherical AgNPs measuring <50 nm were obtained.

Cellulose hybrid nanocomposites using Napier grass fibers with in situ generated silver nanoparticles as fillers for antibacterial applications

Initially silver nanoparticles (AgNPs) were in situ generated in Napier grass fibers (NGFs) and these nanocomposite NGFs were used as fillers (by 1 wt% to 5 wt%) in cellulose matrix to make hybrid nanocomposite films. The formation of in situ generated AgNPs on the surface of the NGFs was studied using scanning electron microscope (SEM), high resolution transmission electron microscope (HR-TEM), Energy dispersive X-ray spectroscope (EDX) and X-ray photoelectron spectroscope (XPS). The HR-TEM analysis indicated the presence of spherical AgNPs on the surface of the fillers with a size ranging from 10 to 100 nm but majority of them in the 11 to 20 nm range. The POM images indicated the randomly oriented fillers in the hybrid composite films. Though the inflection temperatures of the hybrid composites were lower than for the matrix (due to catalytic activity of the AgNPs), the residual weight for them was higher than that of the matrix. The tensile strength of the hybrid nanocomposites varied between 73 MPa and 40 MPa while their tensile modulus between 4350 MPa and 2580 MPa for various filler contents. The hybrid nanocomposite films showed good antibacterial activity against Gram negative (E. coli) and Gram positive (S. aureus) bacteria.

Anisotropic Snowman-Like Silver Nanoparticles Synthesized by Caesalpinia sappan Extract and In Vitro Antibacterial Activity.

Anisotropic snowman-like silver nanoparticles (AgNPs) were synthesized using the extract of Caesalpinia sappan heartwood as a reducing agent in the presence of cetyltrimethylammonium bromide. Two surface plasmon resonance bands of the orange solution were observed at 446 nm and 539 nm in UV-visible spectra. High-resolution X-ray diffraction analysis confirmed the face-centered cubic structure of the AgNPs. High-resolution transmission electron microscopy images clearly revealed snowman-like AgNPs with an average size of 34.36 ± 11.44 nm. The C-O functional group was most likely involved in the synthesis of the AgNPs, which was demonstrated by Fourier transform infrared spectra. Most interestingly, the snowman-like AgNPs exhibited higher antibacterial activity than the spherical AgNPs and the extract alone. Among the tested strains, the snowman-like AgNPs showed the highest activity against Staphylococcus aureus, with minimum inhibitory concentrations of 4.69 μg/mL for the extract and 0.443 μg/mL for the silver. The antibacterial activity of the snowman-like AgNPs increased 24-fold against S. aureus. These results strongly suggested that the snowman-like AgNPs synthesized from C. sappan extract have potential for treating infected disease caused by S. aureus when the antibacterial activity was combined from plant extract and AgNPs. To our knowledge, the present report is the first in which the snowman-like AgNPs synthesized using a plant extract as a reducing agent showed excellent In Vitro antibacterial activity.

Bio-inspired AgNPs, multilayers-reduced graphene oxide and graphite nanocomposite for electrochemical $$\hbox {H}_{2}{\hbox {O}}_{2}$$ H 2 O 2 sensing

A bio-mediated route for the synthesis of silver nanoparticles (AgNPs) is an area of interest in research of many scientists, and this work aims to study the electrocatalytic activity of these particles during electrochemical sensing of H\(_{2}\)O\(_{2 }\) in a phosphate buffer media. The composite electrodes were fabricated using nearly spherical AgNPs and reduced graphene oxide (rGO) with the graphite (99.999% purity) support made of graphite paste. Graphene oxide (GO) was first synthesized using the modified Hummers method followed by rGO synthesis by chemical reduction of GO. rGO is consisting of about nine layers of rGO sheets of a wrinkled surface morphology with an intensity ratio of D to G band (\(I_{D}/I_{G})\) of 1.17 and an interplanar d-spacing of 0.36 nm as evidenced by HRTEM micrograph. There was about 10 times increase in the cell current with the AgNPs-impregnated composite–electrode compared to without AgNPs impregnation, and an overpotential of \(\hbox {H}_{2}\hbox {O}_{2}\) reduction was found to be \(-\)1.373 V with a detection limit of 19.04 \(\upmu \)M and 95.3% electrode stability with the graphite–rGO–AgNPs composite electrode. A nafion membrane cast on the rGO–AgNPs prevented the leakage of this composite from the electrode surface. The interference of various electroactive compounds on the amperometric response of the graphite–rGO–AgNPs electrode was also investigated.

