Phoenix dactylifera L. leaf extract phytosynthesized gold nanoparticles; controlled synthesis and catalytic activity

Green synthesized silver nanoparticles from Phoenix dactylifera synergistically interact with bioactive extract of Punica granatum against bacterial virulence and biofilm development

The global rise of antibiotic resistance poses a substantial risk to mankind, underscoring the necessity for alternative antimicrobial options. Developing novel drugs has become challenging in matching the pace at which microbial resistance is evolving. Recently, nanotechnology, coupled with natural compounds, has emerged as a promising solution to combat multidrug-resistant bacteria. In the present study, silver nanoparticles were green-synthesized using aqueous extract of Phoenix dactylifera (variety Ajwa) fruits and characterized by UV-vis spectroscopy, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) coupled with Energy dispersive X-ray analysis (EDX), Transmission electron microscopy (TEM) and Thermogravimetric-differential thermal analysis (TGA-DTA). The in-vitro synergy of green synthesized P. dactylifera silver nanoparticle (PD-AgNPs) with selected antibiotics and bioactive extract of Punica granatum, i.e., ethyl acetate fraction (PGEF), was investigated using checkerboard assays. The most effective synergistic combination was evaluated against the QS-regulated virulence factors production and biofilm of Pseudomonas aeruginosa PAO1 by spectroscopic assays and electron microscopy. In-vivo anti-infective efficacy was examined in Caenorhabditis elegans N2 worms. PD-AgNPs were characterized as spherical in shape with an average diameter of 28.9 nm. FTIR analysis revealed the presence of functional groups responsible for the decrease and stabilization of PD-AgNPs. The signals produced by TGA-DTA analysis indicated the generation of thermally stable and pure crystallite AgNPs. Key phytocompounds detected in bioactive fractions include gulonic acid, dihydrocaffeic acid 3-O-glucuronide, and various fatty acids. The MIC of PD-AgNPs and PGEF ranged from 32 to 128 μg/mL and 250-500 μg/mL, respectively, against test bacterial strains. In-vitro, PD-AgNPs showed additive interaction with selected antibiotics (FICI 0.625-0.75) and synergy with PGEF (FICI 0.25-0.375). This combination inhibited virulence factors by up to 75 % and biofilm formation by 84.87 % in P. aeruginosa PAO1. Infected C. elegans worms with P. aeruginosa PAO1 had a 92.55 % survival rate when treated with PD-AgNPs and PGEF. The combination also reduced the reactive oxygen species (ROS) level in C. elegans N2 compared to the untreated control. Overall, these findings highlight that biosynthesized PD-AgNPs and bioactive P. granatum extract may be used as a potential therapeutic formulation against MDR bacteria.

Catalytic innovations: Improving wastewater treatment and hydrogen generation technologies

The effective reduction of hazardous organic pollutants in wastewater is a pressing global concern, necessitating the development of advanced treatment technologies. Pollutants such as nitrophenols and dyes, which pose significant risks to both human and aquatic health, making their reduction particularly crucial. Despite the existence of various methods to eliminate these pollutants, they are not without limitations. The utilization of nanomaterials as catalysts for chemical reduction exhibits a promising alternative owing to their distinguished catalytic activity and substantial surface area. For catalytically reducing the pollutants NaBH4 has been utilized as a useful source for it because it reduces the pollutants quiet efficiently and it also releases hydrogen gas as well which can be used as a source of energy. This paper provides a comprehensive review of recent research on different types of nanomaterials that function as catalysts to reduce organic pollutants and also generating hydrogen from NaBH4 methanolysis while also evaluating the positive and negative aspects of nanocatalyst. Additionally, this paper examines the features effecting the process and the mechanism of catalysis. The comparison of different catalysts is based on size of catalyst, reaction time, rate of reaction, hydrogen generation rate, activation energy, and durability. The information obtained from this paper can be used to steer the development of new catalysts for reducing organic pollutants and generation hydrogen by NaBH4 methanolysis.

Biogenic synthesis of AuNPs using Solanum virginianum L. and their antibacterial, antioxidant and catalytic applications

Biogenic synthesis of nanoparticles is gaining popularity worldwide because of being ecofriendly as well as economical, with minimal production of hazardous by-products. The present study was targeted to determine the antibacterial, free radical scavenging and catalytic activity of gold nanoparticles synthesized from Solanum virginianum L. (Sv-AuNPs). After addition of auric chloride, the color of aqueous plant extract changed from light yellow to purple-red, indicating the formation of nanoparticles. A strong peak at 536 nm affirmed synthesis of Sv-AuNPs, and negative zeta potential (- 30.7) indicated their being wrapped in anions. They exhibited face-centered cubic and crystalline nature as revealed by X-ray diffraction. Elemental composition of Sv-AuNPs was ascertained by energy-dispersive X-ray spectroscopy, and a sharp peak at 2.2 keV confirmed the presence of gold. The shape of Sv-AuNPs synthesized was spherical with size ranging from 29.1 ± 1 nm to 51.2 ± 0.7 nm. Antibacterial potential was evaluated against E. coli, C. violaceum, K. pneumoniae, P. aeruginosa, B. subtilis, M. smegmatis, and S. aureus and was found to be greater than aqueous plant extract. Sv-AuNPs exhibited antioxidant potential comparable to ascorbic acid, demonstrating their vital role in the prevention of reactive oxygen species related diseases. Apart from their pharmaceutical potential, these nanoparticles also exhibited promising catalytic efficacy. They degraded harmful dyes i.e. 4-nitro phenol (4-NP) and congo red (CR) at a very low concentration of 50 µg/ml. This is the first report on the antibacterial, antioxidant, and catalytic properties of Sv-AuNPs and we hope it will lead the way for nanoparticles multifunctionality.

