The antibacterial and anti-biofouling performance of biogenic silver nanoparticles by Lactobacillus fermentum

Biofouling is a major challenge in the water industry and public health. Silver nanoparticles (AgNPs) have excellent antimicrobial properties and are considered to be a promising anti-biofouling agent. A modified method was used to produce small sized and well-dispersed biogenic silver nanoparticles with a mean size of ~6?nm (Bio-Ag0-6) using Lactobacillus fermentum. The morphology, size distribution, zeta potential and oxidation state of the silver were systematically characterized. Determination of minimal inhibitory and bactericidal concentration results revealed that biogenic silver Bio-Ag^0-6 can effectively suppress the growth of the test bacteria. Additionally, the inhibition effects of Bio-Ag^0-6 on biofilm formation and on established biofilms were evaluated using P. aeruginosa (ATCC 27853) as the model bacterium. The results from microtiter plates and confocal laser scanning microscopy demonstrated that Bio-Ag^0-6 not only exhibited excellent antibacterial performance but also could control biofilm formation and induce detachment of the bulk of P. aeruginosa biofilms leaving a small residual matrix.     

Silver Nanoparticles for the Adsorption of Manganese from Biological Samples

In this study, silver nanoparticles were prepared and used for separation and preconcentration of manganese from biological samples. The technical feasibility of silver nanoparticles for manganese removal was investigated under batch studies. The effects of different parameters such as pH of solution, time (t), amounts of PAN (E), and silver nanoparticles (N) on the adsorption of manganese by silver nanoparticle were investigated using factorial design and response surface methodology based on Box–Behnken design. Thermodynamic parameters indicate the adsorption process to be exothermic. The limit of detection of the proposed method followed by inductively coupled plasma was found to be 0.08?µg L^?1. The method was applied to determine of manganese in biological samples.     

The antibacterial activity of biogenic silver and its mode of action

In a previous study, biogenic silver nanoparticles were produced by Lactobacillus fermentum which served as a matrix preventing aggregation. In this study the antibacterial activity of this biogenic silver was compared to ionic silver and chemically produced nanosilver. The minimal inhibitory concentration (MIC) was tested on Gram-positive and Gram-negative bacteria and was comparable for biogenic silver and ionic silver ranging from 12.5 to 50 mg/L. In contrast, chemically produced nanosilver had a much higher MIC of at least 500 mg/L, due to aggregation upon application. The minimal bactericidal concentration (MBC) in drinking water varied from 0.1 to 0.5 mg/L for biogenic silver and ionic silver, but for chemically produced nanosilver concentrations, up to 12.5 mg/L was needed. The presence of salts and organic matter decreased the antimicrobial activity of all types of silver resulting in a higher MBC and a slower inactivation of the bacteria. The mode of action of biogenic silver was mainly attributed to the release of silver ions due to the high concentration of free silver ions measured and the resemblance in performance between biogenic silver and ionic silver. Radical formation by biogenic silver and direct contact were found to contribute little to the antibacterial activity. In conclusion, biogenic nanosilver exhibited equal antimicrobial activity compared to ionic silver and can be a valuable alternative for chemically produced nanosilver.     

Eco-friendly synthesis of silver nanoparticles by Bacillus subtilis and their antibacterial activity

Bacillus subtilis was used for biogenic of silver nanoparticles. Characterization of the prepared silver nanoparticles was done by UV–Vis spectroscopy, Transmission Electron Microscopy (TEM), and Fourier Transform Infrared Spectroscopy (FT-IR). The particle size of the prepared nanoparticles ranges from 3 to 20 nm with spherical or roughly spherical forms. The antimicrobial efficacy of the produced nanoparticles was investigated against five strains of multidrug resistant microorganisms including: Staphylococcus aureus (MRSA), Staphylococcus epidermidis, Klebsiella. pneumoniae, Escherichia coli and Candida albicans tested as yeast. During this study, the minimum inhibitory concentrations (MICs) and the minimum lethal concentrations (MLCs) of synthesized silver nanoparticles were detected using selected strains of the genus Bacillus by a broth dilution method. The rate of MIC of the prepared silver nano-particles versus the investigated clinical isolates exhibit a massive anti-microbial efficacy; (230 µgml⁻¹) for MRSA; 180 for Staphylococcus epidermidis, 200 for Escherichia coli and 100 µgml⁻¹ for Candida albicans. On the other hand, the lowest anti-microbial efficacy (300 µgml⁻¹) was appeared for Klebsiella pneumonia. The obtained results demonstrated the effectiveness of the biogenic nanoparticles and the possibility of using them as a new method in combating infectious diseases.     

