Green synthesis of biogenic silver nanomaterials using Raphanus sativus extract, effects of stabilizers on the morphology, and their antimicrobial activities

Non-conventional, burnt Shorea robusta leaf extract mediated green synthesis of zinc oxide nanoparticles and facile removal of eriochrome black T dye from water

The present study evaluates the synthesis of zinc oxide nanoparticles (ZnO NPs) using water extract of Sal leaves (Shorea Robusta) for efficient removal of Eriochrome black-T from the water and wastewater. The material is characterized using FESEM, FTIR, EDX, pHzpc, XRD, BET, and TGA analysis. XRD confirmed the synthesis of ZnO with an average crystallite size of 35.24 nm a surface area of 95.939 m2/g and a pore volume of 0.280 cm3/g. The pHzpc of the material is 7.45. The study evaluates the effects of contact time (0-100 min), pH (3-10), concentration (10-50 mg/L), and temperature (298-328K). The Langmuir isotherm model (R2 = 0.993) and pseudo-second-order kinetic model (R2 = 0.998) were found to be the best-fit models. The maximum uptake capacity is 265.554 mg/g. The interaction is spontaneous (ΔG° -12.889 to-14.898 kJ/mol), endothermic ΔH° (4.290-14.216 kJ/mol) with an increase in spontaneity at the solid-liquid junction. The dye-loaded ZnO NPs were successfully regenerated in dilute NaOH solution and 1:1 methanol water, achieving regeneration efficiencies of 78% and 60%, respectively. The reusability of the ZnO NPs was ascertained for up to three consecutive cycles.

Optimization of Synthesis of Silver Nanoparticles Conjugated with Lepechinia meyenii (Salvia) Using Plackett-Burman Design and Response Surface Methodology—Preliminary Antibacterial Activity

In the present investigation, an ethanolic fraction (EF) of Lepechinia meyenii (salvia) was prepared and fractionated by gradient column chromatography, and the main secondary metabolites present in the EF were identified by HPLC-MS. Silver nanoparticles (AgNPs) were synthesized and conjugated with the EF of Lepechinia meyenii (salvia). The AgNPs synthesis was optimized using Plackett-Burman design and response surface methodology (RSM), considering the following independent variables: stirring speed, synthesis pH, synthesis time, synthesis temperature and EF volume. The AgNPs synthesized under the optimized conditions were characterized by UV visible spectroscopy (UV-VIS), Fourier Transform Infrared Spectroscopy (FT-IR), Dynamic Light Scattering (DLS) and Scanning Transmission Electron Microscopy (STEM). The antibacterial activity of the AgNPs against Staphylococcus aureus (ATCC® 25923) was evaluated. The following flavonoids were identified: rosmarinic acid, diosmin and hesperetin-7-O-rutinoside. The optimized conditions for the synthesis of nanoparticles were pH 9.45, temperature 49.8 °C, volume of ethanolic fraction 152.6 µL and a reaction time of 213.2 min. The obtained AgNPs exhibited an average size of 43.71 nm and a resonance plasmon of 410–420 nm. Using FT-IR spectroscopy, the disappearance of the peaks between 626.50 and 1379.54 cm−1 was evident with the AgNPs, which would indicate the participation of these functional groups in the synthesis and protection of the nanoparticles. A hydrodynamic size of 47.6 nm was obtained by DLS, while a size of 40–60 nm was determined by STEM. The synthesized AgNPs conjugated with the EF showed a higher antibacterial activity than the EF alone. These results demonstrate that the AgNPs synthesized under optimized conditions conjugated with the EF of the Lepechinia meyenii (salvia) presented an increased antibacterial activity.