Graphical abstract

Sustainable Nanomagnetism: Investigating the Influence of Green Synthesis and pH on Iron Oxide Nanoparticles for Enhanced Biomedical Applications

This study comprehensively analyzed green nanomagnetic iron oxide particles (GNMIOPs) synthesized using a green method, investigating their size, shape, crystallinity, aggregation, phase portions, stability, and magnetism. The influence of pH and washing solvents on the magnetic properties of the nanoparticles and their incorporation into PCL membranes was examined for biomedical applications. Polyphenols were utilized at different pH values (1.2, 7.5, and 12.5), with washing being performed using either ethanol or water. Characterization techniques, including XRD, SEM, TEM, FTIR, and VSM, were employed, along with evaluations of stability, magnetic properties, and antioxidant activity. The findings indicate that both pH levels and the washing process exert a substantial influence on several properties of NMIOPs. The particle sizes ranged from 6.6 to 23.5 nm, with the smallest size being observed for GNMIOPs prepared at pH 12.5. Higher pH values led to increased crystallinity, cubic Fe3O4 fractions, and reduced crystalline anisotropy. SEM and TEM analyses showed pH-dependent morphological variations, with increased aggregation being observed at lower pH values. GNMIOPs displayed exceptional magnetic behavior, with the highest saturation magnetization being observed in GNMIOPs prepared at pH 7.5 and 12.5 and subsequently washed with ethanol. The zeta potential measurements indicated a stability range for GNMIOPs spanning from -31.8 to -41.6 mV, while GNMIOPs synthesized under high-pH conditions demonstrated noteworthy antioxidant activity. Furthermore, it was explored how pH and washing solvent affected the morphology, roughness, and magnetic properties of GNMIOP-infused nanofiber membranes. SEM showed irregularities and roughness due to GNMIOPs, varying with pH and washing solvent. TEM confirmed better dispersion with ethanol washing. The magnetic response was stronger with ethanol-washed GNMIOPs, highlighting the influence of pH and washing solvent on membrane characteristics.

Effect of Calcination Temperature and Time on the Synthesis of Iron Oxide Nanoparticles: Green vs. Chemical Method

Nowadays, antioxidants and antibacterial activity play an increasingly vital role in biosystems due to the biochemical and biological reactions that involve free radicals and pathogen growth, which occur in many systems. For this purpose, continuous efforts are being made to minimize these reactions, including the use of nanomaterials as antioxidants and bactericidal agents. Despite such advances, iron oxide nanoparticles still lack knowledge regarding their antioxidant and bactericidal capacities. This includes the investigation of biochemical reactions and their effects on nanoparticle functionality. In green synthesis, active phytochemicals give nanoparticles their maximum functional capacity and should not be destroyed during synthesis. Therefore, research is required to establish a correlation between the synthesis process and the nanoparticle properties. In this sense, the main objective of this work was to evaluate the most influential process stage: calcination. Thus, different calcination temperatures (200, 300, and 500 °C) and times (2, 4, and 5 h) were studied in the synthesis of iron oxide nanoparticles using either Phoenix dactylifera L. (PDL) extract (green method) or sodium hydroxide (chemical method) as the reducing agent. The results show that calcination temperatures and times had a significant influence on the degradation of the active substance (polyphenols) and the final structure of iron oxide nanoparticles. It was found that, at low calcination temperatures and times, the nanoparticles exhibited small sizes, fewer polycrystalline structures, and better antioxidant activities. In conclusion, this work highlights the importance of green synthesis of iron oxide nanoparticles due to their excellent antioxidant and antimicrobial activities.

Biopolymer-Based Films Reinforced with Green Synthesized Zinc Oxide Nanoparticles