In-Liquid Plasma Process for Size- and Shape-Controlled Synthesis of Silver Nanoparticles by Controlling Gas Bubbles in Water.

Most methods controlling size and shape of metal nanoparticles are chemical methods, and little work has been done using only plasma methods. Size- and shape-controlled synthesis of silver nanoparticles (Ag NPs) is proposed based on adjusting the gas bubble formation produced between two silver electrodes. The application of a voltage waveform with three different pulse widths during a plasma process in water can generate different gas bubble formations. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) images of Ag NPs synthesized using three different bubble formations reveal that spherical Ag NPs are synthesized when very tiny bubbles are generated between two electrodes or when only the grounded electrode is enveloped with large gas bubbles, but Ag nanoplates are synthesized when both electrodes are completely enveloped with large gas bubbles.

Biomimetic Synthesis of Silver Nanoparticles for Preparing Preservative Solutions for Mandarins (Citrus DeliciosaTenore)

Mandarin (Citrus deliciosa Tenore) is one of the most important fruit crops grown in the Hue province, Vietnam, and has immense economic, health and cultural significance. However, mandarins are highly perishable and more susceptible to diseases compared to other citrus fruits. In the present study, biomimetic synthesis of silver nanoparticles (AgNPs) for preparing preservative solutions for mandarins was investigated. Spherical and nanometer-sized AgNPs that were prepared with the help of ultrasound wave induced a reaction between silver nitrate solution (AgNO30.02[Formula: see text]M) and the leaf extract of Centella asiatica. Spherical AgNPs were formed easily in the extract at an ambient temperature and their average size ranged from 3[Formula: see text]nm to 30[Formula: see text]nm. These AgNPs exhibited potent antifungal activity against Macrophoma theicola B1 fungi, which were isolated from mandarin peels collected from agricultural lands of rural villages of Thua Thien-Hue province in Vietnam. Thus, we are successful in preparing an AgNPs-containing preservative solution as a mandarin fruit-coating material to inhibit the growth of M. theicola B1 fungi. The coating of mandarin fruits with this preservative solution prolonged the storage life of the fruits from 9 to 35 days. On the 35th day, the preserved fruits maintained their natural color and ripening, whereas the control sample decayed with white fungus covering its skin after 9 days of storage. Thus, coating mandarins with this solution can be proposed as an additional treatment for increasing their postharvest quality. Additionally, it can be a solution for protection against fungal infection and physiological damage and controlling the decay of mandarins, thereby prolonging their shelf life.

Preparation and characterisation of silver nanoparticles in an aqueous suspension of TETA modified graphene oxide and their antibacterial activity

A simple method to prepare silver nanoparticles (AgNPs)/triethylenetetramine (TETA)-functionalised graphene oxide (TGO) nanomaterial via electrostatic self-assemble, exploring the structure and antimicrobial properties of the as-prepared AgNPs/TGO composite is presented. This composite was characterised by Fourier transform infrared spectra, UV–Vis, X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and transmission electron microscopy (TEM). TEM image suggested the formation of spherical AgNPs with a narrow size distribution at ∼ 30 nm. The nanocomposites showed high bactericidal activity against Escherichia coli bacteria and Staphylococcus aureus bacteria. This work provides a simple, scalable and environmentally friendly approach to the preparation of AgNPs/TGO nanocomposite with promising antibacterial properties, which could be used as an artificial biomedical material or wound healing.

