Polysaccharides and phytochemicals: a natural reservoir for the green synthesis of gold and silver nanoparticles

Currently, sustainability initiatives that use green chemistry to improve and/or protect our global environment are becoming focal issues in many fields of research. Instead of using toxic chemicals for the reduction and stabilisation of metallic nanoparticles, the use of various biological entities has received considerable attention in the field of nanobiotechnology. Among the many possible natural products, polysaccharides and biologically active plant products represent excellent scaffolds for this purpose. Polysaccharides have hydroxyl groups, a hemiacetal reducing end, and other functionalities that can play important roles in both the reduction and the stabilisation of metallic nanoparticles. Among the various categories of compounds in plants that have potent biological activities, phytochemicals are emerging as an important natural resource for the synthesis of metallic nanoparticles. The focus of this review is the application of polysaccharides and phytochemicals in the green synthesis of gold and silver nanoparticles to afford biocomposites with novel uses in nanomedicine and as nanocomposites.     

Biogenic materialization using pear extract intended for the synthesis and design of ordered gold nanostructures

We report a facile, green, and biomimetic reduction route coupled with the synthesis and biomolecular-based well-defined self-assembly of gold nanoparticles (AuNPs), without using any organic solvents or any toxic reducing or capping agents. To demonstrate the potential use of pear phytochemicals for the materialization of AuNPs, we propose that the available biomolecules appending on the AuNPs surface and subsequently observed their importance in assembly designs. The spatial array of AuNPs was investigated precisely by using a high-resolution transmission electron microscopy. This method offered biomolecular capping of the AuNPs during and after synthesis and thus provides a promising alternative for nanosurface engineering. The peptide and other biomolecule-based coatings on the AuNPs are applicable for their stability and healthy capping. The hybrid “biomolecular-inorganic” system will be suitable for safe application in medical and diagnostic fields.     

The effect of arginine on gold nanoparticles in colloidal solutions and in thin films

Gold nanoparticles were prepared in aqueous colloidal solutions and their interaction with L-arginine solutions at different concentrations was investigated by UV-vis spectroscopy, transmission electron microscopy (TEM) and atomic force microscopy (AFM). The shift towards red of the absorption maximum of gold nanoparticles with increasing L-arginine concentration and in time, and the apparition of a new large band at higher wavelength evidence the formation of assemblies of gold nanoparticles, mediated by the amino acid. TEM images present the progress in the building process of supermolecular structures. Further, the AFM images show the self assemblies of gold nanoparticles capped with L-arginine well ordered in large domains on silanized glass. As a model for the process, we suggest that the positively charged guanidinium group of L-arginine is anchored on the negative citrate capped gold nanoparticles, while the other two functionalities of L-arginine are involved in the bonding between gold nanoparticles. The ability of arginine to specifically bind gold nanoparticles could lead to an increased ability of proteins, containing arginine, to specifically bind to nanogold. Then, they bind other target proteins or different ligands underlying numerous biological and medical applications that range from nanoscale biosensors, cell-cell communications to targeted delivery of drugs to cancer cells.     

Green synthesis of gold nanoparticles using ethanolic leaf extract of Centella asiatica

Here, we report a novel use of the ethanolic leaf extract of Centella asiatica to produce gold nanoparticles by reduction of AuCl₄⁻ ions. The phytochemicals present in the leaf extract served as effective reducing and capping agent. The gold nanoparticles obtained were characterized by UV-visible spectra, transmission electron microscopy (TEM) and X-ray diffraction (XRD). TEM studies showed the particles to be of various shapes and sizes. Selected-area electron diffraction (SAED) pattern and high-resolution TEM image confirmed a fcc phase and high crystallinity of the particles. The XRD patterns showed a (1 1 1) preferential orientation of the gold nanoparticles. Fourier transform infra-red spectroscopy (FTIR) measurements showed the GNPs having a coating of phenolic compounds indicating a possible role of biomolecules responsible for capping and efficient stabilization of the gold nanoparticles. As no synthetic reagents were used in this method, the synthesized gold nanoparticles have potential for application in bio-molecular imaging and therapy.     