Nowadays, biopolymer-based films are being developed as an alternative to conventional plastic-based films, mainly because they are non-toxic, flexible, inexpensive, and widely available. However, they are restricted in their applications due to several deficiencies in their properties. Accordingly, the reinforcement of these materials with nanoparticles/nanofillers could overcome some of their shortcomings, especially those processed by green methods. Green synthesized zinc oxide nanoparticles (ZnO-NPs) are highly suggested to overcome these deficiencies. Therefore, the main aim of this work was to develop different biopolymer-based films from cellulose acetate (CA), chitosan (CH), and gelatin (GE) reinforced with ZnO-NPs prepared by casting, and to assess their different properties. The results show the improvements produced by the incorporation of ZnO-NPs (1% w/w) into the CA, CH, and GE systems. Thus, the water contact angles (WCAs) increased by about 12, 13, and 14%, while the water vapor permeability (WVP) decreased by about 14, 6, and 29%, the water solubility (WS) decreased by about 23, 6, and 5%, and the transparency (T) increased by about 19, 31, and 20% in the CA, CH, and GE systems, respectively. Furthermore, the mechanical properties were enhanced by increasing the ultimate tensile strength (UTS) (by about 39, 13, and 26%, respectively) and Young's modulus (E) (by about 70, 34, and 63%, respectively), thereby decreasing the elongation at the break (ε_max) (by about 56, 23, and 49%, respectively) and the toughness (by about 50, 4, and 30%, respectively). Lastly, the antioxidant properties were enhanced by 34, 49, and 39%, respectively.

Green Synthesis of FexOy Nanoparticles with Potential Antioxidant Properties

Iron oxide nanoparticles (Fe_xO_y-NPs) are currently being applied in numerous high-tech sectors, such as in chemical sectors for catalysis and in the medical sector for drug delivery systems and antimicrobial purposes, due to their specific, unique and magnetic properties. Nevertheless, their synthesis is under continuous investigation, as physicochemical methods are considered expensive and require toxic solvents. Thus, green nanotechnology has shown considerable promise in the eco-biogenesis of nanoparticles. In the current study, Fe_xO_y-NPs were synthesized by two different methods: via green synthesis through the use of polyphenols, which were extracted from Phoenix dactylifera L.; and via chemical synthesis, in which the reducing agent was a chemical (NaOH), and iron chloride was used as a precursor. Thus, polyphenol extraction and its ability to produce nanoparticles were evaluated based on the drying temperature used during the Phoenix dactylifera L. recollection, as well as the extraction solvent used. The results highlight the potential of polyphenols present in Phoenix dactylifera L. for the sustainable manufacture of Fe_xO_y-NPs. Finally, green and chemical syntheses were compared on the basis of physicochemical characteristics and functional properties.

Biologically synthesized iron nanoparticles (FeNPs) from Phoenix dactylifera have anti-bacterial activities

Nanotechnology is a vast field of science with the most vibrant and conspicuous applications. The green synthesis approach is cost-effective, eco-friendly, and produces the most stable metal-based nanoparticles without the use of toxic chemicals. This study presents the green synthesis of iron nanoparticles (FeNPs). For biosynthesis of FeNPs, Phoenix dactylifera extract was used as a reducing agent and iron sulfate heptahydrate (FeSO4·7H2O) was used as a substrate. FeNPs were characterized by different techniques including UV-Visible spectroscopy, Fourier transform infrared spectroscopy (FTIR), and nano zeta-sizer analysis. The antimicrobial activity of FeNPs synthesized by using an aqueous extract of Phoenix dactylifera was evaluated against Escherichia coli, Bacillus subtilis, Micrococcus leutus, and Klebsiella pneumoniae. A notable color change from yellow to black confirmed the synthesis of FeNPs. The sharp peak at 450 nm UV-Visible spectroscopy confirmed the synthesis of FeNPs. FTIR showed the presence of O-H and C=C stretching due to the presence of phenol and alkene functional groups. The average size of FeNPs was 6092 d.nm. The results of antimicrobial activity showed that FeNPs exhibit different potential against different bacterial strains with a maximum 25 ± 0.360 zone of inhibition against Escherichia coli. Thus, green synthesized FeNPs could be used as potential antimicrobial agents.

Advanced treatment of effluent extended aeration process using biological aerated filter (BAF) with natural media: modification in media, design and backwashing process

Biological aerated filters (BAFs) have high filtration efficiency due to their tolerance of hydraulic and organic shocks are suitable for the treatment of complex and sanitary wastewater. In this study, for the first time, natural media of date kernel from Bam city was used as the BAF reactor media, with a meshing sand filter separated by a standard metal grid from the natural filter section used at the end of the reactor. This can be considered an innovation in the media and filtration. Aeration in the related reactor with 160 cm height was performed bilaterally as up-flow and continuously by nozzles throughout the reactor media. In this work, the actual effluent of the hospital wastewater treatment plant was employed as the inflow wastewater to the reactor, and its organic and inorganic parameters were measured before and after the treatment by the BAF reactor. The backwashing process was also studied in three ways: bottom backwashing (TB), top backwashing (BB), and top and bottom backwashing (TBBS), to determine the amount of water consumed and to achieve the desired result. According to the results obtained in this study, the removal efficiencies of inorganic and microbial contaminants, amoxicillin and azithromycin were obtained as follows: BOD₅: 98.48%, COD: 92.42%, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${\text{NO}}_{3}^{ - }$$\end{document}NO3-: 99.4%, P: 93.3%, Coliforms: 97%, Color: 42.8%, Turbidity: 95%, Sulphate: 30%, TSS: 98.9%, Amoxicillin: 20% and azithromycin: 13%. In the backwashing process, the amount of water consumed in these three TB, BB, and TBBS methods were obtained 300, 164, and 118 L, respectively, So, TBBS method was selected as the optimal method. Based on the results obtained in this study, it is concluded that the BAF process with natural date kernel has a high efficiency in removing organic and inorganic contaminants from hospital wastewater, also the concentration of most of the effluent parameters was less or in accordance with EPA standard.

