Antimicrobial activity of highly stable silver nanoparticles embedded in agar–agar matrix as a thin film

Antifungal Activity of Nanobiocomposite Films Based on Silver Nanoparticles Obtained Through Green Synthesis

The high incidence of Candida albicans infections has raised concerns regarding side effects and drug resistance, compounded by a limited number of alternative drugs. Silver nanoparticles (AgNPs) have prominent antimicrobial activity, but effective administration remains a challenge. In this study, AgNPs were synthesized via a green chemistry approach, using glucose as a reducing agent, and incorporated into an agar matrix to form a film (AgFilm). The AgNPs and AgFilm were characterized by Ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and atomic force microscopic (AFM). The UV-Vis spectra of the AgNPs and AgFilm showed bands at 415 and 413 nm, respectively. The PXRD and UV-Vis data suggest that the growth of AgNPs was effectively inhibited in the AgFilm. The diameter of AgNPs dispersed in AgFilm was 76 ± 42 nm, and the thickness of the film and 35 ± 3 µm. The antifungal activity of AgFilm was evaluated against 20 strains of C. albicans, demonstrating high antifungal activity with an inhibition zone of 19 ± 2 mm. Therefore, AgFilm could be a promising option for the treatment of superficial C. albicans infections.

Biogenic Synthesis of Copper Nanoparticles: A Systematic Review of Their Features and Main Applications

Nanotechnology is an innovative field of study that has made significant progress due to its potential versatility and wide range of applications, precisely because of the development of metal nanoparticles such as copper. Nanoparticles are bodies composed of a nanometric cluster of atoms (1-100 nm). Biogenic alternatives have replaced their chemical synthesis due to their environmental friendliness, dependability, sustainability, and low energy demand. This ecofriendly option has medical, pharmaceutical, food, and agricultural applications. When compared to their chemical counterparts, using biological agents, such as micro-organisms and plant extracts, as reducing and stabilizing agents has shown viability and acceptance. Therefore, it is a feasible alternative for rapid synthesis and scaling-up processes. Several research articles on the biogenic synthesis of copper nanoparticles have been published over the past decade. Still, none provided an organized, comprehensive overview of their properties and potential applications. Thus, this systematic review aims to assess research articles published over the past decade regarding the antioxidant, antitumor, antimicrobial, dye removal, and catalytic activities of biogenically synthesized copper nanoparticles using the scientific methodology of big data analytics. Plant extract and micro-organisms (bacteria and fungi) are addressed as biological agents. We intend to assist the scientific community in comprehending and locating helpful information for future research or application development.

Cellulose nanofibrils and silver nanoparticles enhances the mechanical and antimicrobial properties of polyvinyl alcohol nanocomposite film

Recent findings of microplastics in marine food such as fish, crabs and shrimps necessitate the need to develop biodegradable packaging materials. This study reports on the development of a biodegradable packing material from cellulose nanofibril-polyvinyl alcohol nanocomposite embedded with silver nanoparticles. Microcrystalline cellulose was isolated from sugarcane bagasse via the kraft process followed by conversion of cellulose I to cellulose II using NaOH/urea/water solution. The nanofibrils were then isolated using (2,2,6,6-Tetramethylpiperidin-1-yl) oxyl (TEMPO) and used as a reinforcing element in polyvinyl alcohol composite prepared through solvent casting. The tensile strength, water solubility, optical properties, water vapor permeability and wettability of the prepared films were then evaluated. The antimicrobial potency of the films was evaluated using the disc diffusion antimicrobial assay against selected microorganisms.

Assessment of Binary Agarose-Carbopol Buccal Gels for Mucoadhesive Drug Delivery: Ex Vivo and In Vivo Characterization

Agarose (AG) is a naturally occurring biocompatible marine seaweed extract that is converted to hydrocolloid gel in hot water with notable gel strength. Currently, its mucoadhesion properties have not been fully explored. Therefore, the main aim of this study was to evaluate the mucoadhesive potential of AG binary dispersions in combination with Carbopol 934P (CP) as mucoadhesive gel preparations. The gels fabricated via homogenization were evaluated for ex vivo mucoadhesion, swelling index (SI), dissolution and stability studies. The mucoadhesive properties of AG were concentration dependent and it was improved by the addition of CP. Maximum mucoadhesive strength (MS) (27.03 g), mucoadhesive flow time (FT) (192.2 min), mucoadhesive time in volunteers (MT) (203.2 min) and SI (23.6% at 4 h) were observed with formulation F9. The mucoadhesive time investigated in volunteers (MT) was influenced by AG concentration and was greater than corresponding FT values. Formulations containing 0.3%, w/v AG (F3 and F9) were able to sustain the release (~99%) for both drugs till 3 h. The optimized formulation (F9) did not evoke any inflammation, irritation or pain in the buccal cavity of healthy volunteers and was also stable up to 6 months. Therefore, AG could be considered a natural and potential polymer with profound mucoadhesive properties to deliver drugs through the mucosal route.

