Metal-based nanoparticles have been extensively investigated for a set of biomedical applications. According to the World Health Organization, in addition to their reduced size and selectivity for bacteria, metal-based nanoparticles have also proved to be effective against pathogens listed as a priority. Metal-based nanoparticles are known to have non-specific bacterial toxicity mechanisms (they do not bind to a specific receptor in the bacterial cell) which not only makes the development of resistance by bacteria difficult, but also broadens the spectrum of antibacterial activity. As a result, a large majority of metal-based nanoparticles efficacy studies performed so far have shown promising results in both Gram-positive and Gram-negative bacteria. The aim of this review has been a comprehensive discussion of the state of the art on the use of the most relevant types of metal nanoparticles employed as antimicrobial agents. A special emphasis to silver nanoparticles is given, while others (e.g., gold, zinc oxide, copper, and copper oxide nanoparticles) commonly used in antibiotherapy are also reviewed. The novelty of this review relies on the comparative discussion of the different types of metal nanoparticles, their production methods, physicochemical characterization, and pharmacokinetics together with the toxicological risk encountered with the use of different types of nanoparticles as antimicrobial agents. Their added-value in the development of alternative, more effective antibiotics against multi-resistant Gram-negative bacteria has been highlighted.

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Metal-based nanoparticles as antimicrobial agents: an overview.

Much work has been carried out in recent years on the beneficial effect of phenolic compounds which act as natural antioxidants and help to neutralize free radicals. We analysed the antioxidant activity of the rutin (quercetin-3-rhamnosyl glucoside) using different assays including: total antioxidant activity and reducing power, hydroxyl radical scavenging assay, superoxide radical scavenging assay, 1,1-diphenyl-2-picryl-hydrazyl (DPPH) radical scavenging assay and lipid peroxidation assay which uses egg yolk as the lipid-rich source. Total antioxidant capacity was determined by the assay based on the decrease in absorbance of β-carotene by the sample. Rutin exhibited strong DPPH radical scavenging activity. At the concentration of 0.05 mg/ml, ascorbic acid (Vc), butylated hydroxytoluene (BHT) and rutin showed 92.8%, 58.8%, and 90.4% inhibition, respectively. In addition, rutin had effective inhibition of lipid peroxidation. Those various antioxidant activities were compared to standard antioxidants such as BHT and Vc.

In vitro antioxidant properties of rutin

Silver Nanoparticles: Therapeutical Uses, Toxicity, and Safety Issues

Chitin is the structural material of crustaceans, insects, and fungi, and is the second most abundant biopolymer after cellulose on earth. Chitosan, a deacetylated derivative of chitin, can be obtained by deacetylation of chitin. It is a functionally versatile biopolymer due to the presence of amino groups responsible for the various properties of the polymer. Although it has been used for various industrial applications, the recent one is its use as a biodegradable antimicrobial food packaging material. Much research has been focused on chitosan-based flexible food packaging and edible food coatings to compete with conventional non-biodegradable plastic-based food packaging materials. Various strategies have been used to improve the properties of chitosan - using plasticizers and cross-linkers, embedding the polymer with fillers such as nanoparticles, fibers, and whiskers, and blending the polymer with natural extracts and essential oils and also with other natural and synthetic polymers. However, much research is still needed to bring this biopolymer to industrial levels for the food packaging applications. Industrial relevance As a major by-product of the seafood industry, a massive amount of crustacean shell waste is generated each year, which can be used to produce value-added chitin, which can be converted to chitosan using a relatively simple deacetylation process. Being extracted from a bio-waste product using many energy-efficient methods, chitosan is much cheaper as compared to other biopolymers. Nevertheless, the exceptional properties of chitosan make it a relatively stronger candidate for food packaging applications. Chitosan has already been used in various industries, such as biomedical, agriculture, water treatment, cosmetics, textile, photography, chromatography, electronics, paper industry, and food industry. This review article compiles all the essential literature up to the latest developments of chitosan as a potential food packaging material and the outcomes of its practical utilization for this purpose.

