Nanosilver, due to its small particle size and enormous specific surface area, facilitates more rapid dissolution of ions than the equivalent bulk material; potentially leading to increased toxicity of nanosilver. This, coupled with their capacity to adsorb biomolecules and interact with biological receptors can mean that nanoparticles can reach sub-cellular locations leading to potentially higher localized concentrations of ions once those particles start to dissolve or degrade in situ. Further complicating the story is the capacity for nanoparticles to generate reactive oxygen species, and to interact with, and potentially disturb the functioning of biomolecules such as proteins, enzymes and DNA. The fact that the nanoparticle size, shape, surface coating and a host of other factors contribute to these interactions, and that the particles themselves are evolving or ageing leads to further complications in terms of elucidating mechanisms of interaction and modes of action for silver nanoparticles, in contrast to dissolved silver species. This review aims to provide a critical assessment of the current understanding of silver nanoparticle toxicity, as well as to provide a set of pointers and guidelines for experimental design of future studies to assess the environmental and biological impacts of silver nanoparticles. In particular; in future we require a detailed description of the nanoparticles; their synthesis route and stabilisation mechanisms; their coating; and evolution and ageing under the exposure conditions of the assay. This would allow for comparison of data from different particles; different environmental or biological systems; and structure-activity or structure-property relationships to emerge as the basis for predictive toxicology. On the basis of currently available data; such comparisons or predictions are difficult; as the characterisation and time-resolved data is not available; and a full understanding of silver nanoparticle dissolution and ageing under different conditions is observed. Clear concerns are emerging regarding the overuse of nanosilver and the potential for bacterial resistance to develop. A significant conclusion includes the need for a risk-benefit analysis for all applications and eventually restrictions of the uses where a clear benefit cannot be demonstrated.

https://www.mdpi.com/1996-1944/6/6/2295/pdf

Mechanisms of Silver Nanoparticle Release, Transformation and Toxicity: A Critical Review of Current Knowledge and Recommendations for Future Studies and Applications.

Nanotechnology is the creation, manipulation and use of materials at the nanometre size scale (1 to 100 nm). At this size scale there are significant differences in many material properties that are normally not seen in the same materials at larger scales. Although nanoscale materials can be produced using a variety of traditional physical and chemical processes, it is now possible to biologically synthesize materials via environment-friendly green chemistry based techniques. In recent years, the convergence between nanotechnology and biology has created the new field of nanobiotechnology that incorporates the use of biological entities such as actinomycetes algae, bacteria, fungi, viruses, yeasts, and plants in a number of biochemical and biophysical processes. The biological synthesis via nanobiotechnology processes have a significant potential to boost nanoparticles production without the use of harsh, toxic, and expensive chemicals commonly used in conventional physical and chemical processes. The aim of this review is to provide an overview of recent trends in synthesizing nanoparticles via biological entities and their potential applications.

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Green Synthesis of Metallic Nanoparticles via Biological Entities

Green synthesis and characterization of silver nanoparticles using banana peel extract and their antimicrobial activity against representative microorganisms

Mosquitoes (Diptera: Culicidae) are a key threat for millions of people worldwide, since they act as vectors for devastating parasites and pathogens. Mosquito young instars are usually targeted with organophosphates, insect growth regulators and microbial control agents. Indoors residual spraying and insecticide-treated bed nets are also employed. However, these chemicals have strong negative effects on human health and the environment. Newer and safer tools have been recently implemented to enhance control of mosquitoes. In this review, I focus on characterization, effectiveness, and non-target effects of mosquitocidal nanoparticles synthesized using botanical products (mosquitocidal nanoparticles, MNP). The majority of plant-fabricated MNP are silver ones. The synthesis of MNP is usually confirmed by UV-visualization spectroscopy, followed by scanning electron microscopy or transmission electron microscopy, energy-dispersive X-ray spectroscopy, Fourier transform infrared spectroscopy, and X-ray diffraction studies. Interestingly, plant-synthesized metal nanoparticles have been reported as effective ovicides, larvicides, pupicides, adulticides, and oviposition deterrents against different mosquito species of medical and veterinary importance. Few parts per million of different MNP are highly toxic against the malaria vector Anopheles stephensi, the dengue vector Aedes aegypti, and the filariasis mosquito Culex quiquefasciatus. However, despite the growing number of evidences about the effectiveness of MNP, moderate efforts have been carried out to shed light on their possible non-target effects against mosquito's natural enemies and other aquatic organisms. In the final section, particular attention was dedicated to this issue. A number of hot areas that need further research and cooperation among parasitologists and entomologists are highlighted.