Sono-Biosynthesis and Characterization of AuNPs from Danube Delta Nymphaea alba Root Extracts and Their Biological Properties

Root extracts from Danube Delta Nymphaea alba were used to prepare gold nanoparticles (AuNPRn) by reducing HAuCl4 at different pHs (6.4-8.4) using ultrasonic irradiation: an easy, cheap, eco-friendly and green approach. Their antibacterial and anticancer activities were evaluated against Staphylococcus aureus and Escherichia coli, and A2780 ovarian cancer cells, respectively. The AuNPRn were characterized concerning their phytoconstituents (polyphenols, flavonoids and condensed tannins) and gold content. All of the nanoparticles were negatively charged. AuNPRn exhibited a hydrodynamic size distribution ranging from 32 nm to 280 nm, with the larger nanoparticles being obtained with an Au/root extract ratio of 0.56, pH 7 and 10 min of sonication (AuNPR1), whereas the smallest were obtained with an Au/root extract ratio of 0.24, pH 7.8 and 40 min of sonication (AuNPR4). The TEM/SEM images showed that the AuNPRn had different shapes. The ATR-FTIR indicated that AuNPRn interact mainly with hydroxyl groups present in the polyphenol compounds, which also confirm their high antioxidant capacity, except for AuNPR2 obtained at pH 6.4. Among the AuNPRn, the smallest ones exhibited enhanced antimicrobial and anticancer activities.

Phyto-Engineered Gold Nanoparticles (AuNPs) with Potential Antibacterial, Antioxidant, and Wound Healing Activities Under in vitro and in vivo Conditions

Background

A diabetic ulcer is one of the major causes of illness among diabetic patients that involves severe and intractable complications associated with diabetic wounds. Hence, a suitable wound-healing agent is urgently needed at this juncture. Greener nanotechnology is a very promising and emerging technology currently employed for the development of alternative medicines. Plant-mediated synthesis of metal nanoparticles has been intensively investigated and regarded as an alternative strategy for overcoming various diseases and their secondary complications like microbial infections. Hence, we are interested in developing phyto-engineered gold nanoparticles as useful therapeutic agents for the treatment of infectious diseases and wounds effectively.

Methods and Results

We have synthesized phyto-engineered gold nanoparticles from the aqueous extract of Acalypha indica and characterized using advanced bio-analytical techniques. The surface plasmon resonance feature and crystalline behavior of gold nanoparticles were revealed by ultraviolet-visible spectroscopy and X-ray diffraction, respectively. High-performance liquid chromatography analysis of the extract demonstrated the presence of different constituents, while major functional groups were interpreted by the Fourier-transform infrared spectroscopy as the various stretching vibrations appeared for important O-H (3443 cm⁻¹), C=O (1644 cm⁻¹) and C-O (1395 cm⁻¹) groups. Scanning electron microscopy, high-resolution transmission electron microscopy results revealed a distribution of spherical and rod-like nanostructures with 20 nm of size. The gold nanoparticle-coated cotton fabric was evaluated for the antibacterial activity against Staphylococcus epidermidis and Escherichia coli bacterial strains which revealed remarkable inhibition at the zone of inhibition of 31 mm diameter against S. epidermidis. Further, antioxidant activity was tested for their free radical scavenging property, and the maximum antioxidant activity of the extract containing gold nanoparticles was found to be 80% at 100 µg/mL. The potent free radical scavenging property of the nanoparticles is observed at IC₅₀ value 16.25 µg/mL. Moreover, in vivo wound-healing activity was carried out using BALB/c mice model with infected diabetic wounds and observed the stained microscopic images at different time intervals (day 2, day 7 and day 15). It was noted that in 15 days, the wound area is completely re-epithelialized due to the presence of different morphologies such as spherical, needle and triangle nanoparticles. The re-epithelialization layer is fully covered by nanoparticles on the wound area and also collagen filled in the scar tissue when compared with the control group.

Conclusion

The pharmacological evaluation results of the study indicated an encouraging antibacterial and antioxidant activity of the greener synthesized gold nanoparticles tethered with aqueous extract of Acalypha indica. Moreover, we demonstrated enhanced in vivo wound-healing efficiency of the synthesized gold nanoparticles through the animal model. Thus, the outcome of this work revealed that the phyto-engineered gold nanoparticles could be useful for biomedical applications, especially in the development of promising antibacterial and wound-healing agents.