Light emitting diode irradiation induced shape conversion of DNA-capped silver nanoparticles and their antioxidant and antibacterial activities

Due to size- and shape-dependent properties, a shape-controlled synthesis of silver nanoparticles (AgNPs) is one of the research challenging topics for their production and potential applications. This work reported the simple eco-friendly syntheses of different shaped AgNPs controlled by the plasmid DNA content and light emitting diodes (LEDs) irradiation. The synthesized AgNPs appeared as yellow, orange and green colloidal AgNPs, which transmission electron microscope (TEM) images revealed their different shapes; spherical AgNPs, a mixture of spherical and hexagonal AgNPs, and a mixture of spherical, hexagonal and corner-truncated triangle AgNPs, respectively. The average sizes of spherical, hexagonal and corner-truncated triangle AgNPs in the green colloidal solution were 12.32 ± 2.22, 23.03 ± 6.62 and 15.84 ± 4.31 nm, respectively. The analyses of X-ray diffraction, selected area electron diffraction and high-resolution TEM indicated the crystalline nature of the synthesized particles as the face-centred cubic silver. All synthesized AgNPs exhibited antioxidant activities similarly, whereas the yellow colloidal AgNPs exhibited the strongest antibacterial activity against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus as compared with the green and orange colloidal AgNPs.

Green Synthesis of Silver Nanoparticles Using Sapota Fruit Waste and Evaluation of Their Antimicrobial Activity

Green synthesis of spherical silver nanoparticles (AgNPs) by using sapota fruit pomace was carried out in the present study. The extraction procedure for sapota pomace and reaction conditions were simple and convenient to handle and straightforwardly optimized using UV–Visible spectroscopy. The generated AgNPs were characterized using Fourier-transform infrared spectroscopy (FTIR). The morphology and crystalline phase of the AgNPs were determined from X-ray diffraction (XRD) spectroscopy and transmission electron microscopy (TEM). The spherical AgNPs synthesized after reduction with sapota pomace extract were biphasic in nature and displayed a particle size of 8–16 nm with moderate stability (Zeta potential of − 13.41). AgNPs synthesized with sapota pomace extract showed good antibacterial properties against Gram-positive as well as Gram-negative microorganisms, comparable to reported literature. The results of this study promote a productive utilization of fruit waste for the synthesis of nanoparticles.

Green silver nanoparticles from novel Brassicaceae cultivars with enhanced antimicrobial potential than earlier reported Brassicaceae members

In the present study, we report perhaps for the first time the use of novel varieties of Brassica oleracea var. botrytis and Raphanus sativus as potential bioreductant, to synthesize highly stable silver nanoparticles (AgNPs, no aggregation observed for six months), which is a significant finding as plant extract-directed AgNPs are intrinsically unstable and tend to aggregate. The reduction of Ag+ to Ag0 nanostructures was confirmed using UVVis spectroscopy showing SPR spectra at 400–435 nm. Nanosight and transmission electron microscope (TEM) analysis showed monodisperse spherical AgNPs (4–18 nm). Fourier transform infrared spectroscopy (FTIR) analysis revealed that the polyphenolics and other secondary metabolites including glucosinolates in the aqueous extracts may act as reducing/capping agent for the nanoparticle synthesis. X-ray diffraction (XRD) confirmed the face centered cubic crystalline (fcc) structure of AgNPs. Controlled synthesis of AgNPs was achieved by varying experimental parameters (AgNO3 concentration, extract volume, pH and temperature). These AgNPs exhibited strong antibacterial activity at significantly lower concentration (5 ppm) against both Gram negative (Escherichia coli, Myroides, Psuedomonas aeruginosa) and Gram positive (Kocuria and Promicromonospora) bacteria. In the present study, the green AgNPs showed (10–30%) better antimicrobial efficacy than chemical AgNPs and AgNPs from other Brassicaceae members. These green AgNPs may have promising application in nano-drug formulation to combat bacterial infections, in future.

Microwave-assisted green synthesis and antimicrobial activity of silver nanoparticles derived from a supercritical carbon dioxide extract of the fresh aerial parts of &lt;i&gt;Phyllanthus niruri&lt;/i&gt; L

