Synthesis of metal nanoparticles using plant extracts is one of the most simple, convenient, economical, and environmentally friendly methods that mitigate the involvement of toxic chemicals. Hence, in recent years, several eco-friendly processes for the rapid synthesis of silver nanoparticles have been reported using aqueous extracts of plant parts such as the leaf, bark, roots, etc. This review summarizes and elaborates the new findings in this research domain of the green synthesis of silver nanoparticles (AgNPs) using different plant extracts and their potential applications as antimicrobial agents covering the literature since 2015. While highlighting the recently used different plants for the synthesis of highly efficient antimicrobial green AgNPs, we aim to provide a systematic in-depth discussion on the possible influence of the phytochemicals and their concentrations in the plants extracts, extraction solvent, and extraction temperature, as well as reaction temperature, pH, reaction time, and concentration of precursor on the size, shape and stability of the produced AgNPs. Exhaustive details of the plausible mechanism of the interaction of AgNPs with the cell wall of microbes, leading to cell death, and high antimicrobial activities have also been elaborated. The shape and size-dependent antimicrobial activities of the biogenic AgNPs and the enhanced antimicrobial activities by synergetic interaction of AgNPs with known commercial antibiotic drugs have also been comprehensively detailed.

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Green synthesis of silver nanoparticles using plant extracts and their antimicrobial activities: a review of recent literature

In the field of nanotechnology, the development of reliable and eco-friendly methods for the synthesis of NPs is crucial. The conventional methods for the synthesis of NPs are costly, toxic, and not ecofriendly. To overcome these issues, natural sources such as plant, bacteria, fungi, and biopolymers have been used to synthesize AgNPs. These natural sources act as reducing and capping agents. The shape, size, and applications of AgNPs are prominently affected by the reaction parameters under which they are synthesized. Accessible distributed data on the synthesis of AgNPs include the impact of different parameters (temperature and pH), characterization techniques (DLS, UV-vis, FTIR, XRD, SEM, TEM and EDX), properties and their applications. This review paper discusses all the natural sources such as plants, bacteria, fungi, and biopolymers that have been used for the synthesis of AgNPs in the last ten years. AgNPs synthesized by green methods have found potential applications in a wide spectrum of areas including drug delivery, DNA analysis and gene therapy, cancer treatment, antimicrobial agents, biosensors, catalysis, SERS and magnetic resonance imaging (MRI). The current limitations and future prospects for the synthesis of inorganic nanoparticles by green methods are also discussed herein.

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Facile green synthesis and applications of silver nanoparticles: a state-of-the-art review

A large number of metallic nanoparticles have been successfully synthesized by using different plant extracts and microbes including bacteria, fungi viruses and microalgae. Some of these metallic nanoparticles showed strong antimicrobial activities against phytopathogens. Here, we summarized these green-synthesized nanoparticles from plants and microbes and their applications in the control of plant pathogens. We also discussed the potential deleterious effects of the metallic nanoparticles on plants and beneficial microbial communities associated with plants. Overall, this review calls for attention regarding the use of green-synthesized metallic nanoparticles in controlling plant diseases and clarification of the risks to plants, plant-associated microbial communities, and environments before using them in agriculture.

Advancements in Plant and Microbe-Based Synthesis of Metallic Nanoparticles and Their Antimicrobial Activity against Plant Pathogens.

Nanoscale metals are widely used in many fields such as environment, medicine, and engineering that synthesis of nanoscale metals is a timely topic. At present, nanoscale metals are mainly synthesized by chemical methods that have unintended effects such as environmental pollution, large energy consumption, and potential health problems. In response to these challenges, green synthesis, which uses plant extracts instead of industrial chemical agents to reduce metal ions, has been developed. Green synthesis is more beneficial than traditional chemical synthesis because it costs less, decreases pollution, and improves environmental and human health safety. In this review, current developments in the green synthesis of nanoparticles of gold (Au NPs), silver (Ag NPs), palladium (Pd NPs), copper (Cu NPs), and iron and its oxide (Fe NPs) were evaluated. Major findings reveal the complexity in geographical and seasonal distributions of plants and their compositions that green synthesis is limited by time and place of production as well as issues with low purity and poor yield. However, considering current environmental problems and pollution associated with chemical synthesis, green synthesis offers alternative development prospects and potential applications. 