β-glucosidase assisted biosynthesis of gold nanoparticles: A green chemistry approach

Biogenic gold nanoparticles using medically important phytochemical (β-glucosidase) are demonstrated herein. The reduction capabilities of phytochemical and their ability to stabilize the new genre gold nanoparticles, were characterized using UV-visible, FT-IR, HR-TEM and XRD measurements. This report also focuses the newly formed gold nanoparticles application on promoting the defensive mechanism of silkworm Bombyx mori. The results highlight the possibility of green pathways to produce functionalized gold nanoparticles of medicinal significance.     

Biosynthesis of controllable size and shape gold nanoparticles by black seed (Nigella sativa) extract

We report on the use of black seed (Nigella sativa) extract, previously not exploited, in synthesis of gold nanoparticles. On treating aqueous chloroauric acid solution with black seed extract, the antioxidant activities critical roles of the various phytochemicals is observed leading to the formation of crystalline and poly shaped gold nanoparticles. In this research work, we developed a rapid and non-toxic method for the preparation of biocompatible gold nanoparticles by two different synthetic routes: microwave irradiation and thermo-induced procedures. The nanoparticles were characterized and investigated by ultraviolet-visible (UV-Vis) spectrophotometry, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD).The size and shape of the nanoparticles were found to be very sensitive to the quantity of the extract. As the amount of extract is increased, the stronger the interaction between the extract biomolecules and nascent nanoparticles, thus the yield of nanoparticles increased as shown by surface plasmon resonance bands in the UV-vis-NIR spectra. The reaction temperature has a significant role in production of gold nanoparticles with different shapes. The XRD studies reflect an interesting feature indicates that gold nanocrystals are highly anisotropic in nature, mainly triangular and hexagonal shapes, and that the particles are (111) oriented. The observed characteristics suggest the application of the biocompatible gold nanoparticles to future in vivo imaging and therapy.     

Green synthesis and characterisation of antioxidant-tagged gold nanoparticle (X-GNP) and studies on its potent antimicrobial activity

Alternanthera philoxeroides (Mart.), a weed, mainly from tropical origin and easily available worldwide. People used to eat it as a food mainly in South Africa. In our previous report we have thoroughly characterise several important phenolics, monoterpene and phenylpropane from methanol soluble fraction of Alternenthera leaves (fraction X) and also reported their α-glucosidase inhibitory, antimicrobial and antioxidant activities. All these isolated natural compounds are well characterised and widely studied. In our present study we try to use this beneficial fraction (named fraction X) in green synthesis of gold nanoparticles (X-GNP). We also try to explore the beneficial aspects of green synthesis in comparison with commonly used chemical synthesis method (GNP) in context with their antimicrobial activity. UV/Vis spectroscopy, DLS, Zeta potential, FT-IR, EDAX and other microscopic techniques namely: SEM, AFM were used to characterise the synthesised nanoparticles. Different important microbial strains were used to evaluate the antimicrobial activity of prepared nanoparticles. Overall the studies suggest successful synthesis of green nanoparticles (X-GNP) and also showed the improvement in antimicrobial activity of X-GNP nanoparticles.     

Chemical solution approaches to YBa2Cu3O7_delta-Au nanocomposite superconducting thin films

We explore the feasibility of preparing YBa2CU3O7-Au (YBCO-Au) nanocomposite thin films by chemical solution deposition (CSD). Two approaches were used: (i) A standard in-situ methodology where Au metallorganic salts are added into the precursor solution of YBCO trifluoroacetate (TFA) salts and (ii) a novel approach where stable colloidal solutions of preformed gold nanoparticles (5-15 nm) were homogeneously mixed with TFA-YBCO solutions. A detailed analysis of the microstructure of the films showed that in both cases, there is a strong tendency of gold nanoparticles to migrate to the film surface. However the kinetics of this migration evidences important differences and in the case of preformed nanoparticles their size remains unchanged (a few nanometers) whereas for the in-situ nanocomposites gold ripening leads to large particles (hundreds of nanometers). The grown YBCO-Au films showed good superconducting characteristics (J(c) 2 MA/cm2 at 77 K) but the absence of Au inclusions inside the YBCO matrix explains the fact that no enhancement of vortex pinning was observed.     