Recent Developments in the Facile Bio-Synthesis of Gold Nanoparticles (AuNPs) and Their Biomedical Applications

Gold nanoparticles (AuNPs) are extensively studied nanoparticles (NPs) and are known to have profound applications in medicine. There are various methods to synthesize AuNPs which are generally categorized into two main types: chemical and physical synthesis. Continuous efforts have been devoted to search for other more environmental-friendly and economical large-scale methods, such as environmentally friendly biological methods known as green synthesis. Green synthesis is especially important to minimize the harmful chemical and toxic by-products during the conventional synthesis of AuNPs. Green materials such as plants, fungi, microorganisms, enzymes and biopolymers are currently used to synthesize various NPs. Biosynthesized AuNPs are generally safer for use in biomedical applications since they come from natural materials themselves. Multiple surface functionalities of AuNPs allow them to be more robust and flexible when combined with different biological assemblies or modifications for enhanced applications. This review focuses on recent developments of green synthesized AuNPs and discusses their numerous biomedical applications. Sources of green materials with successful examples and other key parameters that determine the functionalities of AuNPs are also discussed in this review.

Simple, green approach for the synthesis of solid support-embedded PdNPs for ligand exchange

Green approaches have the potential to significantly reduce the costs and environmental impact of chemical syntheses. Here, the authors used green tea (GT) leaf extract to synthesise and anchor palladium nanoparticles (PdNPs) to silica. The synthesised PdNPs in GT extract were characterised by ultraviolet-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, and transmission electron microscopy. PdNPs primarily formed as capped NPs dispersed in GT extract before reduction completed after 24 h. This capped phytochemical solution was employed as a green precursor solution to synthesise PdNP-embedded solid supports. The morphology of PdNPs anchored to silica differed to that of PdNPs in solution. Silica-embedded PdNPs was employed as a new ligand exchanger to isolate trace polycyclic aromatic sulphur heterocycles from a hydrocarbon matrix. The isolation efficiency of the new, greener ligand exchanger was the same as an efficient chemical ligand exchanger and may, therefore, hold promise for future applications.

Phyto-Nanocatalysts: Green Synthesis, Characterization, and Applications

Catalysis represents the cornerstone of chemistry, since catalytic processes are ubiquitous in almost all chemical processes developed for obtaining consumer goods. Nanocatalysis represents nowadays an innovative approach to obtain better properties for the catalysts: stable activity, good selectivity, easy to recover, and the possibility to be reused. Over the last few years, for the obtaining of new catalysts, classical methods—based on potential hazardous reagents—have been replaced with new methods emerged by replacing those reagents with plant extracts obtained in different conditions. Due to being diversified in morphology and chemical composition, these materials have different properties and applications, representing a promising area of research. In this context, the present review focuses on the metallic nanocatalysts’ importance, different methods of synthesis with emphasis to the natural compounds used as support, characterization techniques, parameters involved in tailoring the composition, size and shape of nanoparticles and applications in catalysis. This review presents some examples of green nanocatalysts, grouped considering their nature (mono- and bi-metallic nanoparticles, metallic oxides, sulfides, chlorides, and other complex catalysts).

Ficus retusa-stabilized gold and silver nanoparticles: Controlled synthesis, spectroscopic characterization, and sensing properties

Ficus retusa was used as reducing and stabilizing agent in the green synthesis of silver and gold nanoparticles with high dispersion stability and controllable size and shape. The controlling of reaction conditions i.e. contact time, extract quantity, metal concentration, and pH value enables the tuning of the particle size and size distribution of the metal nanoparticles. UV-visible spectroscopy was used to follow the spectral profile changes of the surface plasmon resonance of the metal nanoparticles due to different treatments. The surface plasmon resonance varies between 400 and 432 nm and between 522 and 554 nm for silver and gold nanoparticles, respectively, depending on the different reaction parameters. Atomic force and transmission electron microscopy results confirmed the success of preparation of spherical silver (15 nm) and gold (10-25 nm) nanoparticles with narrow size-distribution. Fourier transform infrared spectroscopy suggested the phenolic compounds play the key role in the reduction and stabilizing of metal ions. The colorimetric sensitivity of silver and gold nanoparticles to detect the presence of heavy metals in water was studied.

From biotechnology principles to functional and low-cost metallic bionanocatalysts

Chemical, physical and mechanical methods of nanomaterial preparation are still regarded as mainstream methods, and the scientific community continues to search for new ways of nanomaterial preparation. The major objective of this review is to highlight the advantages of using green chemistry and bionanotechnology in the preparation of functional low-cost catalysts. Bionanotechnology employs biological principles and processes connected with bio-phase participation in both design and development of nano-structures and nano-materials, and the biosynthesis of metallic nanoparticles is becoming even more popular due to; (i) economic and ecologic effectiveness, (ii) simple one-step nanoparticle formation, stabilisation and biomass support and (iii) the possibility of bio-waste valorisation. Although it is quite difficult to determine the precise mechanisms in particular biosynthesis and research is performed with some risk in all trial and error experiments, there is also the incentive of understanding the exact mechanisms involved. This enables further optimisation of bionanoparticle preparation and increases their application potential. Moreover, it is very important in bionanotechnological procedures to ensure repeatability of the methods related to the recognised reaction mechanisms. This review, therefore, summarises the current state of nanoparticle biosynthesis. It then demonstrates the application of biosynthesised metallic nanoparticles in heterogeneous catalysis by identifying the many examples where bionanocatalysts have been successfully applied in model reactions. These describe the degradation of organic dyes, the reduction of aromatic nitro compounds, dehalogenation of chlorinated aromatic compounds, reduction of Cr(VI) and the synthesis of important commercial chemicals. To ensure sustainability, it is important to focus on nanomaterials that are capable of maintaining the important green chemistry principles directly from design inception to ultimate application.