Agar-based edible films for food packaging applications - A review

Agar is a biopolymer extracted from certain red algae. The continuous and transparent film made from agar gum is becoming a common and renewable alternative for plastic-based food packaging materials. However, plain agar film suffers from brittleness, high moisture permeability, and poor thermal stability. Considerable researches have been devoted to improving the properties of agar films to extend their applications. These include reinforcements by nanomaterials, blending with other biopolymers, and incorporating plasticizers, hydrophobic components, or antimicrobial agents into their structure. This article comprehensively reviews the functional properties and defects of edible films made from agar gum. Also, it describes various strategies and components used to make an agar film with desirable properties. Moreover, the applications of agar-based edible films with improved functionality for food packaging are discussed.

Fumaric acid incorporated Ag/agar-agar hybrid hydrogel: A multifunctional avenue to tackle wound healing

Wound and its treatment is one of the major health concerns throughout the globe. Various extrinsic and intrinsic factors can influence the dynamics of healing mechanism. One such extrinsic factor is moist environment in wound healing. The advantages of optimum hydration in wound healing are enhanced autolytic debridement, angiogenesis and accelerated cell proliferation and collagen formation. But hydrated wounds often end up with patient's uncomfortability, associated infection, and tissue lipid peroxidation. Healing process prefers antimicrobial, anti-inflammatory and optimum moist microenvironment. Here, we have synthesized fumaric acid incorporated agar-silver hydrogel (AA-Ag-FA); characterized by UV-Visible spectroscopy, FTIR spectroscopy and TEM. The surface morphology is evaluated through SEM. The size of the silver nanoparticles (Ag NPs) was found to be 10-15 nm. The hydrogel shows potential antibacterial effect against Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa which are predominantly responsible for wound infection. The gel shows reasonable antioxidant property evaluated through 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Topical application of the gel on the wound site heals the wound at much faster rate even compared to standard (Mega heal, Composition: Colloidal silver 32 ppm hydrogel) gel. Histological analysis reveals better tissue proliferation (i.e. epithelialization), more granulation tissue formation, neovascularisation, fibroblast and mature collagen bundles. The lipid peroxidation of wound tissue estimated through malondialdehyde (MDA) assay was found to be reasonably less when treated with AA-Ag-FA hydrogel compared to standard (Mega heal). Cytotoxicity of the samples tested through MTT assay and live-dead cell staining shows its nontoxic biocompatibility nature. In our hydrogel scaffold, the bio-degradable agar-agar provides the moist environment; the Ag NPs inside the gel acts as bactericidal agent and fumaric acid facilities the antioxidant and angiogenesis path implicitly.

Biological mediated Ag nanoparticles from Barleria longiflora for antimicrobial activity and photocatalytic degradation using methylene blue

The present study focuses on extraction of green synthesized silver nanoparticles (Ag-NPs) from Barleria longiflora L. leaves for antibacterial and photocatalytic activities. The extracted Ag-NPs have been characterized by XRD, FTIR, FE-SEM with EDX, HR-TEM accompanied SAED pattern and UV-Visible absorption spectroscopic techniques. Spectral studies confirmed the UV-Visible absorption spectrum of the Ag-NPs at a wavelength of 443 nm and a good crystalline nature with a face-centered cubic crystal structure using XRD spectrum. Surface topography and the presence of Ag in the prepared sample have been confirmed from SEM and EDX measurements. Various functional groups present in the sample have been examined using FT-IR spectroscopic analysis. A homogeneous dispersion of spherical form nanoparticles with a usual size of 2.4 nm was confirmed by visualization using FE-SEM and HR-TEM. Moreover, Ag-NPs stimulate a strong inhibition of Enterococcus sp., Streptococcus sp, Bacillus megaterium, Pseudomonas putida, Pseudomonas aeruginosa and Staphylocouus aureus; with a good catalytic reduction activity for degrading organic methylene blue (MB) dye. Therefore, silver nanoparticles obtained from Barleria longiflora L. have potential application in medicine and photocatalytic dye degradation processes.