Immobilization of GOx Enzyme on SiO2-Coated Ni-Co Ferrite Nanocomposites as Magnetic Support and Their Antimicrobial and Photocatalytic Activities

The present study used a sol-gel auto-combustion approach to make silica (SiO2)-coated Ni-Co ferrite nanocomposites that would be used as a platform for enzyme immobilization. Using glutaraldehyde as a coupling agent, glucose oxidase (GOx) was covalently immobilized on this magnetic substrate. X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), and fourier transform infrared spectroscopy (FTIR) was used to determine the structural analysis and morphology of Ni-Co ferrite/SiO2 nanocomposites. FTIR spectra confirmed the binding of GOx to Ni-Co ferrite/SiO2 nanocomposites, with a loading efficiency of around 85%. At alkaline pH and higher temperature, the immobilized GOx enzyme exhibited increased catalytic activity. After 10 times of reuses, it still had 69% catalytic activity. Overall, the immobilized GOx displayed higher operational stability than the free enzyme under severe circumstances and was easily recovered by magnetic separation. With increased doping concentration of the nanocomposites, the photocatalytic activity was assessed using a degradation process in the presence of methylene blue dye under UV light irradiation, which revealed that the surface area of the nanocomposites with increased doping concentration played a significant role in improving photocatalytic activity. The antibacterial activity of Ni-Co ferrite/SiO2 nanocomposites was assessed using the agar well diffusion method against Escherichia coli, a gram-negative bacteria (ATCC 25922). Consequently, it was revealed that doping of Ni2+ and Co2+ in Fe2O4/SiO2 nanocomposites at varied concentrations improved their antibacterial properties.

Deciphering the Kinetic Study of Sodium Dodecyl Sulfate on Ag Nanoparticle Synthesis Using Cassia siamea Flower Extract as a Reducing Agent

Silver nanoparticles (Ag NPs) were synthesized using Cassia siamea flower petal extract (CSFE) as a reducing agent for the first time. In its presence and absence, the correlative effects of the anionic surface-active agent sodium dodecyl sulfate (SDS) were studied with respect to the development and texture of Ag NPs. Under different reagent compositions, the Ag NPs were inferred by localized surface plasmon resonance peaks between 419 and 455 nm. In the absence of SDS, there was a small eminence at 290 and around 350 nm, pointing toward the possibility of irregular polytope Ag NPs, which was confirmed in the transmission electron microscopy images. This elevation vanished beyond the cmc of [SDS], resulting in spherical and oval shaped Ag NPs. The effects of reagent concentrations were studied at 25 °C and around 7 and 9 pH in the absence and presence of SDS, respectively. Also, kinetic studies were performed by UV-visible spectrophotometry. Prodigious effects on shape and size were found under different synthesis conditions in terms of hexagonal, rod-, irregular-, and spherical shaped Ag NPs. Furthermore, the antimycotic activity of the synthesized Ag NPs was established on different Candida strains, and best results were found pertaining Candida tropicalis. The ensuing study impels the control of texture and dispersity for Ag NPs by CSFE and SDS, and the resultant polytope Ag NPs could be a future solution for drug-resistant pathogenic fungi.

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

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.

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

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.

3D hybrid structures based on biomimetic membranes and Caryophyllus aromaticus - "green" synthesized nano-silver with improved bioperformances