Gold and Silver Nanoparticles Biomimetically Synthesized Using Date Palm Pollen Extract-Induce Apoptosis and Regulate p53 and Bcl-2 Expression in Human Breast Adenocarcinoma Cells

Recently, several attempts have been made to use the phytopharmaceuticals from plant extracts as reducing, capping and stabilizing agents for the biomimetic synthesis of various metal nanoparticles conjugated to the phytopharmaceuticals. These biogenic metal nanoparticles are non-toxic and can be used as contrast agents, drug delivery vehicles and photothermal agents for cancer therapy. Herein, we report the synthesis of both silver and gold nanoparticles using the pollen extract of Phoenix dactylifera (Date Palm), characterization using UV-visible spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy, quantitation of phytochemicals capping the nanoparticles using Folin - Ciocalteu's method, cytotoxicity studies on MCF-7 breast cancer cells, cancer cell death analysis using fluorescent microscopy, and modulation of expression of the pro-apoptotic p53 and anti-apoptotic Bcl-2 proteins. The biosynthesis resulted in stable and poly-dispersed silver nanoparticles and gold nanoparticles, exhibiting strong and broad surface plasmon absorption peaks. The elemental analysis confirmed the presence of gold and silver of high purity and also the organic moieties from the plant extract acting as capping and stabilizing agents. The biogenic nanoparticles also exhibited dose-dependent cytotoxicity on MCF-7 cells and showed signs of apoptotic cell death. Immunoassays revealed the upregulation of the pro-apoptotic protein p53 and down-regulation of the anti-apoptotic protein Bcl-2 after the nanoparticle treatment.

Secondary Metabolites in the Green Synthesis of Metallic Nanoparticles

The ability of organisms and organic compounds to reduce metal ions and stabilize them into nanoparticles (NPs) forms the basis of green synthesis. To date, synthesis of NPs from various metal ions using a diverse array of plant extracts has been reported. However, a clear understanding of the mechanism of green synthesis of NPs is lacking. Although most studies have neglected to analyze the green-synthesized NPs (GNPs) for the presence of compounds derived from the extract, several studies have demonstrated the conjugation of sugars, secondary metabolites, and proteins in these biogenic NPs. Despite several reports on the bioactivities (antimicrobial, antioxidant, cytotoxic, catalytic, etc.) of GNPs, only a handful of studies have compared these activities with their chemically synthesized counterparts. These comparisons have demonstrated that GNPs possess better bioactivities than NPs synthesized by other methods, which might be attributed to the presence of plant-derived compounds in these NPs. The ability of NPs to bind with organic compounds to form a stable complex has huge potential in the harvesting of precious molecules and for drug discovery, if harnessed meticulously. A thorough understanding of the mechanisms of green synthesis and high-throughput screening of stabilizing/capping agents on the physico-chemical properties of GNPs is warranted to realize the full potential of green nanotechnology.

Green synthesis of gold nanoparticles using a cheap Sphaeranthus indicus extract: Impact on plant cells and the aquatic crustacean Artemia nauplii

The impact of green-fabricated gold nanoparticles on plant cells and non-target aquatic species is scarcely studied. In this research, we reported an environment friendly technique for the synthesis of gold nanoparticles (Au NPs) using the Sphaeranthus indicus leaf extract. The formation of the metal NPs was characterized by UV-Visible and FT-IR spectroscopy, XRD, SEM and TEM analyses. The UV-Visible spectra of Au NPs showed a surface plasmon resonance peak at 531nm. FT-IR analysis indicated functional bio-molecules associated with Au NPs formation. The crystalline nature of Au nanoparticles was confirmed by their XRD diffraction pattern. TEM revealed the spherical shape with a mean particle size of 25nm. Au NPs was tested at 0, 1, 3, 5, 7 and 10% doses in mitotic cell division assays, pollen germination experiments, and in vivo toxicity trials against the aquatic crustacean Artemia nauplii. Au NPs did not show any toxic effects on plant cells and aquatic invertebrates. Notably, Au NPs promoted mitotic cell division in Allium cepa root tip cells and germination of Gloriosa superba pollen grains. Au NPs showed no mortality on A. nauplii, all the tested animals showed 100% survivability. Therefore, these Au NPs have potential applications in the development of pollen germination media and plant tissue culture.