Antibacterial Interactions of Colloid Nanosilver with Eugenol and Food Ingredients

This study was conducted to investigate antibacterial properties of the colloidal silver nanoparticles (SNPs) and eugenol, alone and in combination, on Staphylococcus aureus and Salmonella Typhimurium and their interactions with food constituents (fat, protein, and carbohydrate). We examined antibacterial activities of SNPs and eugenol in Luria-Bertani (LB) broth and 1.5 and 3% fat ultrahigh-temperature (UHT) milk. MICs of eugenol and SNPs (particle size of 31.3 nm) were also investigated in the presence of sunflower oil, meat extract, and starch at concentrations of 2, 5, and 10% to examine the interactions between food constituents and antimicrobial agents. MICs and MBCs of eugenol and SNPs for both bacteria were at 2,500 and 25 μg/mL, respectively. Combinations of the two substances had additive and synergistic effects on Salmonella Typhimurium and S. aureus, respectively. Both compounds had bactericidal activity. In food matrices, results indicated that eugenol only in sunflower oil at 5 and 10% concentrations had significant antibacterial activity. A similar result was achieved for SNPs with 10% meat extract. In LB broth, eugenol at 2,500 and 5,000 μg/mL achieved 6-log reductions in the microbial population of both bacteria after 3 h, while SNPs achieved the same effect after 9 h. In UHT milk with 1.5% fat, eugenol at 5,000 μg/mL and SNPs at 25 μg/mL achieved 6-log reductions in bacterial populations after 24 h. Thus, the antimicrobial activity of both eugenol and SNPs depended on the medium in which the experiment was conducted, and the combination of both antimicrobial agents increased the antimicrobial effect.

Antibacterial ability of immobilized silver nanoparticles in agar-agar films co-doped with magnesium ions

The antibacterial ability of in situ prepared nanometer-sized silver particles, immobilized in agar-agar films, was studied as a function of the concentration of co-dopant, magnesium ions. Content of inorganic components in hybrid films was determined using inductively coupled plasma optic emission spectroscopy, and found to be low (<2 wt.-%). Morphology of prepared hybrid films, studied by transmission electron microscopy, revealed the presence of non-agglomerated and randomly distributed 10-20 nm silver nanoparticles (Ag NPs) within the agar-agar matrices. Fourier-transform infrared spectroscopy indicated the distinct chemical interaction between Ag NPs and polymer chains. Thermogravimetric analysis, as well as the determination of tensile strength, Young's modulus, and elongation at break showed improvement of thermal stability and mechanical properties of agar-agar matrices upon the incorporation of Ag NPs due to high compatibility between the hydrophilic organic component and inorganic components. The complete microbial reduction of Gram-positive bacteria Staphylococcus aureuswas observed for all agar-silver films, while satisfactory results were observed for Gram-negative bacteria Pseudomonas aeruginosa (≥99.6%). The release of Ag⁺ ions is suppressed by the increase of the concentration of Mg²⁺ ions and it was found to be significantly smaller (≤0.24 ppm) than the harmful ecological level (1 ppm).

Rapid antibacterial effect of sunlight-exposed silicon nanowire arrays modified with Au/Ag alloy nanoparticles

Au/Ag alloy nanoparticles modified silicon nanowire arrays can kill bacterial cells in several minutes under sunlight due to their photothermal and photocatalytic activities.

Silver Nanoparticles Stabilised by Cationic Gemini Surfactants with Variable Spacer Length

The present study is focused on the synthesis and investigation of the physicochemical and biological properties of silver nanoparticles stabilized with a series of cationic gemini surfactants having a polymethylene spacer of variable length. UV-VIS spectroscopy, dynamic light scattering, scanning electron microscopy and zeta potential measurements were applied to provide physicochemical characterization of the silver nanoparticles. The mean size values of the nanoparticles were found to be in the 50 to 115 nm range. From the nanoparticle size distributions and scanning electron microscopy images it results that a population of small nanoparticles with the size of several nanometers was confirmed if the nanoparticles were stabilized with gemini molecules with either a short methylene spacer (two or four −CH₂− groups) or a long spacer (12 −CH₂− groups). The average zeta potential value for silver nanoparticles stabilized with gemini molecules is roughly independent of gemini surfactant spacer length and is approx. +58 mV. An interaction model between silver nanoparticles and gemini molecules which reflects the gained experimental data, is suggested. Microbicidal activity determinations revealed that the silver nanoparticles stabilized with gemini surfactants are more efficient against Gram-negative bacteria and yeasts, which has a direct relation to the interaction mechanism of nanoparticles with the bacterial cell membrane and its structural composition.