Plant-mediated biosynthesis of nanoparticles as an emerging tool against mosquitoes of medical and veterinary importance: a review

The synthesis of nanostructured materials, especially metallic nanoparticles, has accrued utmost interest over the past decade owing to their unique properties that make them applicable in different fields of science and technology. The limitation to the use of these nanoparticles is the paucity of an effective method of synthesis that will produce homogeneous size and shape nanoparticles as well as particles with limited or no toxicity to the human health and the environment. The biological method of nanoparticle synthesis is a relatively simple, cheap, and environmentally friendly method than the conventional chemical method of synthesis and thus gains an upper hand. The biomineralization of nanoparticles in protein cages is one of such biological approaches used in the generation of nanoparticles. This method of synthesis apart from being a safer method in the production of nanoparticles is also able to control particle morphology.

/pdf/biosynthesis-of-metal-nanoparticles-a-review-286kbpf5by.pdf

Biosynthesis of Metal Nanoparticles: A Review

The biological process with the ability to study the shape of particles produced would therefore be a limelight of modern nanotechnology. The bacterial strain Escherichia coli, used for the biosynthesis of silver nanoparticles were investigated. These silver nanoparticles were characterized by means of UV–vis spectroscopy, particle size analyzer. The nanoparticles exhibited maximum absorbance at 400 nm in UV–vis spectroscopy corresponding to the plasmon resonance of silver nanoparticles.

/pdf/microbial-production-of-silver-nanoparticles-4d7ljynbfm.pdf

Microbial Production of Silver Nanoparticles

Abstract Bioactive compounds refer to secondary metabolites extracted from plants, fungi, microbes, or animals. Besides having pharmacological or toxicological effects on organisms leading to utilization in food and pharmaceutical industries, the discovery of novel properties of such compounds has led to the diversification of their applications, ranging from cosmetics and functionalized biomaterials to bioremediation and alternate fuels. Conventional time-consuming and solvent-intensive methods of extraction are increasingly being replaced by green solvents such as ionic liquids, supercritical fluids, and deep eutectic solvents, as well as non-conventional methods of extraction assisted by microwaves, pulse electric fields, enzymes, ultrasound, or pressure. These methods, along with advances in characterization and optimization strategies, have boosted the commercial viability of extraction especially from agrowastes and organic residues, promoting a sustainable circular economy. Further development of microfluidics, optimization models, nanoencapsulation, and metabolic engineering are expected to overcome certain limitations that restrict the growth of this field, in the context of improving screening, extraction, and economy of processes, as well as retaining biodiversity and enhancing the stability and functionality of such compounds. This review is a compilation of the various extraction and characterization methods employed for bioactive compounds and covers major applications in food, pharmacy, chemicals, energy, and bioremediation. Major limitations and scope of improvement are also discussed. Graphical abstract 

/pdf/a-critical-look-at-challenges-and-future-scopes-of-bioactive-mdx7rvlc.pdf

A critical look at challenges and future scopes of bioactive compounds and their incorporations in the food, energy, and pharmaceutical sector