Purpose: To synthesize and evaluate the antimicrobial activity of silver nanoparticles (AgNPs) derived from a supercritical carbon dioxide extract of the fresh aerial parts of Phyllanthus niruri. Methods: The synthesis of AgNPs of a P. niruri extract was carried out in a microwave oven. The extraction was carried out using a supercritical fluid extractor. The AgNPs were characterized by the Ultraviolet-visible (UV-vis) spectral analysis, Dynamic Light Scattering (DLS) zetasizer analysis, Transmission electron microscopy (TEM), X-ray diffraction (XRD) analysis and Fourier transform infrared (FT-IR) spectroscopy. The antimicrobial assays of AgNPs were carried out against different bacterial and fungal strains. Results: Results of various analytical techniques confirmed the synthesis of AgNPs of a P. niruri extract. The UV–vis spectroscopy showed an intense silver surface plasmon resonance band at 415 NM. The AgNPs had a mean size of 110 nm in the Zetasizer analysis. TEM images illustrated spherical AgNPs having a mean particle size of 110 nm. The X-ray diffractograms showed peaks at 38.17°, 44.28°, and 64.52°. The average crystallite size of Ag-NPs was found to be 110 nm. FT-IR spectra confirmed the stability of the AgNPs. The AgNPs demonstrated good antimicrobial effects against several tested pathogenic microbes. Conclusion: An efficiently synthesized AgNPs of P. niruri (SC-CO2) extract has been prepared by a simple, eco-friendly, cost-effective, rapid green chemistry methodology. The AgNPs of P. niruri extract possesses significant antimicrobial properties against the tested bacterial and fungal strains. Keywords: Nanoparticles, Phyllanthus niruri, Supercritical fluid extraction, Microwave, Antimicrobial activity

Silver-pig skin nanocomposites and mesenchymal stem cells: suitable antibiofilm cellular dressings for wound healing

BackgroundTreatment of severe or chronic skin wounds is an important challenge facing medicine and a significant health care burden. Proper wound healing is often affected by bacterial infection; where biofilm formation is one of the main risks and particularly problematic because it confers protection to microorganisms against antibiotics. One avenue to prevent bacterial colonization of wounds is the use of silver nanoparticles (AgNPs); which have proved to be effective against non-multidrug-resistant and multidrug-resistant bacteria. In addition, the use of mesenchymal stem cells (MSC) is an excellent option to improve wound healing due to their capability for differentiation and release of relevant growth factors. Finally, radiosterilized pig skin (RPS) is a biomatrix successfully used as wound dressing to avoid massive water loss, which represents an excellent carrier to deliver MSC into wound beds. Together, AgNPs, RPS and MSC represent a potential dressing to control massive water loss, prevent bacterial infection and enhance skin regeneration; three essential processes for appropriate wound healing with minimum scaring.ResultsWe synthesized stable 10 nm-diameter spherical AgNPs that showed 21- and 16-fold increase in bacteria growth inhibition (in comparison to antibiotics) against clinical strains Staphylococcus aureus and Stenotrophomonas maltophilia, respectively. RPS samples were impregnated with different AgNPs suspensions to develop RPS-AgNPs nanocomposites with different AgNPs concentrations. Nanocomposites showed inhibition zones, in Kirby–Bauer assay, against both clinical bacteria tested. Nanocomposites also displayed antibiofilm properties against S. aureus and S. maltophilia from RPS samples impregnated with 250 and 1000 ppm AgNPs suspensions, respectively. MSC were isolated from adipose tissue and seeded on nanocomposites; cells survived on nanocomposites impregnated with up to 250 ppm AgNPs suspensions, showing 35% reduction in cell viability, in comparison to cells on RPS. Cells on nanocomposites proliferated with culture days, although the number of MSC on nanocomposites at 24 h of culture was lower than that on RPS.ConclusionsAgNPs with better bactericide activity than antibiotics were synthesized. RPS-AgNPs nanocomposites impregnated with 125 and 250 ppm AgNPs suspensions decreased bacterial growth, decreased biofilm formation and were permissive for survival and proliferation of MSC; constituting promising multi-functional dressings for successful treatment of skin wounds.

Controllable Synthesis of Silver Nanoparticles Using Three‐Phase Flow Pulsating Mixing Microfluidic Chip