Optical ascorbic acid sensor based on the fluorescence quenching of silver nanoparticles

A sensitive and selective fluorimetric sensor for the assay of ascorbic acid (AA) using silver nanoparticles as emission reagent was investigated. In this study, silver nanoparticles were prepared based on aqueous–gaseous phase reaction of silver nitrate solution and ammonia gas. The nanoparticles were water‐soluble, stable and had a narrow emission band. They were used as a fluorescence probe for the assay of ascorbic acid on its quenching effect on the emission of silver nanoparticles. The principal reason for quenching is likely to be a complexation between ascorbic acid and silver nanoparticles. The quenching mechanism was established by Stern–Volmer law. Under the optimum conditions, the quenched fluorescence intensity was linear with the concentration of ascorbic acid in the range of 4.1 × 10^?6 to 1.0 ×10^?4 m (r = 0.9985) with a detection limit of 1.0 × 10^?7 m . The RSD for repeatability of the sensor for the assay of ascorbic acid concentration of 3.0 × 10^?5 and 4.0 × 10^?6 m was found to be 1.5 and 1.3%, respectively. The proposed method was applied to the determination of ascorbic acid in vegetables and vitamin C tablets. Copyright © 2009 John Wiley & Sons, Ltd.     

Formation of Nanoscale Elemental Silver Particles via Enzymatic Reduction by Geobacter sulfurreducens

Geobacter sulfurreducens reduced Ag(I) (as insoluble AgCl or Ag⁺ ions), via a mechanism involving c-type cytochromes, precipitating extracellular nanoscale Ag(0). These results extend the range of metals known to be reduced by Geobacter species and offer a method for recovering silver from contaminated water as potentially useful silver nanoparticles.     

Antifungal and physical characteristics of modified denture base acrylic incorporated with silver nanoparticles

doi: 10.1111/j.1741‐2358.2011.00489.x Antifungal and physical characteristics of modified denture base acrylic incorporated with silver nanoparticles Objective: This study evaluated the antifungal and physical characteristics of denture base acrylic combined with silver nanoparticles. Materials and methods: Polymerized denture acrylic disc specimens containing 0 (control), 1.0, 5.0, 10.0, 20.0 and 30.0 wt% of silver nanoparticles were placed on separate culture plate dish and 100 ìL samples of yeast suspension of Candida albicans strain were inoculated on each specimens and incubated at 37°C, for 24 h. The antifungal effects were evaluated as a number of viable cells in retrieved fungal suspension. To characterize physical aspects, specimens were tested for elution of silver cation (Ag⁺) at 24 h and 30th day, thermal analysis (TG/DTA), scanning electron microscope and energy dispersed X‐ray analysis (SEM/EDX) and color stability. Results: Significant reduced CFU was exhibited at 20.0 and 30.0 wt% of silver nanoparticles incorporated (p < 0.01) and Ag⁺ elution from specimens (maximum 0.356 ± 0.11 mg/L) contributed little to the antifungal activity considering MIC of Ag⁺ in this study (3.0 mg/L). The successful synthesis of modified denture acrylic containing silver nanoparticles was accessed by TG/DTA and EDX analysis. Conclusion: The modified denture base acrylic combined with silver nanoparticles displayed antifungal properties and acted like latent antifungal material itself with low‐releasing Ag⁺, however, the improvement of poor color stability was still required.     

