Metal-based nanoparticles have gained tremendous popularity because of their interesting physical, biological, optical, and magnetic properties. These nanoparticles can be synthesized using a variety of different physical, chemical, and biological techniques. The biological means are largely preferred as it provides an environmentally benign, green, and cost-effective route for the biosynthesis of nanoparticles. These bioresources can act as a scaffold, thereby playing the role of reducing as well as capping agents in the biosynthesis of nanoparticles. Medicinal plants tend to have a complex phytochemical constituent such as alcohols, phenols, terpenes, alkaloids, saponins, and proteins, while microbes have key enzymes which can act as reducing as well as stabilizing agent for NP synthesis. However, the mechanism of biosynthesis is still highly debatable. Herein, the present review is directed to give an updated comprehensive overview towards the mechanistic aspects in the biosynthesis of nanoparticles via plants and microbes. Various biosynthetic pathways of secondary metabolites in plants and key enzyme production in microbes have been discussed in detail, along with the underlying mechanisms for biogenic NP synthesis.

Role of plant phytochemicals and microbial enzymes in biosynthesis of metallic nanoparticles.

An endophytic fungal strain isolated from the leaves of Gymnema sylvestre was identified as Pestalotiopsis microspora VJ1/VS1 based on nucleotide sequencing of internal transcribed spacer region (ITS 1-58S-ITS 2) of 18S rRNA gene (NCBI accession number {"type":"entrez-nucleotide","attrs":{"text":"KX213894","term_id":"1027316127","term_text":"KX213894"}}KX213894) In this study, an efficient and ecofriendly approach has been reported for the synthesis of silver nanoparticles (AgNPs) using aqueous culture filtrate of P microspora Ultraviolet-visible analysis confirmed the synthesis of AgNPs by showing characteristic absorption peak at 435 nm Fourier transform infrared spectroscopy analysis revealed the presence of phenolic compounds and proteins in the fungal filtrate, which are plausibly involved in the biosynthesis and capping of AgNPs Transmission electron microscopy (TEM) showed that the AgNPs were spherical in shape of 2–10 nm in size Selected area electron diffraction and X-ray diffraction studies determined the crystalline nature of AgNPs with face-centered cubic (FCC) lattice phase Dynamic light scattering analysis showed that the biosynthesized AgNPs possess high negative zeta potential value of −357 mV Biosynthesized AgNPs were proved to be potential antioxidants by showing effective radical scavenging activity against 2,2′-diphenyl-1-picrylhydrazyl and H2O2 radicals with IC50 values of 7695±296 and 9495±218 µg/mL, respectively The biosynthesized AgNPs exhibited significant cytotoxic effects against B16F10 (mouse melanoma, IC50 =2643±341 µg/mL), SKOV3 (human ovarian carcinoma, IC50 =1624±248 µg/mL), A549 (human lung adenocarcinoma, IC50 =3983±374 µg/mL), and PC3 (human prostate carcinoma, IC50 =2771±289 µg/mL) cells The biosynthesized AgNPs were found to be biocompatible toward normal cells (Chinese hamster ovary cell line, IC50 =43853±42 µg/mL) Cytological observations on most susceptible SKOV3 cells revealed concentration-dependent apoptotic changes that include cell membrane blebbing, cell shrinkage, pyknotic nuclei, karyorrhexis followed by destructive fragmentation of nuclei The results together in this study strongly provided a base for the development of potential and versatile biomedical applications of biosynthesized AgNPs in the near future

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Biogenesis of silver nanoparticles using endophytic fungus Pestalotiopsis microspora and evaluation of their antioxidant and anticancer activities.