Green synthesis of nanoparticles: Current developments and limitations

Carbohydrate and protein based biopolymeric nanoparticles: Current status and biotechnological applications

Green synthesis of silver nanoparticles makes use of plant constituents, like carbohydrates, fats, enzymes, flavonoids, terpenoids, polyphenols, and alkaloids, as reducing agents to synthesize silver nanoparticles. The present study for the first time utilized seed extract of Tectona grandis (teak) for reduction of 1 mM silver nitrate solution to silver nanoparticles. The method proved to be very simple, cost-efficient, and convenient. Synthesis of nanoparticles was confirmed by visual detection in which the colorless solution gets changed to a brown-colored solution. Further characterization was done by UV-visible spectroscopy, XRD, FTIR analysis, SEM/EDS, FESEM, and TEM. Size of silver nanoparticles was found to be 10–30 nm approximately as determined by transmission electron microscopy (TEM). Energy-dispersive spectra (EDS) revealed that nanoparticles contain silver in its pure form. Well diffusion method showed the antimicrobial effect of AgNPs on different microorganisms with the zone of inhibition of 16 mm for Staphylococcus aureus, 12 mm for Bacillus cereus, and 17 mm for E. coli when 50 μg of AgNPs was used. Minimum inhibitory concentration was found to be 5.2, 2.6, and 2.0 μg/ml for Bacillus cereus, Staphylococcus aureus, and E. coli respectively. Mode of action of antimicrobial activity of nanoparticles was investigated by determining leakage of reducing sugars and proteins, suggesting that AgNPs were able to destroy membrane permeability.

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Green synthesis of silver nanoparticles from Tectona grandis seeds extract: characterization and mechanism of antimicrobial action on different microorganisms

Microalgae have been reported to exhibit mutualistic interactions with other microorganisms like bacteria, filamentous fungi, and yeast and help each other co-exist. The potential of microalgae to perform photosynthesis and accumulate lipids make them suitable candidates for lipid production. Biofuel production from various single oleaginous microorganisms is already in practice. However, the high cost of biomass harvesting, extraction of lipids, and contamination issues are significant challenges of biofuel bioprocess commercialization. Recent microalgal co-culture studies showed considerable potential for easy biomass harvesting and reduction in overall energy consumption cost. Therefore, microalgal co-culture could be an alternative to overcome these constraints and enhance biomass and lipid production. Additionally, the integration of the nutrient sequestration process from potential agro-industrial wastewater using microalgal co-culture can reduce the cost of the substrate requirement for cultivation as well as ecological load. The co-culture in wastewater has shown excellent total phosphate removal efficiencies by microalgae Chlorella sorokiniana and yeast Rhodotorula glutinis, nitrogen removal by microalgae C. sorokiniana with activated sludge, and ammonium-nitrogen removal by C. vulgaris and fungi Aspergillus sp. co-culture. This review summarized the current advances towards biofuel and its value-added production from various microalgae co-culture and compared it with monoculture fermentation. It also includes some critical challenges of co-culturing for the economically viable bioprocess development for biofuel production. Furthermore, techno-economic analysis and life-cycle assessment of co-culture technology were also discussed for biofuel production feasibility from microalgal co-culture.

Microalgal Co-cultivation for Biofuel Production and Bioremediation: Current Status and Benefits

Wine is consumed globally as an alcoholic beverage with an increasing demand that has reached 243 million hectoliters. According to the existing statistics, as much as 5 tons of solid waste is produced per hectare per year during the process of cultivation and harvesting of grapes. Wineries across the world generate large volumes of waste and other by-products, these include grape stalks, pomace/marc, and wine lees. This waste needs to be biovalorized and treated before its disposal into landfills and wastewater streams to ensure minimum environmental damage. Winery waste is highly rich in lignocellulosic compounds and thus serves as a promising feedstock for the production of renewable energy. This waste contains bioactive compounds like phenolics, flavonoids, tannins, coumarins, and antioxidants having numerous health benefits and can be used as additives for food and cosmetic products. Biovalorization of winery waste proves to be an innovative strategy to reuse, recycle, and recover potentially useful residues from this waste and will reduce the dependence of the current manufacturing industries on the starting raw materials. Microorganisms produce industrially important organic acids like tartaric acid, lactic acid, and enzymes by the fermentation of the sugars present in the winery waste. There is a necessity to exploit the potential of microorganisms for the production of commercially important compounds and implement efficient extraction techniques like pulsed electric field, supercritical fluid extraction, and high voltage electric discharge for their high recoveries. Thermal conversion of this biomass is both economically and energetically expensive; biochemical procedures have great potential to convert winery waste into high-value products. This chapter focuses on the minimization of environmental hazards of winery waste by its efficient utilization for the production of phytochemicals and potential biofuels through biovalorization.

Jyoti Rani

Papers

Green synthesis of silver nanoparticles from Tectona grandis seeds extract: characterization and mechanism of antimicrobial action on different microorganisms

Microalgal Co-cultivation for Biofuel Production and Bioremediation: Current Status and Benefits

Biovalorization of winery industry waste to produce value-added products

Antibiotics in anaerobic digestion: Investigative studies on digester performance and microbial diversity.

Smart solution for leaf stress detection and classification a research pattern