Investigating the parameters affecting the adsorption of amino acids onto AgCl nanoparticles with different surface charges

In this paper, adsorption behaviors of typical neutral (alanine), acidic (glutamic acid) and basic (lysine) amino acids onto the surfaces of neutral as well as positively and negatively charged silver chloride nanoparticles were examined. Silver chloride nanoparticles with different charges and different water content were synthesized by reverse micelle method. The adsorptions of the above mentioned amino acids onto the surfaces of differently charged silver chloride nanoparticles were found to depend strongly on various parameters including pH of the aqueous solution, type of amino acid, water to surfactant mole ratio, and type of charges on the surfaces of silver chloride nanoparticles. It was found that the interaction of –NH₃ ⁺ groups of the amino acids with silver ion could be a driving force for adsorption of amino acids. Alanine and Glutamic acid showed almost similar trend for being adsorbed on the surface of silver chloride nanoparticles. Electrostatic interaction, hydrophobicity of both nanoparticle and amino acid, complex formation between amine group and silver ion, interaction between protonated amine and silver ion as well as the number of nanoparticles per unit volume of solution were considered for interpreting the observed results.     

Label-free capacitive immunosensor for microcystin-LR using self-assembled thiourea monolayer incorporated with Ag nanoparticles on gold electrode

A label-free immunosensor based on a modified gold electrode incorporated with silver (Ag) nanoparticles (NPs) to enhance the capacitive response to microcystin-LR (MCLR) has been developed. Anti-microcystin-LR (anti-MCLR) was immobilized on silver nanoparticles bound to a self-assembled thiourea monolayer. Interaction of anti-MCLR and MCLR were directly detected by capacitance measurement. Under optimum conditions, MCLR could be determined with a detection limit of 7.0pgl(-1) and linearity between 10pgl(-1) and 1mugl(-1). The immobilized anti-MCLR on self-assembled thiourea monolayer incorporated with silver nanoparticles was stable and good reproducibility of the signal could be obtained up to 43 times with an R.S.D. of 2.1%. Comparing to the modified electrode without silver nanoparticles it gave 1.7-fold higher sensitivity and lower limit of detection. The developed immunosensor was applied to analyze MCLR in water samples and the results were in good agreement with those obtained by high-performance liquid chromatography (HPLC) (P<0.05).     

Biosynthesis of silver nanoparticles using Penicillium verrucosum and analysis of their antifungal activity

The present study describes the biosynthesis of silver nanoparticles, using the fungus Penicillium verrucosum. The silver nanoparticles were synthesised by reacting silver nitrate (AgNO₃) with the cell free filtrates of the fungal culture, and were then characterized by UV–visible spectroscopy, transmission electron microscopy, scanning electron microscopy, energy-dispersive, and X-ray diffraction analysis to further evaluate their successful biosynthesis, optical and morphological features (size and shape), and crystallinity. The bioactivity of the synthesized nanoparticles against two phytopathogenic fungi i.e: Fusarium chlamydosporum and Aspergillus flavus was evaluated using nanomaterial seeding media. These biogenic silver nanoparticles were polydisperse in nature, with a size of 10–12 nm. With regard to the antifungal activity, 150 ppm of the nanoparticles suppressed the growth of F. chlamydosporum and A. flavus by about 50%. To the best of our knowledge, this is the first report on the use of P. verrucosum to synthesise silver nanoparticles. The present study demonstrates a novel, simple, and eco-friendly process for the generation of biofunctionally useful biogenic nanoparticles.     

Silver Nanoparticles as a New Solid-Phase Adsorbent and Its Application to Preconcentration and Determination of Lead from Biological Samples

A new, simple, and fast method for preconcentration and determination of trace amount of lead from biological samples was developed by modified silver nanoparticle-based solid-phase extraction technique and graphite furnace atomic absorption spectrometry. In this study, morin was used as a complexing agent. Some factors influencing the recovery of lead including pH, sample flow rate, type, flow rate, and least amount of the eluent for elution of the lead from silver nanoparticles were studied and optimized. Under the optimum conditions, the detection limit of this method was 68 ng L⁻¹, and the relative standard deviation was 4.1% (n = 10, c = 20 μg L⁻¹). The developed procedure was validated by the analysis of certified reference material and applied to the recovery and determination of lead in biological samples.     