The paper describes an innovative bio-design of some hybrid nanoarchitectures containing bioartificial membranes and silver nanoparticles phytogenerated by using a natural extract Caryophyllus aromaticus (cloves) that contains many bioactive compounds. Two kinds of liposomes with and without chlorophyll a (Chla) obtained through thin film hydration method were used to achieve bio-green-generated hybrids by a simple, cost effective bottom-up approach. The characteristic peaks of CE-nAg monitored by UV-Vis absorption have firstly demonstrated the biohybrids formation. The slightly blue shift and fluorescence quenching observed by fluorescence emission spectra highlighted the formation of hybrid systems by biointeraction between lipid vesicles and silver nanoparticles. The incorporation of silver nanoparticles in lipid vesicles resulted in significant changes of FT-IR spectra of liposomes, indicating a reorganization of biomimetic membranes. All the microscopic methods (SEM, AFM and TEM) confirmed the biosynthesis of "green" AgNPs together with associated biohybrids, their spherical and quasi-spherical shapes with nano-scaled size. By TEM assay it was shown that CE-nAg are surrounded by petal like cloud structures that consist of biopolymers like proteins or polysaccharides and other phytochemicals arising from clove extract. EDS spectra confirmed the formation of phyto-nanoAg and also the presence of silver in the biohybrids. In addition, Selected Area Electron Diffraction showed characteristic polycrystalline ring patterns for a cubic structure of the clove-generated AgNPs. The hybrid materials showed efficient physical stability,i.e. ξ value of -28.0 mV (for biohybrids without Chla, BH) and of -31.7 mV (for biohybrids labelled with Chla, Chla-BH), assured by strong electrostatic repulsive forces between particles. The "green" nano-silver particles (CE-nAg) showed remarkable antioxidant activity (AA = 90.2%). The biohybrids loaded with clove-AgNPs proved to be more effective, scavenging about 98.8% of free radicals (in case of Chla-BH), and of 92.6% (in case of BH). The antibacterial effectiveness showed that green AgNPs combine in a synergistic manner the antibacterial properties of clove extract with those of silver, resulting in an enhancement of inhibition diameter, by 20%. Chla-BH proved to be more potent against Escherichia coli, than BH, exhibiting an inhibition diameter of 42 mm. Regarding the in vitro cytotoxicity against tumour cells, the CE-nAg concentration significantly influenced the cell viability, i.e. IC₅₀ was 3.6% (v/v) for HT-29 cells. Chla-BH was more effective against HT-29 cancer cells at the concentrations ranging from 0 to 18% (v/v), when the normal cells were not affected. Clove-generated AgNPs exhibited haemolytic activity against hRBCs, while the biohybrids were haemocompatible. The action mechanism on the two cell lines (mouse fibroblast L929 cells and human colorectal adenocarcinoma HT-29 cells) investigated by fluorescence microscopy demonstrated that CE-nAg killed almost all the cells (94%) through necrosis at a concentration of 33.4% (v/v). The treatment of HT-29 cells with BH resulted in: 71.5% viable cells, 19.5% apoptotic and only 9% necrotic cells, while in the case of Chla-BH treatment, only 77.5% cells were viable, 16% cells were apoptotic and 6.5% were necrotic. In this way, the developed silver-based nanoparticles can represent viable promoters to develop new biohybrids with improved features, e.g. antioxidant and antibacterial effectiveness, haemolytic activity and greater specificity towards tumour cells.

Eco-friendly synthesis of silver and gold nanoparticles with enhanced antimicrobial, antioxidant, and catalytic activities

The present work is emphasised on the bio-fabrication of silver and gold nanoparticles in a single step by a microwave-assisted method using the leaf extract of Synedrella nodiflora as both reducing and stabilising agent. The synthesised nanoparticles are highly stable and show surface plasmon resonance peak at 413 and 535 nm, respectively, for silver and gold nanoparticles in UV-Vis spectrum. The functional group responsible for the reduction of metal ions were obtained from Fourier transform infrared spectroscopy. The crystalline nature of nanoparticles with face-centred cubic geometry was confirmed by the X-ray diffraction and selected area electron diffraction patterns. The morphology and sizes of the silver and gold nanoparticles were obtained from transmission electron microscopy images. The nanoparticles exhibit effective antimicrobial activities against various pathogenic strains. These antimicrobial properties were analysed by employing agar well diffusion method. The nanoparticles show significant antioxidant properties, and it was determined using 2, 2-diphenyl-1-picrylhydrazyl assay. The nanoparticles also show potent catalytic activity in the degradation of anthropogenic pollutant dyes Congo red and eosin Y by excess NaBH4. Thus, the current study demonstrates the potential use of S. nodiflora as a reducing and stabilising agent for the synthesis of silver and gold nanoparticles and their relevance in the field of biomedicine and catalysis.

Green silver nanoparticles from novel Brassicaceae cultivars with enhanced antimicrobial potential than earlier reported Brassicaceae members

In the present study, we report perhaps for the first time the use of novel varieties of Brassica oleracea var. botrytis and Raphanus sativus as potential bioreductant, to synthesize highly stable silver nanoparticles (AgNPs, no aggregation observed for six months), which is a significant finding as plant extract-directed AgNPs are intrinsically unstable and tend to aggregate. The reduction of Ag⁺ to Ag⁰ nanostructures was confirmed using UVVis spectroscopy showing SPR spectra at 400-435 nm. Nanosight and transmission electron microscope (TEM) analysis showed monodisperse spherical AgNPs (4-18 nm). Fourier transform infrared spectroscopy (FTIR) analysis revealed that the polyphenolics and other secondary metabolites including glucosinolates in the aqueous extracts may act as reducing/capping agent for the nanoparticle synthesis. X-ray diffraction (XRD) confirmed the face centered cubic crystalline (fcc) structure of AgNPs. Controlled synthesis of AgNPs was achieved by varying experimental parameters (AgNO₃ concentration, extract volume, pH and temperature). These AgNPs exhibited strong antibacterial activity at significantly lower concentration (5 ppm) against both Gram negative (Escherichia coli, Myroides, Psuedomonas aeruginosa) and Gram positive (Kocuria and Promicromonospora) bacteria. In the present study, the green AgNPs showed (10-30%) better antimicrobial efficacy than chemical AgNPs and AgNPs from other Brassicaceae members. These green AgNPs may have promising application in nano-drug formulation to combat bacterial infections, in future.