Toxicity of silver nanoparticles in biological systems: Does the complexity of biological systems matter?

Currently, nanomaterials are more frequently in our daily life, specifically in biomedicine, electronics, food, textiles and catalysis just to name a few. Although nanomaterials provide many benefits, recently their toxicity profiles have begun to be explored. In this work, the toxic effects of silver nanoparticles (35nm-average diameter and Polyvinyl-Pyrrolidone-coated) on biological systems of different levels of complexity was assessed in a comprehensive and comparatively way, through a variety of viability and toxicological assays. The studied organisms included viruses, bacteria, microalgae, fungi, animal and human cells (including cancer cell lines). It was found that biological systems of different taxonomical groups are inhibited at concentrations of silver nanoparticles within the same order of magnitude. Thus, the toxicity of nanomaterials on biological/living systems, constrained by their complexity, e.g. taxonomic groups, resulted contrary to the expected. The fact that cells and virus are inhibited with a concentration of silver nanoparticles within the same order of magnitude could be explained considering that silver nanoparticles affects very primitive cellular mechanisms by interacting with fundamental structures for cells and virus alike.

Visual and optical detection of hypochlorite in water samples based on etching of gold/silver alloy nanoparticles

In this work, we have described the cost-effective, simple, selective and sensitive approach for the detection of hypochlorite (ClO⁻) using gold/silver alloy nanoparticles (Au/Ag alloy NPs) as a colorimetric probe.

Gelatin-based dissolvable antibacterial films reinforced with metallic nanoparticles

Six different types of nanoparticles (Au, Ag, Cu, AuAg, AuCu, and AgCu) were prepared using an aqueous extract of Artemisia scoparia and gelatin/nanoparticle composite films were prepared.

Biobased silver nanocolloid coating on silk fibers for prevention of post-surgical wound infections

Bombyx mori silk fibers are an important biomaterial and are used in surgical sutures due to their remarkable biocompatibility. The major drawback to the application of biomaterials is the risk of bacterial invasion, leading to clinical complications. We have developed an easy and cost-effective method for fabrication of antibacterial silk fibers loaded with silver nanoparticles (AgNPs) by an in situ and ex situ process using an aqueous extract of Rhizophora apiculata leaf. Scanning electron microscopy revealed that well dispersed nanoparticles impregnated the silk fibers both in situ and ex situ. The crystalline nature of the AgNPs in the silk fibers was demonstrated by X-ray diffraction. The thermal and mechanical properties of the silk fibers were enhanced after they were impregnated with AgNPs. The silver-coated silk fibers fabricated by the in situ and ex situ method exhibited more than 90% inhibition against Pseudomonas aeruginosa and Staphylococcus aureus. Silk fibers doped with AgNPs were found to be biocompatible with 3T3 fibroblasts. The results obtained represent an important advance towards the clinical application of biocompatible AgNP-loaded silk fibers for prevention of surgical wound infections.

Silver nanoparticle-doped zirconia capillaries for enhanced bacterial filtration

Membrane clogging and biofilm formation are the most serious problems during water filtration. Silver nanoparticle (Ag_nano) coatings on filtration membranes can prevent bacterial adhesion and the initiation of biofilm formation. In this study, Ag_nano are immobilized via direct reduction on porous zirconia capillary membranes to generate a nanocomposite material combining the advantages of ceramics being chemically, thermally and mechanically stable with nanosilver, an efficient broadband bactericide for water decontamination. The filtration of bacterial suspensions of the fecal contaminant Escherichia coli reveals highly efficient bacterial retention capacities of the capillaries of 8 log reduction values, fulfilling the requirements on safe drinking water according to the U.S. Environmental Protection Agency. Maximum bacterial loading capacities of the capillary membranes are determined to be 3 × 10⁹ bacterial cells/750 mm² capillary surface until back flushing is recommendable. The immobilized Ag_nano remain accessible and exhibit strong bactericidal properties by killing retained bacteria up to maximum bacterial loads of 6 × 10⁸ bacterial cells/750 mm² capillary surface and the regenerated membranes regain filtration efficiencies of 95–100%. Silver release is moderate as only 0.8% of the initial silver loading is leached during a three-day filtration experiment leading to average silver contaminant levels of 100 μg/L.