Mycosynthesis and characterization of silver nanoparticles and their activity against some human pathogenic bacteria

The aim of this study was to biosynthesis silver nanoparticles from the fungus Nigrospora sphaerica isolated from soil samples and to examine their activity against five human pathogenic strains of bacteria viz. Escherichia coli, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella typhi and Staphylococcus aureus using disc diffusion method. The synergistic effect of silver nanoparticles in combination with commonly used antibiotic Gentamycin against the selected bacteria was also examined. The synthesized silver nanoparticles from free-cell filtrate were characterized by using UV–Vis spectrophotometer analysis, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). UV–Vis spectrophotometer analysis showed a peak at 420 nm indicating the synthesis of silver nanoparticles, FTIR analysis verified the detection of protein capping of silver nanoparticles while SEM micrographs revealed that the silver nanoparticles are dispersed and aggregated and mostly having spherical shape within the size range between 20 and 70 nm. The synthesized silver nanoparticles exhibited a varied growth inhibition activity (15–26 mm diam inhibition zones) against the tested pathogenic bacteria. A remarkable increase of bacterial growth inhibition (26–34 mm diam) was detected when a combination of silver nanoparticles and Gentamycin was used. A significant increase in fold area of antibacterial activity was observed when AgNPs in combination with Gentamycin was applied. The synthesized silver nanoparticles produced by the fungus N. sphaerica is a promising to be used as safe drug in medical therapy due to their broad spectrum against pathogenic bacteria.     

Synthesis of Silver Nanoparticles Using Callus Extract of Carica papaya — A First Report

This is the first report of synthesis of silver nanoparticles by using callus extract of Carica papaya. MS medium supplemented with the growth hormones, 2.0 mg l^?1 IBA and 0.5 mg l^?1 BAP was found to be more suitable for the induction of callus and multiple shoots in papaya. The extract of callus obtained by grinding showed ability of synthesis of silver nanoparticles when treated with silver nitrate (1 mM). The formation of brown colour in the reaction mixture indicates the synthesis of silver nanoparticles. The further detection and characterization of these synthesized silver nanoparticles was carried by spectrophotometry. FTIR spectrum analysis showed peaks between 1000–2000 cm^?1 which confirmed the presence of proteins and other ligands required for the synthesis and stabilization of silver nanoparticles. SEM micrograph confirmed the synthesis of spherical silver nanoparticles in the size range of 60–80 nm.     

Aqueous extract of gum olibanum (Boswellia serrata): A reductant and stabilizer for the biosynthesis of antibacterial silver nanoparticles

A simple and ecofriendly biosynthetic process has been developed for silver nanoparticles using the aqueous extract of gum olibanum (Boswellia serrata), a renewable natural plant biopolymer. The water soluble compounds in the gum serve as dual functional reducing and stabilizing agents. The effect of concentration of gum and silver nitrate; and reaction time on nanoparticle synthesis was studied. The UV–visible spectroscopy, transmission electron microscopy and X-ray diffraction techniques were used to characterize the synthesized nanoparticles. By tuning the reaction conditions, size controlled spherical nanoparticles of around 7.5 ± 3.8 nm was achieved. Using Fourier transform infrared spectroscopy and Raman spectroscopy, a probable mechanism involved in reduction and stabilization of nanoparticles has been explained. The produced silver nanoparticles exhibited substantial antibacterial activity on both the Gram classes of bacteria. By virtue of being biogenic and encapsulated with proteins, these surface functionalized nanoparticles can be easily integrated for various biological applications.     