On the basis of liquid‐phase reduction mechanism, a novel synthesis method to prepare silver nanoparticles (AgNPs) is proposed, which uses piezoelectric‐actuated three‐phase flow pulsating mixing microfluidic chip. In order to study and explore the influence of different factors on the synthesis of AgNPs, a series of related synthesis experiments were carried out. The corresponding experimental conditions include the concentration of sodium hydroxide and reducing agent solution, polyvinylpyrrolidone (PVP) dosage, inlet flow rate, and synthesis temperature. The synthesized AgNPs were characterized by the UV‐Vis absorption spectrophotometer and transmission electron microscopy. The effects of different experimental conditions on the controllable synthesis of AgNPs were analyzed, and the optimum synthesis conditions of AgNPs were obtained. Experimental results show that the spherical AgNPs with an average particle diameter of about 29 nm, high yield, fine morphology, and good monodispersity were synthesized using the microfluidic chip under the conditions of the working frequency (200 Hz), the initial concentration of silver nitrate (1 mM), the synthesis temperature (80°C), the concentration ratio of sodium hydroxide to silver nitrate (2 : 1), the concentration ratio of glucose to silver nitrate (4 : 1), the inlet flow rate (3.5 ml/min), and the quality ratio of PVP to silver (more than 1 : 1). The related research shows that it is an efficient synthesis method to develop the controllable synthesis experiments of AgNPs under multifactors using the three‐phase pulsating mixing microfluidic chip.

Surfactant mediated interaction of vancomycin with silver nanoparticles

In this present study, spherical AgNPs have been synthesized by chemical reduction method in the presence of different surfactants i.e. trisodium-citrate and polyvinylpyrrolidone. Further, these synthesised AgNPs have been functionalized with different concentrations of glycopeptide antibiotic (vancomycin). The interaction between AgNPs and antibiotic has been studied using various analytical techniques i.e. UV–vis absorption spectroscopy, Dynamic light scattering, and X-ray diffraction. Further, the nature of bonding between antibiotic and AgNPs has been probed by Fourier transform infrared spectroscopy, which shows the amine bonding between vancomycin and silver nanoparticles surface. The role of different nature of surfactants on attachment and interaction mechanism of drug with AgNPs has been studied.

Stable PEG-coated silver nanoparticles – A comprehensive toxicological profile

The present study was purported to assess the toxicological profile of bare and polyethylene glycol (PEG) coated spherical silver nanoparticles (AgNPs) by means of in vitro (on human keratinocytes – HaCat cells) and in vivo non-invasive tests (after intraperitoneal - i.p. administration to mice). Bare and PEG-coated AgNPs were synthesized by applying Turkevich's method slightly modified. The physico-chemical characterization revealed the formation of stable, spherical AgNPs and PEG-AgNPs, with narrow size distributions and mean hydrodynamic sizes in the range of 19 nm and 50 nm, respectively.Toxicity data revealed a dose-dependent safe profile for low concentrations of test compounds (<10 μM) in terms of cell viability, whereas higher concentrations were associated with a high rate of cell mortality. In vivo acute/subacute toxicity data showed no denotive changes in mice health status after i.p. administration. Histological observations of internal organs and the biochemical parameters analyzed together with the other biological observations showed a low toxicity level with no major differences related to control, albeit at skin level a reduced number of mast cells was detected. All these observations provide strong support for the idea that coated silver nanoparticles could be applied as targeted nanocarriers for skin pathologies and diagnostic.

Biomimetic synthesis of silver nanoparticles and evaluation of their catalytic activity towards degradation of methyl orange

This paper described the significant effect of process variables like reductant concentrations, substrate concentration, reaction pH and reaction temperature on the size, morphology and yield of the silver nanoparticles (AgNPs) synthesized using aqueous leaf extract of a medicinal plant Momordica charantia (Bitter guard). By means of UV–vis spectroscopy, XRD analysis, TEM analysis and Fluorescence analysis, it is observed that the reaction solution containing 10−3 M of AgNO3 of pH 5.3 + 10 ml of aqueous leaf extract at normal room temperature, was optimum for synthesis of stable, polydisperse, predominantly spherical AgNPs with average size of 12.15 nm. FT-IR and TEM studies confirmed the stability of AgNPs was due to the capping of phytoconstituents present in the leaf extract. The aqueous solution of leaf extract containing AgNPs showed remarkable catalytic activity towards degradation of methyl orange (MO) in aqueous medium.