Garlic, green tea and turmeric extracts-mediated green synthesis of silver nanoparticles: Phytochemical, antioxidant and in vitro cytotoxicity studies

Phyto-synthesis of silver nanoparticles (AgNPs) was achieved using aqueous garlic, green tea and turmeric extracts, and characterized by different spectroscopic techniques. Phytochemical analysis revealed the presence of rich amount of biochemicals in these extracts, which serve as reducing and capping agents for converting silver nitrate into AgNPs. FT IR spectroscopy confirmed the role of biomolecules in the bioreduction and efficient stabilization of AgNPs. UV-Vis DRS spectra showed a band around 450 nm characteristics of AgNPs. XRD patterns revealed the crystalline nature of the synthesized AgNPs with fcc structure. SEM and TEM analysis revealed the spherical shape of the synthesized AgNPs with an average particle size of 8 nm. EDX analysis confirmed the purity of the synthesized AgNPs with a strong signal at 3.2 keV. The antioxidant activity was assessed by ABTS, DPPH, p-NDA, H₂O₂ and DMSO scavenging assays, in which the AgNPs synthesized using green method showed remarkable activity with respect to the standard antioxidants ascorbic acid and rutin. In vitro cytotoxicity activity was tested on four cancer cell lines such as human breast adenocarcinoma (MCF-7), cervical (HeLa), epithelioma (Hep-2) and lung (A549) along with one normal human dermal fibroblasts (NHDF) cell line. The AgNPs synthesized using turmeric extract exhibits excellent antioxidant and cytotoxicity activity compared to that synthesized using other extracts.

Green synthetic approach for starch capped silver nanoparticles and their antibacterial activity

In this work silver nanoparticles (AgNPs) have been prepared from silver nitrate (AgNO3) precursor using a green synthesis method at room temperature. Starch with its abundance of hydroxyl groups and its biocompatibility was used as a capping and reducing agent. The formation of AgNPs was confirmed by absorption spectroscopy with the surface plasmon resonance peak at 400 nm. The sharp reflection at (111), (200), (220) and (311) was observed by powder X-ray diffraction (XRD), which indicated the presence of cubic phase AgNPs. Transmission electron microscopy (TEM) revealed that the average size of AgNPs were between 0.5 and 4 nm with a spherical shape under optimum conditions. The nanoparticles showed a decrease in size with an increase in precursor concentration as well as the increase in capping agent concentration. The nanoparticles also showed to be bactericidal towards the tested Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria.

Growth of Ag-nanoparticles in an aqueous solution and their antimicrobial activities against Gram positive, Gram negative bacterial strains and Candida fungus

Silver nanoparticles (AgNPs) were synthesized using Ocimum sanctum (Tulsi) leaves aqueous extract as reducing as well as a capping agent in absence and presence of cetyltrimethylammonium bromide (CTAB). The resulting nanomaterials were characterized by UV-visible spectrophotometer, and transmission electron microscope. The UV-Vis spectroscopy revealed the formation of AgNPs at 400-450 nm. TEM photographs indicate that the truncated triangular silver nanoplates and/or spherical morphology of the AgNPs with an average diameter of 25 nm have been distorted markedly in presence of CTAB. The AgNPs were almost mono disperse in nature. Antimicrobial activities of AgNPs were determined by using two bacteria (Gram positive Staphylococcus aureus MTCC-3160), Gram negative Escherichia coli MTCC-450) and one species of Candida fungus (Candida albicans ATCC 90030) with Kirby-Bauer or disc diffusion method. The zone of inhibition seems extremely good showing a relatively large zone of inhibition in both Staphylococcus aureus, Escherichia coli, and Candida albicans strains.