Chitosan-based biodegradable functional films for food packaging applications

An efficient biosynthesis process for the rapid production of nanoparticles would enable the development of a “microbial nanotechnology” for mass-scale production. In the present research, biological silver nanoparticle was synthesized extracellularly by using the fungus, Trichoderma longibrachiatum, where the cell filtrate of the fungus was used as a reducing and stabilizing agent in the process of nanoparticle synthesis. Different physical parameters such as fungal biomass concentration (1, 5, 10, 15, and 20 g), temperature (25, 28, and 33 °C), incubation time (0–120 h), and agitation (shaken or not shaken) were investigated, in order to determine the optimal conditions for nanoparticle biosynthesis. The stability and antifungal properties of the synthesized silver nanoparticles (AgNPs) were also determined. Data revealed that a combination of 10 g fungal biomass, a reaction temperature of 28 °C, a 72-h incubation time, and without shaking were the optimum conditions for the synthesis of the silver nanoparticles. Visual observation of brown color is an indication of silver nanoparticle production. UV–vis spectroscopy showed maximum absorption at 385 nm with the optimum conditions. Transmission electron microscopy (TEM) revealed the formation of monodispersed spherical shape with a mean diameter of 10 nm. Fourier transformation infrared (FTIR) showed bands at1634.92 and 3269.31 cm−1. Dynamic light scattering (DLS) supported that the Z-average size was 24.43 and 0.420 PdI value. Zeta potential showed − 19.7 mV with a single peak. The AgNPs synthesized through this biosystem approach were relatively stable up to 2 months after synthesis. The use of AgNPs as antifungal led to significant reductions in the number of forming colonies for many plant pathogenic fungi, with efficiencies reaching up to 90% against Fusarium verticillioides, Fusarium moniliforme, Penicillium brevicompactum, Helminthosporium oryzae, and Pyricularia grisea. However, further research should be carried out in order to determine the toxic effect of AgNPs before mass production and use of agricultural applications.

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Biosynthesis and characterization of silver nanoparticles using Trichoderma longibrachiatum and their effect on phytopathogenic fungi

Silver loaded aminosilane modified halloysite for the preparation of carrageenan-based functional films

The biosynthesis of silver nanoparticles (AgNPs) has been carried out by using the extracellular filtrate of the fungal strain, @@ Aspergillus foetidus . The synthesized nano particles have been characterized following different biophysical techniques. The results obtained from the studies of antifungal activities of AgNPs were found to be of utmost significance. Growth of @@ A. foetidus both in liquid and solid CD media have been monitored in presence of the nanoparticles (0–40 ppm). Medium free dry biomass of the fungi was collected and emphasis has been laid on the assay of catalase activity, lipid per oxidation, thiol and protein content estimation and leakage of thiol, protein content. Growth of fungi in the presence of AgNPs was significantly inhibited in a dose dependent manner. Adherence of AgNPs on the fungal strain was realized by field emission scanning electron microscopy, and energy-dispersive X-ray spectroscopy, which indicated presence of silver nanomaterials in the surface of fungal mycelium. The growth of the fungus was found to be remarkably decreased with the increase in concentration of AgNPs and a considerable change in the activities and contents of all of the biochemical parameters considered indicated a plausible mechanistic mode of action of biosynthesized AgNPs establishing its antifungal activity.

Effect of biosynthesized silver nanoparticles on the growth and some biochemical parameters of @@ Aspergillus foetidus

Biosynthesis of Silver Nanoparticles by Aspergillus foetidus : Optimization of Physicochemical Parameters

Investigation of Interaction Between Casein Enzyme Hydrolysate and Biosynthesized Silver Nanoparticles by Spectroscopy

Sulfur nanoparticles (SNPs) have recently caught the scientific community's attention due to their improved physicochemical attributes compared to the bulk counterparts. However, the SNPs' high hydrophobicity and instability in aqueous solutions have limited their actual application potential. Here, kiwifruit peel polyphenols were used as natural capping agents obtained from agro-waste to cap SNPs. The capped particles were ~ 90 nm in size, smaller than ~ 130 nm for uncapped particles. After capping, the zeta potential value was − 45 mV, which is way better than − 28 mV for uncapped particles indicating better dispersion and stability in the aqueous suspension. The XPS spectra of SNPs confirmed successful capping by organic kiwi peel polyphenols showing intense peaks for C1s and O1s levels. Besides, the SNPs' functionality was also enhanced as they displayed a two-fold increase in antibacterial activity.

Swarup Roy

Papers

Silver loaded aminosilane modified halloysite for the preparation of carrageenan-based functional films

Effect of biosynthesized silver nanoparticles on the growth and some biochemical parameters of @@ Aspergillus foetidus

Biosynthesis of Silver Nanoparticles by Aspergillus foetidus : Optimization of Physicochemical Parameters

Investigation of Interaction Between Casein Enzyme Hydrolysate and Biosynthesized Silver Nanoparticles by Spectroscopy

Enhanced functionality of green synthesized sulfur nanoparticles using kiwifruit (Actinidia deliciosa) peel polyphenols as capping agents