Nanotechnology is a new and emerging technology with wealth of applications. It involves the synthesis and application of materials having one of the dimensions in the range of 1-100 nm. A wide variety of physico-chemical approaches are being used these days for the synthesis of nanoparticles (NPs). However, biogenic reduction of metal precursors to produce corresponding NPs is eco-friendly, less expensive, free of chemical contaminants for medical and biological applications where purity of NPs is of major concern. Biogenic reduction is a "Bottom Up" approach similar to chemical reduction where a reducing agent is replaced by extract of a natural products with inherent stabilizing, growth terminating and capping properties. Furthermore, the nature of biological entities in different concentrations in combination with reducing organic agents influence the size and shape of NPs. Present review focuses on microbes or plants based green synthesis of Ag, Au, Cu, Fe, Pd, Ru, PbS, CdS, CuO, CeO2, Fe3O4, TiO2, and ZnO NPs and their potential applications.

Green synthesis of nanoparticles and its potential application.

Nanotechnology is a developing branch of pharmaceutical sciences wherein the particles extend in nanosizes and turn out to be more responsive when contrasted with their unique counter parts. In the past numerous years, the utilization of synthetic concoctions and physical strategies were in mould; however, the acknowledgment of their toxic impacts on human well-being and condition influenced serious world view for the researchers. Presently, green synthesis is the watch word for the combination of nanoparticles (NPs) by plants or their metabolites. This innovation is particularly compensating as far as decreasing the poisonous quality caused by the conventionally integrated NPs. In this review, we cover the perspectives by which metal particles can be integrated from green methods in the perspective of green methods utilized in the NPs combination. In the green strategies, plant metabolites and natural substances are utilized to orchestrate the NPs for the pharmaceutical and other applications. Some characterization methods are also reviewed along with applications of NPs.

Advances in green synthesis of nanoparticles

Metal oxide nanoparticles as antimicrobial agents: a promise for the future

In recent years, the progress of efficient green chemistry approaches for the fabrication of commercially viable noble metallic nanoparticles has become a major focus of researchers. The present review has focused on the various plant-mediated nanoparticle fabrication approaches, with brief discussions on the categories of various plant-mediated synthesis approaches and mechanistic aspects of plant-mediated nanoparticle synthesis. The review also focused on the commercial applications of plant-mediated noble metal nanoparticles. Significant remarks on the limitations of plant-mediated fabrication approaches with prospective future direction are also examined.

Noble Metal Nanoparticles: Plant-Mediated Synthesis, Mechanistic Aspects of Synthesis, and Applications

In recent years, zinc oxide nanoparticles (ZnO NPs) have gained tremendous attention attributed to their unique properties. Notably, evidence has shown that zinc is an important nutrient in living organisms. As such, both prokaryotes and eukaryotes including bacteria, fungi and yeast are exploited for the synthesis of ZnO NPs by using microbial cells or enzyme, protein and other biomolecules compounds in either an intracellular or extracellular route. ZnO NPs exhibit antimicrobial properties, however, the properties of nanoparticles (NPs) are depended upon on their size and shape, which make them specific for various applications. Nevertheless, the desired size and shape of NPs can be obtained through the optimization process of microbes mediated synthesis by manipulating their reaction conditions. It should be noted that ZnO NPs are synthesized by various chemical and physical methods. Nonetheless, these methods are expensive and not environmentally friendly. On that account, the microbes mediated synthesis of ZnO NPs have rapidly evolved recently where the microbes are cleaner, eco-friendly, non-toxic and biocompatible as the alternatives to chemical and physical practices. Moreover, zinc in the form of NPs is more effective than their bulk counterparts and thus, they have been explored for many potential applications including in animals industry. Notably, with the advent of multi-drug resistant strains, ZnO NPs have emerged as the potential antimicrobial agents. This is mainly due to their superior properties in combating a broad spectrum of pathogens. Moreover, zinc is known as an essential trace element for most of the biological function in the animal’s body. As such, the applications of ZnO NPs have been reported to significantly enhance the health and production of the farm animals. Thus, this paper reviews the biological synthesis of ZnO NPs by the microbes, the mechanisms of the biological synthesis, parameters for the optimization process and their potential application as an antimicrobial agent and feed supplement in the animal industry as well as their toxicological hazards on animals.

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Microbial synthesis of zinc oxide nanoparticles and their potential application as an antimicrobial agent and a feed supplement in animal industry: a review

Synthesis of cerium oxide nanoparticles using Gloriosa superba L. leaf extract and their structural, optical and antibacterial properties

This study reveals the synthesis of spherical gold nanoparticles (Au NPs) using aqueous fruit extract of Terminalia arjuna, which contains tannin, terpenoid, saponins, flavonoids, glycosides and polyphenolic compounds. The synthesized Au NPs were characterized by UV–visible spectroscopy (UV–vis), Fourier transform infrared (FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), dynamic light scattering (DLS) and zeta potential (ZP) analyses. UV–visible spectra of the fruit extract containing Au NPs showed a surface plasmon resonance peak at 523 nm. FTIR analysis was performed to analyze the biomolecules responsible for the reduction of Au NPs. FTIR analysis clearly showed that Au NPs were capped with plant compounds. The EDX analysis was used to identify the elemental composition of the synthesized Au NPs. The high crystallinity of Au NPs with a face-centered cubic phase is evident to XRD patterns. AFM and TEM observations revealed that synthesized Au NPs were spherical shape with the range 20–50 nm. DLS measurement revealed that Au NPs were obtained in the average size of 25 nm and it is found to be stable at 21.9 mV through ZP analysis. The synthesized Au NPs were investigated for its antibacterial activity. By contrast, Au NPs did not show any antibacterial activity against Gram-positive and Gram-negative bacteria. The Au NPs were treated with two different concentrations (500 and 1,000 μM) of Gloriosa superba seeds. Au NPs exposure at 1,000 μM concentration has most significant effect on seed germination rate and vegetative growth of G. superba. This is the first report on Au NPs as a biocompatibility material to enhance the seed yield of this endangered medicinal plant.