Application of Factorial Design and Box–Behnken Matrix in the Optimization of a Magnetic Nanoparticles Procedure for Copper Determination in Water and Biological Samples

This study describes the development by response surface methodology (RSM) of a procedure for copper determination by inductively coupled plasma optical emission spectrometry (ICP-OES) in water and biological samples after extraction by magnetic nanoparticles. Four variables such as, pH of solution, amount of extractant, amount of nanoparticles, and time were regarded as factors in the optimization study. Results of the two-level full factorial design (2⁴) based on an analysis of variance demonstrated that only the pH, amount of extractant (E), and amount of nanoparticles (N) were statistically significant. Optimal conditions for the extraction of copper samples were obtained by using Box–Behnken design. Optimum conditions were 5.1, 7.2 mg, and 9.6 mg, for pH of solution, amount of nanoparticles, and amount of extractant, respectively. Under the optimized experimental conditions, the detection limit of the proposed method followed by ICP-OES was found to be 0.9?µg L^?1. The method was applied to the determination of copper in water and biological samples.     

Pomegranate peel induced biogenic synthesis of silver nanoparticles and their multifaceted potential against intracellular pathogen and cancer

In the field of nano-biotechnology, silver nanoparticles (AgNPs) share a status of high repute owing to their remarkable medicinal values. Biological synthesis of environment-friendly AgNPs using plant extracts has emerged as the beneficial alternative approach to chemical synthesis. In the current study, we have synthesized biogenic silver nanoparticles (PG-AgNPs) using the peel extract of Punica granatum as a reducing and stabilizing agent. The as-synthesized PG-AgNPs were characterized and evaluated for their antibacterial and anticancer potential. UV–Visible spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS) confirmed the formation of biogenic PG-AgNPs. The antibacterial potential was assessed against the biofilm of Listeria monocytogenes. The PG-AgNPs were efficacious against sessile bacteria and their biofilm as well. The as-synthesized nanoparticles at sub-MIC values showed dose-dependent inhibition of biofilm formation. Corroborating results were observed under crystal violet assay, Congo red staining, Confocal microscopy and SEM analysis. The anticancer ability of the nanoparticles was evaluated against MDA-MB-231 metastatic breast cancer cells. As evident from the MTT results, PG-AgNPs significantly reduced the cell viability in a dose-dependent manner. Exposure of MDA-MB-231 cells led to the accumulation of reactive oxygen species (ROS). Morphological changes and DNA fragmentation showed the strong positive effect of PG-AgNPs on the induction of apoptosis. Collectively, the as-synthesized PG-AgNPs evolved with synergistically emerged attributes that were effective against L. monocytogenes and also inhibited its biofilm formation; moreover, the system displayed lower cytotoxic manifestation towards mammalian cells. In addition, the PG-AgNPs embodies intriguing anticancer potential against metastatic breast cancer cells.     

Eco‐friendly synthesis of gelatin‐capped bimetallic Au–Ag nanoparticles for chemiluminescence detection of anticancer raloxifene hydrochloride

This study described the utility of green analytical chemistry in the synthesis of gelatin‐capped silver, gold and bimetallic gold–silver nanoparticles (NPs). The preparation of nanoparticles was based on the reaction of silver nitrate or chlorauric acid with a 1.0 wt% aqueous gelatin solution at 50°C. The gelatin‐capped silver, gold and bimetallic NPs were characterized using transmission electron microscopy, UV–vis, X‐ray diffraction and Fourier transform infrared spectroscopy, and were used to enhance a sensitive sequential injection chemiluminescence luminol–potassium ferricyanide system for determination of the anticancer drug raloxifene hydrochloride. The developed method is eco‐friendly and sensitive for chemiluminescence detection of the selected drug in its bulk powder, pharmaceutical injections and biosamples. After optimizing the conditions, a linear relationship in the range of 1.0 × 10^–9 to 1.0 × 10^–1 mol/L was obtained with a limit of detection of 5.0 × 10^–10 mol/L and a limit of quantification of 1.0 × 10^‐9 mol/L. Statistical treatment and method validation were performed based on ICH guidelines. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of the Electrostatic Repulsion Between Nanoparticles on Colorimetric Sensing: An Investigation of Determination of Hg2+ with Silver Nanoparticles