Abstract The production of bioproducts from microorganisms is a common practice in many industries for a long time now. In recent years, studies have proved that co-culturing microorganisms increase the yield of products by synergistically degrading the solid substrate in comparison with individual cultures. The review highlights the benefits of co-culturing microorganisms using solid state fermentation (SSF) to achieve higher productivity. Filamentous fungi of genus Trichoderma, Penicillium, and Aspergillus are extensively studied and used for co-culturing and mixed culturing under SSF. Co-cultured microorganisms are beneficial because of the synergistic expression of metabolic pathways of all the microorganisms. Co-culture enables combined metabolic activity at optimal process conditions for better utilization of substrates. Depending on the nature of the process and microorganism, bioreactors are designed and operated. This review mentions various purification methods that are used to improve the purity of the products obtained. The strengths and weaknesses of various bioreactors and their effect on the microorganisms used are explained in detail. This review also identifies the challenges of co-culturing microorganisms and analyses the diverse set of fields in which SSF finds its applications. Graphical Abstract 

/pdf/a-critical-look-at-bioproducts-co-cultured-under-solid-state-diwpew8y.pdf

A Critical Look at Bioproducts Co-cultured Under Solid State Fermentation and Their Challenges and Industrial Applications

Production of tannase from B. gottheilii M2S2 was studied under solid-state fermentation with an optimized medium consisting of polyurethane foam matrix of dimension 40 × 40 × 5 mm, impregnated with a liquid medium comprising (w/v): 4% tannic acid; 2% NH4NO3; 0.1% KH2PO4; 0.2% MgSO4; 0.1% NaCl and 0.05% CaCl2·2H2O in distilled water, having a pH of 4.7. Maximum tannase production of 56.87 U/L was obtained after 32 h of fermentation at 32 °C in static condition. This study deals with the evaluation of unstructured kinetic models to understand the behavior of biomass, tannase production and tannic acid degradation, with the fermentation time. The growth rate of B. gottheilii M2S2 was 0.0703 h−1 at 32 h of fermentation. Product (Y
 x/s) and biomass yield (Y
 p/s) coefficients were estimated as 1.77 U/g of tannic acid and 0.276 g of biomass/g of tannic acid. All the kinetic constants µ, α, β, m and n were evaluated using MATLAB 2015Rb program. The experimental and model-generated data showed a good correlation, which indicated that these models will describe tannase production and fermentation process.

Evaluation of model parameters for growth, tannic acid utilization and tannase production in Bacillus gottheilii M2S2 using polyurethane foam blocks as support

In recent years, the greener route of the deacetylation of chitin to chitosan using the enzyme chitin deacetylase has gained importance. Enzymatically converted chitosan with emulating characteristics has a broad range of applications, particularly in the biomedical field. Several recombinant chitin deacetylases from various environmental sources have been reported, but there are no studies on process optimization for the production of these recombinant chitin deacetylases. The present study used the central composite design of response surface methodology to maximize the recombinant bacterial chitin deacetylase (BaCDA) production in E. coli Rosetta pLysS. The optimized process conditions were 0.061% glucose concentration, 1% lactose concentration, an incubation temperature of 22 °C, an agitation speed at 128 rpm, and 30 h of fermentation. At optimized conditions, the expression due to lactose induction was initiated after 16 h of fermentation. The maximum expression, biomass, and BaCDA activity were recorded 14 h post-induction. At the optimized condition, the BaCDA activity of expressed BaCDA was increased ~2.39-fold. The process optimization reduced the total fermentation cycle by 22 h and expression time by 10 h post-induction. This is the first study to report the process optimization of recombinant chitin deacetylase expression using a central composite design and its kinetic profiling. Adapting these optimal growth conditions could result in cost-effective, large-scale production of the lesser-explored moneran deacetylase, embarking on a greener route for biomedical-grade chitosan production.

Subbalaxmi Selvaraj

Papers

Microbial Production of Silver Nanoparticles

A critical look at challenges and future scopes of bioactive compounds and their incorporations in the food, energy, and pharmaceutical sector

A Critical Look at Bioproducts Co-cultured Under Solid State Fermentation and Their Challenges and Industrial Applications

Evaluation of model parameters for growth, tannic acid utilization and tannase production in Bacillus gottheilii M2S2 using polyurethane foam blocks as support

Process Evaluation and Kinetics of Recombinant Chitin Deacetylase Expression in E. coli Rosetta pLysS Cells Using a Statistical Technique.