Phyto-assisted synthesis, characterization and applications of gold nanoparticles - A review

Nanotechnology is the formation, running and use of operation at the nanomaterial size scale (1-100 nm). Nanoscale materials can also be obtained by biological synthesis materials via eco-friendly green chemistry based technique. Current development and numerous strategies involved in the green synthesis of nanoparticles were focussed. This review mainly focused on plants which include scientific name, family name, common name, plant parts, its characterization, size and shape of the nanoparticles. Plant extract which was done experimentally gives its various characterization which leads to the identification of compounds of different nano size and shape. Biosynthesis of gold nanoparticles is in different shapes like spherical, rod, cubic, triangle and also in different sizes. Various application and importance of gold nanoparticles in numerous fields were discussed. The mark of the review is to provide an overview of recent learning in biosynthesized nanoparticles, its characterization and their potential applications.

Green Synthesis and Catalytic Activity of Gold Nanoparticles Synthesized by Artemisia capillaris Water Extract

Gold nanoparticles were synthesized using a water extract of Artemisia capillaris (AC-AuNPs) under different extract concentrations, and their catalytic activity was evaluated in a 4-nitrophenol reduction reaction in the presence of sodium borohydride. The AC-AuNPs showed violet or wine colors with characteristic surface plasmon resonance bands at 534~543 nm that were dependent on the extract concentration. Spherical nanoparticles with an average size of 16.88 ± 5.47~29.93 ± 9.80 nm were observed by transmission electron microscopy. A blue shift in the maximum surface plasmon resonance was observed with increasing extract concentration. The face-centered cubic structure of AC-AuNPs was confirmed by high-resolution X-ray diffraction analysis. Based on phytochemical screening and Fourier transform infrared spectra, flavonoids, phenolic compounds, and amino acids present in the extract contributed to the reduction of Au ions to AC-AuNPs. The average size of the AC-AuNPs decreased as the extract concentration during the synthesis was increased. Higher 4-nitrophenol reduction reaction rate constants were observed for smaller sizes. The extract in the AC-AuNPs was removed by centrifugation to investigate the effect of the extract in the reduction reaction. Interestingly, the removal of extracts greatly enhanced their catalytic activity by up to 50.4 %. The proposed experimental method, which uses simple centrifugation, can be applied to other metallic nanoparticles that are green synthesized with plant extracts to enhance their catalytic activity.

Whole resting cells vs. cell free extracts of Candida parapsilosis ATCC 7330 for the synthesis of gold nanoparticles

The cell free extracts of Candida parapsilosis ATCC 7330 are more efficient than the whole resting cells of the yeast in the synthesis of directly usable gold nanoparticles as revealed by this systematic study. Cell free extracts yielded gold nanoparticles of hydrodynamic diameter (50-200 nm). In this study, the total protein concentration influences the nanofabrication and not only the reductase enzymes as originally thought. Powder X-ray diffraction studies confirm the crystalline nature of the gold nanoparticles. Fourier Transform Infra Red spectroscopy and thermal gravimetric analysis suggests that the biosynthesized gold nanoparticles are capped by peptides/proteins. Dispersion experiments indicate a stable dispersion of gold nanoparticles in pH 12 solutions which is also confirmed by electron microscopic analysis and validated using a surface plasmon resonance assay. The effectiveness of the dispersed nanoparticles for the reduction of 4-nitrophenol using sodium borohydride as a reductant further confirms the formation of functional gold nanoparticles. It is also reported that gold nanoparticles with mean particle diameter of 27 nm are biosynthesized inside the whole cell by transmission electron microscopy analysis. With optimized reaction conditions, maximum gold bioaccumulation with the 24 h culture age of the yeast with cellular uptake of ~1010 gold atoms at the single cell level is achieved but it is not easy to extract the gold nanoparticles from the whole resting cells.

Phyto-synthesis and structural characterization of catalytically active gold nanoparticles biosynthesized using Delonix regia leaf extract

Biological methods of nanoparticles synthesis are ecologically sound and sustainable alternative to the conventional methods. On the basis of aforesaid premise, the present study deals with the optimization and fabrication of gold nanoparticles (Au-NPs) using easily available bio-resource, Delonix regia leaf extract. The use of practically nontoxic natural extracts and water allows the synthesis pathways presented to be considered as ‘‘green’’ and so permitting the synthesized Au-NPs to be used in sensitive areas, such as bioremediation. Various characterization techniques are adopted for the evaluation of size, stability, morphology, crystal nature, and purity of nanoparticles. Ultraviolet–visible spectroscopy analysis showed a surface Plasmon resonance peak for prepared Au-NPs at 542 nm, and its absorbance increased with increasing the interaction time. Transmission electron microscopy analysis showed that the particles were spherical and 4–24 nm in size. Energy dispersive X-ray spectroscopy analysis displayed a 2.2 keV peak corresponding to the pure phase gold nanocrystal. X-ray diffraction analysis proved the fabrication of crystalline Au-NPs with face-centered cubic geometry within 10 min. Furthermore, ζ potential (−15 mV) and Fourier transform infrared data suggested the role of polar polyphenolic compounds of leaf extract in fabrication and stabilization process. Biofabricated nanoparticles are demonstrated to have catalytic activity for the reduction of toxic nitro-organic pollutant o-nitroaniline. Therefore, the present study offers a straightforward, cost-efficient, eco-friendly, and sustainable alternative for the fabrication of catalytically active Au-NPs.