The electrostatic repulsion between metal nanoparticles has an important effect on the colorimetric assays based on the aggregation of nanoparticles. In this work, an Hg²⁺ colorimetric sensor based on silver nanoparticles (AgNPs) was used as a model system to study the effects of electrostatic repulsion. Adenine nucleotides carrying different numbers of phosphate groups, adenosine monophosphate (AMP), adenosine diphosphate, and adenosine triphosphate, were used to functionalize AgNPs, respectively. Three kinds of AgNPs displayed different responses to Hg²⁺ ions due to the difference in electrostatic repulsion force, which is resulted from the varying of the number of phosphate groups. The density of negative charges on the surface of AgNPs exhibited a great affect on the size of the AgNPs, detection sensitivity and response range for Hg²⁺ ions. On these bases, the AMP-modified AgNPs were developed into highly sensitive colorimetric sensor to determine Hg²⁺ ions in aqueous solution, which showed a high sensitivity of 0.5 nM and excellent selectivity for Hg²⁺. The Hg²⁺ levels in water samples were determined using AMP-AgNPs with satisfied recovery. The studies on the role of electrostatic repulsion in the colorimetric assays will facilitate the development of more sensitive colorimetric sensors.     

Ultrasensitive and selective detection of copper (II) and mercury (II) ions by dye-coded silver nanoparticle-based SERS probes

A simple and distinctive method for the ultrasensitive detection of Cu(2+) and Hg(2+) based on surface-enhanced Raman scattering (SERS) using cysteine-functionalized silver nanoparticles (AgNPs) attached with Raman-labeling molecules was developed. The glycine residue in a silver nanoparticle-bound cysteine can selectively bind with Cu(2+) and Hg(2+) and form a stable inner complex. Silver nanoparticles co-functionalized with cysteine and 3,5-Dimethoxy-4-(6'-azobenzotriazolyl)phenol (AgNP conjugates) can be used to detect Cu(2+) and Hg(2+) based on aggregation-induced SERS of the Raman tags. The addition of SCN(-) to the analyte can successfully mask Hg(2+) and allow for the selective detection of Cu(2+). This SERS-based assay showed an unprecedented limit of detection (LOD) of 10pM for Cu(2+) and 1pM for Hg(2+); these LODs are a few orders of magnitude more sensitive than the typical colorimetric approach based on the aggregation of noble nanoparticles. The analysis of real water samples diluted with pure water was performed and verified this conclusion. We envisage that this SERS-based assay may provide a general and simple approach for the detection of other metal ions of interest, which can be adopted from their corresponding colorimetric assays that have already been developed with significantly improved sensitivity and thus have wide-range applications in many areas.     

Rapid biological synthesis of silver nanoparticles using plant leaf extracts

Five plant leaf extracts (Pine, Persimmon, Ginkgo, Magnolia and Platanus) were used and compared for their extracellular synthesis of metallic silver nanoparticles. Stable silver nanoparticles were formed by treating aqueous solution of AgNO₃ with the plant leaf extracts as reducing agent of Ag⁺ to Ag⁰. UV-visible spectroscopy was used to monitor the quantitative formation of silver nanoparticles. Magnolia leaf broth was the best reducing agent in terms of synthesis rate and conversion to silver nanoparticles. Only 11 min was required for more than 90% conversion at the reaction temperature of 95 °C using Magnolia leaf broth. The synthesized silver nanoparticles were characterized with inductively coupled plasma spectrometry (ICP), energy dispersive X-ray spectroscopy (EDS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and particle analyzer. The average particle size ranged from 15 to 500 nm. The particle size could be controlled by changing the reaction temperature, leaf broth concentration and AgNO₃ concentration. This environmentally friendly method of biological silver nanoparticles production provides rates of synthesis faster or comparable to those of chemical methods and can potentially be used in various human contacting areas such as cosmetics, foods and medical applications.