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Silver nanoparticle-doped zirconia capillary membrane for water filtration purposes

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Characterization of the silver loading capacity of the capillary membrane

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Excellent bacteria filtration performances of log reduction values of 8

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Efficient killing of 6 × 10⁸  filtrated bacteria/750 mm² capillary surface

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Back flushing enables the regeneration of the membrane by removing dead bacteria.

Ultrastructural analysis of Candida albicans when exposed to silver nanoparticles

Candida albicans is the most common fungal pathogen in humans, and recently some studies have reported the antifungal activity of silver nanoparticles (AgNPs) against some Candida species. However, ultrastructural analyses on the interaction of AgNPs with these microorganisms have not been reported. In this work we evaluated the effect of AgNPs on C. albicans, and the minimum inhibitory concentration (MIC) was found to have a fungicidal effect. The IC₅₀ was also determined, and the use of AgNPs with fluconazole (FLC), a fungistatic drug, reduced cell proliferation. In order to understand how AgNPs interact with living cells, the ultrastructural distribution of AgNPs in this fungus was determined. Transmission electron microscopy (TEM) analysis revealed a high accumulation of AgNPs outside the cells but also smaller nanoparticles (NPs) localized throughout the cytoplasm. Energy dispersive spectroscopy (EDS) analysis confirmed the presence of intracellular silver. From our results it is assumed that AgNPs used in this study do not penetrate the cell, but instead release silver ions that infiltrate into the cell leading to the formation of NPs through reduction by organic compounds present in the cell wall and cytoplasm.

Incorporation of essential oils and nanoparticles in pullulan films to control foodborne pathogens on meat and poultry products

The incorporation of essential oils and nanotechnology into edible films has the potential to improve the microbiological safety of foods. The aim of this study was to evaluate the effectiveness of pullulan films containing essential oils and nanoparticles against 4 foodborne pathogens. Initial experiments using plate overlay assays demonstrated that 2% oregano essential oil was active against Staphylococcus aureus and Salmonella Typhimurium, whereas Listeria monocytogenes and Escherichia coli O157:H7 were not inhibited. Two percent rosemary essential oil was active against S. aureus, L. monocytogenes, E. coli O157:H7, and S. Typhimurium, when compared with 1%. Zinc oxide nanoparticles at 110 nm were active against S. aureus, L. monocytogenes, E. coli O157:H7, and S. Typhimurium, when compared with 100 or 130 nm. Conversely, 100 nm silver (Ag) nanoparticles were more active against S. aureus than L. monocytogenes. Using the results from these experiments, the compounds exhibiting the greatest activity were incorporated into pullulan films and found to inhibit all or some of the 4 pathogens in plate overlay assays. In challenge studies, pullulan films containing the compounds effectively inhibited the pathogens associated with vacuum packaged meat and poultry products stored at 4 °C for up to 3 wk, as compared to control films. Additionally, the structure and cross-section of the films were evaluated using electron microscopy. The results from this study demonstrate that edible films made from pullulan and incorporated with essential oils or nanoparticles may improve the safety of refrigerated, fresh or further processed meat and poultry products.

The antimicrobial effect of silicon nanowires decorated with silver and copper nanoparticles

The paper reports on the preparation and antibacterial activity of silicon nanowire (SiNW) substrates coated with Ag or Cu nanoparticles (NPs) against Escherichia coli (E. coli) bacteria. The substrates are easily prepared using the metal-assisted chemical etching of crystalline silicon in hydrofluoric acid/silver nitrate (HF/AgNO3) aqueous solution. Decoration of the SiNWs with metal NPs is achieved by simple immersion in HF aqueous solutions containing silver or copper salts. The SiNWs coated with Ag NPs are biocompatible with human lung adenocarcinoma epithelial cell line A549 while possessing strong antibacterial properties to E. coli. In contrast, the SiNWs decorated with Cu NPs showed higher cytotoxicity and slightly lower antibacterial activity. Moreover, it was also observed that leakage of sugars and proteins from the cell wall of E. coli in interaction with SiNWs decorated with Ag NPs is higher compared to SiNWs modified with Cu NPs.

1.5 V battery driven reduced graphene oxide-silver nanostructure coated carbon foam (rGO-Ag-CF) for the purification of drinking water

A porous carbon foam (CF) electrode modified with a reduced graphene oxide-Ag (rGO-Ag) nanocomposite has been fabricated to purify water. It can perform as an antibacterial device by killing pathogenic microbes with the aid of a 1.5 V battery, with very little power consumption. The device is recycled ten times with good performance for long term usage. It is shown that the device may be implemented as a fast water purifier to deactivate the pathogens in drinking water.