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Green synthesis of gold nanoparticles from fruit extract of Terminalia arjuna , for the enhanced seed germination activity of Gloriosa superba

Cerium oxide nanoparticles (CeO2 NPs) were synthesized using Aspergillus niger culture filtrate. The mycosynthesized CeO2 NPs were characterized by UV–Visible (UV–Vis), Fourier Transform Infrared (FT-IR), X-ray diffraction (XRD), Micro Raman, Thermogravimetric/Differential Thermal Analysis (TG/DTA), Photoluminescence, and Transmission Electron Microscopy (TEM) analyses. UV–Vis spectrum exhibited a corresponding absorption peak for CeO2 NPs at 296 nm, and the functional groups present in the fungal filtrate responsible for the synthesis of NPs were analyzed by FT-IR. The further characterization of the mycosynthesized CeO2 NPs revealed particles of the cubic structure and spherical shape, with the particle sizes ranging from 5 to 20 nm. The antibacterial activity of CeO2 NPs was examined in respect of two Gram-positive (G+) bacteria (Streptococcus pneumoniae, Bacillus subtilis) and two Gram-negative (G−) bacteria (Proteus vulgaris, Escherichia coli) by disk diffusion method. The test results for CeO2 NPs at a concentration of 10 mg/mL showed higher activities on the zone of inhibition of up to 10.67 ± 0.33 and 10.33 ± 0.33 mm against Streptococcus pneumonia and Bacillus subtilis, respectively, The CeO2 NPs caused 100 % mortality on first instar of Aedes aegypti at 0.250 mg/L concentration after 24-h exposure. The mycosynthesis of CeO2 NPs is a simple, cost-effective and eco-friendly approach and it will also potentially helpful to control pathogenic bacteria and dengue vector.

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Mycogenesis of cerium oxide nanoparticles using Aspergillus niger culture filtrate and their applications for antibacterial and larvicidal activities

Green synthesis is one of the rapid, reliable, and best routes for the synthesis of silver nanoparticles (Ag NPs). The current study revealed that the aqueous leaf extract of Pterocarpus santalinus, which contains steroids, saponins, tannins, phenols, triterpenoids, flavonoids, glycosides, and glycerides, is found to be responsible for bioreduction during the synthesis of spherical Ag nanoparticles. The formed Ag NPs were characterized by ultraviolet-visible (UV-vis), Fourier transform-infrared (FT-IR), X-ray diffraction (XRD), atomic force microscopy (AFM), energy-dispersive X-ray spectroscopy (EDX), and scanning electron microscopy (SEM) analysis. UV-vis spectra of the aqueous medium containing silver nanoparticles showed a surface plasmon resonance peak at 418 nm. FT-IR analysis was performed to analyze the biomolecules responsible for the reduction of Ag NPs. XRD results confirmed the presence of silver nanoparticles with face-centered cubic structure. The EDX analysis showed the completed inorganic composition of the synthesized Ag NPs. AFM analysis exemplified the results of particle sizes (41 nm). The calculated crystallite sizes are in the range of 20 to 50 nm, and the spherical nature of the Ag NPs was ascertained by SEM. The synthesized Ag NPs exhibited good antibacterial potential against gram-positive and gram-negative bacterial strains. The zone of inhibition effect of antibacterial activity depends upon the concentration of Ag NPs.

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Phytosynthesis of silver nanoparticles using Pterocarpus santalinus leaf extract and their antibacterial properties

This work reports an ecofriendly approach for the synthesis of Ruthenium nanoparticles (Ru NPs) using aqueous leaf extract of Gloriosa superba. G. superba contains cholidonic, superbine, colchicine, gloriosol, phy- tosterils and stigmasterin, which are found to be responsi- ble for the bio-reduction of Ru NPs. The synthesized Ru NPs were characterized using UV-Vis spectroscopy, Fluorescence spectra, FTIR, XRD, SEM and EDX analy- ses. UV-Vis spectra of the aqueous medium containing Ru NPs showed a gradual decrease of the absorbance peak observed at 494 nm. Fluorescence spectra of Ru NPs emission (kem) exhibited at 464 nm are attributed to the Ru=N p bonds transition. The biomolecules responsible for the reduction of Ru NPs were analyzed by FTIR. XRD results confirmed the presence of Ru NPs with hexagonal crystal structure. The calculated crystallite sizes using Scherrer formula are in the range from 25 to 90 nm. Scanning electron microscopy ascertained spherical nature of the Ru NPs. The EDX analysis showed the complete elemental composition of the synthesized Ru NPs. The synthesized Ru NPs exhibited good antibacterial perfor- mance against gram-positive and gram-negative bacterial strains, which was studied using standard disc diffusion method. The synthesis of Ru NPs by this method is rapid, facile and can be used for various applications.

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S. Gowri

Papers

Synthesis of cerium oxide nanoparticles using Gloriosa superba L. leaf extract and their structural, optical and antibacterial properties

Green synthesis of gold nanoparticles from fruit extract of Terminalia arjuna , for the enhanced seed germination activity of Gloriosa superba

Mycogenesis of cerium oxide nanoparticles using Aspergillus niger culture filtrate and their applications for antibacterial and larvicidal activities

Phytosynthesis of silver nanoparticles using Pterocarpus santalinus leaf extract and their antibacterial properties

Antibacterial activity of ruthenium nanoparticles synthesized using Gloriosa superba L. leaf extract