Biosynthesis of gold nanoparticles: A green approach

Nanotechnology is an immensely developing field due to its extensive range of applications in different areas of technology and science. Different types of methods are employed for synthesis of nanoparticles due to their wide applications. The conventional chemical methods have certain limitations with them either in the form of chemical contaminations during their syntheses procedures or in later applications and use of higher energy. During the last decade research have been focussed on developing simple, clean, non-toxic, cost effective and eco-friendly protocols for synthesis of nanoparticles. In order to get this objective, biosynthesis methods have been developed in order to fill this gap. The biosynthesis of nanoparticles is simple, single step, eco-friendly and a green approach. The biochemical processes in biological agents reduce the dissolved metal ions into nano metals. The various biological agents like plant tissues, fungi, bacteria, etc. are used for biosynthesis for metal nanoparticles. In this review article, we summarised recent literature on biosynthesis of gold nanoparticles which have revolutionised technique of synthesis for their applications in different fields. Due to biocompatibility of gold nanoparticles, it has find its applications in biomedical applications. The protocol and mechanism of biosynthesis of gold nanoparticles along with various applications have also been discussed.

Multipurpose effectiveness of Couroupita guianensis-synthesized gold nanoparticles: high antiplasmodial potential, field efficacy against malaria vectors and synergy with Aplocheilus lineatus predators

Mosquito-borne diseases represent a deadly threat for millions of people worldwide. According to recent estimates, about 3.2 billion people, almost half of the world's population, are at risk of malaria. Malaria control is particularly challenging due to a growing number of chloroquine-resistant Plasmodium and pesticide-resistant Anopheles vectors. Newer and safer control tools are required. In this research, gold nanoparticles (AuNPs) were biosynthesized using a cheap flower extract of Couroupita guianensis as reducing and stabilizing agent. The biofabrication of AuNP was confirmed by UV-vis spectrophotometry, Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray diffraction (XRD), zeta potential, and particle size analysis. AuNP showed different shapes including spheres, ovals, and triangles. AuNPs were crystalline in nature with face-centered cubic geometry; mean size was 29.2-43.8 nm. In laboratory conditions, AuNPs were toxic against Anopheles stephensi larvae, pupae, and adults. LC50 was 17.36 ppm (larva I), 19.79 ppm (larva II), 21.69 ppm (larva III), 24.57 ppm (larva IV), 28.78 ppm (pupa), and 11.23 ppm (adult). In the field, a single treatment with C. guianensis flower extract and AuNP (10 × LC50) led to complete larval mortality after 72 h. In standard laboratory conditions, the predation efficiency of golden wonder killifish, Aplocheilus lineatus, against A. stephensi IV instar larvae was 56.38 %, while in an aquatic environment treated with sub-lethal doses of the flower extract or AuNP, predation efficiency was boosted to 83.98 and 98.04 %, respectively. Lastly, the antiplasmodial activity of C. guianensis flower extract and AuNP was evaluated against CQ-resistant (CQ-r) and CQ-sensitive (CQ-s) strains of Plasmodium falciparum. IC50 of C. guianensis flower extract was 43.21 μg/ml (CQ-s) and 51.16 μg/ml (CQ-r). AuNP IC50 was 69.47 μg/ml (CQ-s) and 76.33 μg/ml (CQ-r). Overall, our results showed the multipurpose effectiveness of C. guianensis-synthesized AuNPs, since they may be proposed as newer and safer tools in the fight against CQ-r strains of P. falciparum and for field control of malaria vectors, in synergy with wonder killifish predators.

Biogenic synthesis of metallic nanoparticles and prospects toward green chemistry

The immense importance of nanoparticles and their applications is a strong motivation for exploring new synthetic techniques. However, due to strict regulations that manage the potential environmental impacts greener alternatives for conventional synthesis are the focus of intense research. In the scope of this perspective, a concise discussion about the use of green reducing and stabilizing agents toward the preparation of metal nanoparticles is presented. Reports on the synthesis of noble metal nanoparticles using plant extracts, ascorbic acid and sodium citrate as green reagents are summarized and discussed, pointing toward an urgent need of understanding the mechanistic aspects of the involved reactions.

Controllable biosynthesis of gold nanoparticles from a Eucommia ulmoides bark aqueous extract

The present work reports the green synthesis of gold nanoparticles (AuNPs) by water extract of Eucommia ulmoides (E. ulmoides) bark. The effects of various parameters such as the concentration of reactants, pH of the reaction mixture, temperature and the time of incubation were explored to the controlled formation of gold nanoparticles. The characterization through high resolution-transmission electron microscopic (HRTEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) infer that the as-synthesized AuNPs were spherical in shape with a face cubic crystal (FCC) structure. The results from zeta potential and dynamic light scattering (DLS) suggest the good stability and narrow size distribution of the AuNPs. This method for synthesis of AuNPs is simple, economic, nontoxic and efficient. The as-synthesized AuNPs show excellent catalytic activity for the catalytic reducing decoloration of model compounds of azo-dye: reactive yellow 179 and Congo red.