Green synthesis of silver nanoparticles using transgenic Nicotiana tabacum callus culture expressing silicatein gene from marine sponge Latrunculia oparinae

In the present investigation, transgenic tobacco callus cultures and plants overexpressing the silicatein gene LoSilA1 from marine sponge Latrunculia oparinae were obtained and their bioreduction behaviour for the synthesis of silver nanoparticles (AgNPs) was studied. Synthesized nanoparticles were characterized using UV–visible spectroscopy, Fourier transformed infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic flame electron microscopy (AFM) and nanoparticle tracking analysis (NTA). Our measurements showed that the reduction of silver nitrate produced spherical AgNPs with diameters in the range of 12–80 nm. The results of XRD analysis proved the crystal nature of the obtained AgNPs. FTIR analysis indicated that particles are reduced and stabilized in solution by the capping agent, which is likely to be proteins present in the callus extract. Interestingly, the reduction potential of LoSiLA1-transgenic callus line was increased three-fold compared with the empty vector-transformed calli. The synthesized AgNPs were found to exhibit strong antibacterial activity against Escherichia coli and Agrobacterium rhizogenes. The present study reports the first evidence for using genetic engineering for activation of the reduction potential of plant cells for synthesis of biocidal AgNPs.

Physicochemical properties and cytotoxicity of cysteine-functionalized silver nanoparticles

The preparation of stable cysteine-capped silver nanoparticles (AgNPs), via the reduction of silver ions with sodium borohydride and modification of formed nanoparticles by l-cysteine, was developed. The micrographs from transmission electron microscopy (TEM) revealed that the spherical AgNPs exhibited an average size equal to 22±4nm. Surface enhanced Raman spectroscopy (SERS) and inductively coupled plasma optical emission spectrometry (ICP-OES) confirmed a chemisorption of cysteine molecules on the AgNPs. Additionally, dynamic light scattering (DLS) measurements showed that the AgNPs were stable for ionic strength lower than 5×10−3molL−1 and at 6.8<pH<4.5. The electrophoretic mobility measurements allowed to determine the isoelectric point of AgNPs, which appeared at pH 5.1. Below this value, the AgNPs were positively charged with the zeta potential equal to +68±3mV at pH 3.5. Under alkaline condition, the zeta potential of AgNPs was negative, attaining a value of −71±3mV at pH 9.5. The AgNPs were prone to the processes of oxidative dissolution, which was assessed using atomic absorption spectrometry (AAS). The cytotoxicity of AgNPs towards histiocytic lymphoma (U-937) and human promyelocytic (HL-60) cells was studied by the evaluation of changes in mitochondrial functions and cell membrane integrity. In the case of the HL-60 cells, apoptosis caused by the membrane damage was dominant. Furthermore, the obtained results showed the does-dependent impact of the AgNPs on the cell viability. Finally, it was found that the AgNP concentration of 15mgL−1 caused a complete destruction of cells of both types.

Biosynthesis of silver nanoparticles from the novel strain of Streptomyces Sp. BHUMBU-80 with highly efficient electroanalytical detection of hydrogen peroxide and antibacterial activity

The use of a microbial supernatant has become a potential source for the eco-friendly and rapid synthesis of nanoparticles. In this study, we have targeted to synthesize silver nanoparticles (AgNPs) using extracellular secretion of Streptomyces sp. The strain was successfully isolated from the soil samples and identified as Streptomyces sp. BHUMBU-80 on the basis of morphological, biochemical and Phylogenetic analysis. The synthesized AgNPs was characterized using several modern characterizing techniques such as UV-vis Spectroscopy, FTIR spectroscopy, SEM, EDX spectroscopy, TEM, XRD and XPS. The presence of characteristics SPR band at 450nm confirmed the synthesis of AgNPs. The FTIR spectra confirmed the involvement of various functional groups present in culture supernatant responsible for the reduction of Ag+ ions into Ag0. SEM and TEM analysis confirmed the presence of spherical AgNPs with an average size of 21±1nm. The XPS analysis confirmed the presence of two individual peaks which attributed to the Ag 3d3/2 and Ag 3d5/2 binding energies corresponding to the presence of metallic silver. The electrochemical studies of the green synthesized AgNPs using a glassy carbon electrode showed the superior electrocatalytic activity towards the reduction of H2O2. The calibration plot was established for H2O2 in the concentration range from 50μM to 1000μM with 50μM detection limit, at a signal-to-noise ratio of 3 in a three-electrode cell with a Pt plate as the counter electrode. Additionally, the AgNPs also showed potent antibacterial activity against pathogenic bacteria like E. coli, and S. aureus.