During the last decade, metal nanoparticles (MtNPs) have gained immense popularity due to their characteristic physicochemical properties, as well as containing antimicrobial, anti-cancer, catalyzing, optical, electronic and magnetic properties. Primarily, these MtNPs have been synthesized through different physical and chemical methods. However, these conventional methods have various drawbacks, such as high energy consumption, high cost and the involvement of toxic chemical substances. Microbial flora has provided an alternative platform for the biological synthesis of MtNPs in an eco-friendly and cost effective way. In this article we have focused on various microorganisms used for the synthesis of different MtNPs. We also have elaborated on the intracellular and extracellular mechanisms of MtNP synthesis in microorganisms, and have highlighted their advantages along with their challenges. Moreover, due to several advantages over chemically synthesized nanoparticles, the microbial MtNPs, with their exclusive and dynamic characteristics, can be used in different sectors like the agriculture, medicine, cosmetics and biotechnology industries in the near future.

The medicinal importance of a novel plant Olax nana Wall. ex Benth. (family: Olacaceae) was revealed for the first time via HPLC-DAD finger printing, qualitative phytochemical analysis, antioxidant, cholinesterase, and α-glucosidase inhibitory assays. The crude methanolic extract of O. nana (ON-Cr) was subjected to qualitative phytochemical analysis and HPLC-DAD finger printing. The antioxidant potential of ON-Cr was assessed via 1,1-diphenyl,2-picrylhydrazyl (DPPH), 2,2-azinobis[3-ethylbenzthiazoline]-6-sulfonic acid (ABTS) and hydrogen peroxide (H2O2) free radical scavenging assays. Furthermore, acetylcholinesterase (AChE) & butyrylcholinesterase (BChE) inhibitory activities were performed using Ellman’s assay, while α- glucosidase inhibitory assay was carried out using a standard protocol. The qualitative phytochemical analysis of ON-Cr revealed the presence of secondary metabolites like alkaloids, flavonoids, tannins, sterols, saponins and terpenoids. The HPLC-DAD finger printing revealed the presence of 40 potential compounds in ON-Cr. Considerable anti-radical activities was revealed by ON-Cr in the DPPH, ABTS and H2O2 free radical scavenging assays with IC50 values of 71.46, 72.55 and 92.33 μg/mL, respectively. Furthermore, ON-Cr showed potent AChE and BChE inhibitory potentials as indicated by their IC50 values of 33.2 and 55.36 μg/mL, respectively. In the α-glucosidase inhibition assay, ON-Cr exhibited moderate inhibitory propensity with an IC50 value of 639.89 μg/mL. This study investigated Olax nana for the first time for detailed qualitative phytochemical tests, HPLC-DAD finger printing analysis, antioxidant, anticholinesterase and α-glucosidase inhibition assays. The antioxidant and cholinesterase inhibitory results were considerable and can provide scientific basis for further studies on the neuroprotective and anti-Alzheimer’s potentials of this plant. ON-Cr may further be subjected to fractionation and polarity guided fractionation to narrow down the search for isolation of bioactive compounds.

Sageretia thea (Osbeck.) was used as an effective chelating agent for the biosynthesis of iron oxide nanoparticles (IONP's) and extensively characterized through XRD, FTIR, Raman spectroscopy, Energy Dispersive Spectroscopy, HR-SEM/TEM and SAED. Antibacterial assays against five human pathogenic bacterial strains were carried out and minimum inhibitory concentrations were calculated. Pseudomonas aeruginosa (MIC: 7.4 µg/mL) was the most susceptible strain to biosynthesized IONPs. All of the fungal strains showed susceptibility to the IONPs. MTT cytotoxic assay was carried out against the promastigote and amastigote cultures of Leishmania tropica and their IC50 values were calculated as 17.2 and 16.75 µg/mL. The cytotoxic potential was further assessed using brine shrimps, and the IC50 was calculated as 16.46 µg/mL. Moderate antioxidant activities were reported. Human RBCs and macrophages were found to be biocompatible with biogenic IONPs (IC50 > 200 µg/mL). GRAPHICAL ABSTRACT

NiO nanoparticles are biosynthesized using Sageretia thea (Osbeck.) aqueous leave extracts and their biological activities are reported. Nanoparticles (∼18 nm) were characterized through XRD, ATR-FTIR, EDS, SAED, HR-SEM/TEM and Raman spectroscopy. Antibacterial activity was investigated against six pathogenic bacterial strains (gram positive and gram negative) and their corresponding minimum inhibitory concentrations (MICs) were calculated. UV-exposed nanoparticles were investigated to have reduced MICs relative to the NiO nanoparticles have not been exposed to UV. Moderate linear fungal growth inhibition was observed while Mucor racemosus (percentage inhibition 64% ± 2.30) was found to be most susceptible. Cytotoxicity was confirmed using brine shrimps lethality assay (IC₅₀ 42.60 μg/ml). MTT cytotoxicity was performed against Leishmania tropica-KWH23 promastigotes and amastigotes revealed significant percentage inhibition across the applied concentrations. IC₅₀ values were calculated as 24.13 μg/ml and 26.74 μg/ml for the promastigote and amastigote cultures of Leishmania tropica. NiO nanoparticles were found. Moderate, antioxidant potential was concluded through assays like DPPH, TAP and TAC. Furthermore, protein kinase inhibition and alpha amylase inhibition is also reported. Graphical Abstract

Aim: To investigate the physical and biological properties of bioinspired zinc oxide (ZnO) nanoparticles via aqueous leaf extracts of Sageretia thea. Experimental: Nanoparticles of size approximately 12.4 nm were extensively characterized. In vitro antimicrobial, cytotoxic, biocompatible and enzyme inhibition assays were performed. Results: Significant antimicrobial activities with and without UV illumination are reported. Bioinspired ZnO nanoparticles were found effective against fungal strains. MTT assay was performed to check the leishmanicidal activity against promastigotes (IC50: 6.2 μg/ml) and amastigotes (IC50: 10.87 μg/ml) of Leishmania tropica. Brine shrimp lethality was also indicated by bioinspired ZnO nanoparticles (IC50: 21.29 μg/ml). Conclusion: Hemocompatible nature of bioinspired nanoparticles was revealed. Furthermore, the antioxidant activities were performed. In addition, significant protein kinase while insignificant alpha amylase inhibition were recorded. Graphical abstract