Nano-technology for targeted drug delivery to combat antibiotic resistance

Several microbes have evolved clinically significant resistance against almost every available antibiotic. Yet the development of new classes of antibiotics has lagged far behind our growing need. Frequent and suboptimal use of antibiotics particularly in developing countries aggravated the problem by increasing the rate of resistance. Therefore, developing new and multidimensional strategies to combat microbial infections is warranted. These include i) modification of existing antibiotics, ii) searching new and novel antibiotics, iii) development and improvement of antibiotics carrier system to reduce amount and frequency of antibiotic doses, iv) development of targeted antibiotic delivery systems. Here, the authors discuss trends and development of nano-materials and alternative antimicrobials to solve the problem of antibiotic resistance.

Ag@AgI, core@shell structure in agarose matrix as hybrid: synthesis, characterization, and antimicrobial activity

A novel in situ core@shell structure consisting of nanoparticles of Ag (Ag Nps) and AgI in agarose matrix (Ag@AgI/agarose) has been synthesized as a hybrid, in order to have an efficient antibacterial agent for repetitive usage with no toxicity. The synthesized core@shell structure is very well characterized by XRD, UV-visible, photoluminescence, and TEM. A detailed antibacterial studies including repetitive cycles are carried out on Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus aureus (S. aureus) bacteria in saline water, both in dark and on exposure to visible light. The hybrid could be recycled for the antibacterial activity and is nontoxic toward human cervical cancer cells (HeLa cells). The water insoluble Ag@AgI in agarose matrix forms a good coating on quartz, having good mechanical strength. EPR and TEM studies are carried out on the Ag@AgI/agarose and the bacteria, respectively, to elucidate a possible mechanism for killing of the bacteria.

Development of surface plasmon resonance-based sensor for detection of silver nanoparticles in food and the environment

Silver nanoparticles are recognized as effective antimicrobial agents and have been implemented in various consumer products including washing machines, refrigerators, clothing, medical devices, and food packaging. Alongside the silver nanoparticles benefits, their novel properties have raised concerns about possible adverse effects on biological systems. To protect consumer's health and the environment, efficient monitoring of silver nanoparticles needs to be established. Here, we present the development of human metallothionein (MT) based surface plasmon resonance (SPR) sensor for rapid detection of nanosilver. Incorporation of human metallothionein 1A to the sensor surface enables screening for potentially biologically active silver nanoparticles at parts per billion sensitivity. Other protein ligands were also tested for binding capacity of the nanosilver and were found to be inferior to the metallothionein. The biosensor has been characterized in terms of selectivity and sensitivity towards different types of silver nanoparticles and applied in measurements of real-life samples-such as fresh vegetables and river water. Our findings suggest that human MT1-based SPR sensor has the potential to be utilized as a routine screening method for silver nanoparticles, that can provide rapid and automated analysis dedicated to environmental and food safety monitoring.

Silver nanotoxicity using a light-emitting biosensor Pseudomonas putida isolated from a wastewater treatment plant

The effect of silver ions, nano- and micro-particles on a luminescent biosensor bacterium Pseudomonas putida originally isolated from activated sludge was assessed. The bacterium carrying a stable chromosomal copy of the lux operon (luxCDABE) was able to detect toxicity of ionic and particulate silver over short term incubations ranging from 30 to 240 min. The IC(50) values obtained at different time intervals showed that highest toxicity (lowest IC(50)) was obtained after 90 min incubation for all toxicants and this is considered the optimum incubation for testing. The data show that ionic silver is the most toxic followed by nanosilver particles with microsilver particles being least toxic. Release of nanomaterials is likely to have an effect on the activated sludge process as indicated by the study using a common sludge bacterium involved in biodegradation of organic wastes.

Migration of silver from nanosilver-polyethylene composite packaging into food simulants

An analytical method for the determination of silver in food simulants (3% (w/v) aqueous acetic acid or 95% (v/v) aqueous ethanol) was developed based on inductively coupled plasma mass spectrometry (ICP-MS). Recoveries ranged from 87% to 109% and RSDs ranged from 0.7% to 7.8%. The procedure was applied to determine the migration of silver from nanosilver-polyethylene food packaging film into food simulants at different temperatures and migration times. Results indicated that the maximum migration ratios were 1.70%, 3.00% and 5.60% for 3% (w/v) aqueous acetic acid at 20, 40 and 70 °C, respectively, while for 95% (v/v) aqueous ethanol the maximum migration ratios were 0.24%, 0.23% and 0.22% at 20, 40 and 70 °C.