Green synthesis of sodium alginate-silver nanoparticles and their antibacterial activity

Biogenic synthesis of silver nanoparticles (AgNP) was performed at room temperature using Aloe vera plant extract in the presence of ammoniacal silver nitrate as a metal salt precursor. The formation of AgNP was monitored by UV-visible spectroscopy at different time intervals. The shape and size of the synthesized particle were visualized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. These results were confirmed by X-ray powder diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses and further supported by surface-enhanced Raman spectroscopy/Raman scattering (SERS) study. UV-visible spectrum has shown a sharp peak at 420 nm and further evidenced by FTIR peak profile (at 1587.6, 1386.4, and 1076 cm−1 with corresponding compounds). The main band position with SERS was noticed at 1594 cm−1 (C–C stretching vibration). When samples were heated under microwave radiation, AgNP with octahedron shapes with 5–50 nm were found and this method can be one of the easier ways to synthesis anisotropic AgNP, in which the plant extract plays a vital role to regulate the size and shape of the nanoparticles. Enhanced antibacterial effects (two- to fourfold) were observed in the case of Aloe vera plant protected AgNP than the routinely synthesized antibiotic drugs. Shape and size-controlled synthesis of silver nanoparticles using Aloe vera plant extract

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Shape- and Size-Controlled Synthesis of Silver Nanoparticles Using Aloe vera Plant Extract and Their Antimicrobial Activity.

Eco-friendly microwave-assisted green and rapid synthesis of well-stabilized gold and core-shell silver-gold nanoparticles.

Microwave-assisted synthesis of silver nanoparticles using sodium alginate and their antibacterial activity

Fluorescent textile fibres (FTFs) are widely used in many industrial fields. However, in addition to fibres with good fluorescence, fibres with excellent colour controllability, structural stability and appropriate mechanical strength still need to be developed. In this work, CdTe/alginate composite FTFs are prepared by taking advantage of the interactions between CdTe nanocrystals (NCs) and alginate macromolecules via a wet-spinning machine with a CaCl₂ aqueous solution as the coagulation bath. CdTe NCs were chemically fixed in the fibre due to the interactions among surface ligands, macromolecules and coagulators (calcium ions), which ensured the excellent dispersity and good stability of the fibres. Forster resonance energy transfer (FRET) between NCs in the fibre was found to be restricted, which means that the emission colour of the fibres was totally controllable and could be predicted. Other properties of alginate fibres, such as flame retardance and mechanical strength, were also well preserved in the fluorescent fibres. Finally, FTFs showed good selectivity toward trace Hg2+ ions over other metallic ions, and the detection could be identified by the naked eye.

https://www.mdpi.com/2079-4991/9/4/570/pdf

Preparation of CdTe/Alginate Textile Fibres with Controllable Fluorescence Emission through a Wet-Spinning Process and Application in the Trace Detection of Hg2+ Ions.

Study on the mechanical and flame retardant properties of a novel carrageenan fiber-CAF-K,Al

In this study, sodium alginate (SA) nanofibres were obtained by electrospinning via the assistance of traditional poly(ethyl oxide) (PEO) and dimethyl sulfoxide (DMSO) with a high SA/PEO ratio of up to 94:6. However, surfactants with more or less toxicities were replaced by nontoxic and fluorescent carbon dots (CDs) to improve spinnability. Experimental details were conducted by fixing the ratio of SA/PEO to 90:10. Then, the electrospinning products of solutions with different compositions were observed with scanning electron microscopy. Properties such as conductivity, surface tension and rheology of the solutions were investigated to determine the key influencing factors. Moreover, since CDs have excellent fluorescence properties, the fluorescent properties of the nanofibre membrane that was blended with CDs were then collected. In addition, in vitro cytotoxicity assessment of the nanofibres were conducted to evaluate the toxicities and biocompatibility.

Cunzhen Geng

Papers

Microwave-assisted synthesis of silver nanoparticles using sodium alginate and their antibacterial activity

Preparation of CdTe/Alginate Textile Fibres with Controllable Fluorescence Emission through a Wet-Spinning Process and Application in the Trace Detection of Hg2+ Ions.

Study on the mechanical and flame retardant properties of a novel carrageenan fiber-CAF-K,Al

Electrospinning Highly Concentrated Sodium Alginate Nanofibres without Surfactants by Adding Fluorescent Carbon Dots.

Study on the flame retardant property and the pyrolysis process of a novel potassium-ferric carrageenan fiber