Flower-shaped gold nanoparticles: synthesis, characterization and their application as SERS-active tags inside living cells

The detection of Raman signals inside living cells is a topic of great interest in the study of cell biology mechanisms and for diagnostic and therapeutic applications. This work presents the synthesis and characterization of flower-shaped gold nanoparticles and demonstrates their applicability as SERS-active tags for cellular spectral detection. The particles were synthesized by a facile, rapid new route that uses ascorbic acid as a reducing agent of gold salt. Two triarylmethane dyes which are widely used as biological stains, namely malachite green oxalate and basic fuchsin, were used as Raman-active molecules and the polymer mPEG-SH as capping material. The as-prepared SERS-active nanoparticles were tested on a human retinal pigment epithelial cell line and found to present a low level of cytotoxicity and high chemical stability together with SERS sensitivity down to picomolar particle concentrations.     

Green synthesis of gold nanoparticles: Its effect on cocoon and silk traits of mulberry silkworm (Bombyx mori L.)

In the present century the small particles are unique phenomenon which can be developed by bottom-up and top-down processes. These small particles may be considered as nanoparticles which help to build up a technology called nanotechnology. Nanomaterials are those materials which possess the length scales below 100 nm and quite often they make a comparison with a human hair, which is about 80,000 nm wide. We have introduced this technology, specially the green synthesis of gold (Au) nanoparticles in silkworm (Bombyx mori L.). The gold nanoparticles clearly indicate that they have a tremendous effect on enhancement of silk proteins and thus the enhancement of the cocoon weight in silkworms. Gold nanoparticles were prepared from onion, Allium cepa L. The extracted green gold nanomaterials from A. cepa were confirmed by UV-Vis spectrophotometer, XRD, FTIR, SEM, TEM and AFM. The function of green gold nanomaterials extracted from A. cepa was tested on silkworm physiology. We have used UV for judgment of the nature of particles and spectrum peak wavelength showed an absorption peak at 535 nm and indicated the wavelength of the surface plasmon resonance in gold nanoparticles (Au NPs). In blank solutions no such absorption peak was observed at 535 nm. Moreover, the gold (Au) XRD spectrum is supposed to and does demonstrate (111), (200), (220), and (311) peaks in the assortment of superimpose on the background. The process includes the (002) trace graphite peaks, where the (111) peak appears to be exceptionally sharp and strong which helps to propose that it is gold in nature. The FTIR shows that the examined particles are gold in nature. In SEM where electrons interact with atoms in the sample, producing various signals that can be detected and that hold information about the sample's surface topography and composition. The electron beam in SEM is generally scanned in a raster scan pattern, and therefore the beam's position is combined and detects the signal to produce an image. SEM can attain a resolution better than 1 nanometer size. The transmission electron microscope helps to accelerate the electrons as a source of elucidation. The AFM measurement is made in three dimensions process and thus it may be measured as horizontal to X-Y plane. Therefore, decree (magnification) measured at Z–direction, which is normally higher than X-Y. The said repulsive force is major one in AFM. Thus the tip and sample may considered to be the specific force in AFM which may measured at Z–direction. The effect of green gold nanoparticles on mulberry silkworm (Bombyx mori L) can exaggerated the silkworm physiological function. Larvae at 50, 100, 200, and 300 ppm doses were studied right from 1st stage to 5th instar stage. Gold nano treatment resulted in significant alterations in the percentage of fibroin and sericin proteins in the 5th instar as compared to that of control. At a 300 ppm dose of green nano gold the percentage of fibroin was 78.07, while sericin decreased from 39.46 (control) to 21.92. It was observed that the green gold nanomaterials have the ability to not only alter the fibroin protein but also enhance the cocoon and silk traits. The aim of this study was to investigate the effect of extra foliation of mulberry leaves with G-GNPs extracted from A. cepa on larval duration, mature silk gland weight, pupal weight, cocoon weight, cocoon shell weight, fibroin and sericins contents, etc. Moreover, the enhanced production of fibroin will explore a new venture in bioengineering and also in biomedical field.     

Shape dependence of nonlinear optical behaviors of gold nanoparticles

Tetrahedral, icosahedral, and cubic gold nanoparticles have been synthesized in experiment by reducing chloroauric acid with ethylene glycol (EG) in the presence of poly(vinylpyrrolidone) (PVP). The nonlinear properties of the gold nanoparticles have been investigated by using the Open-aperture Z-scan technique with the nanosecond pulse at a wavelength of 532 nm. It shows out that all the gold nanoparticles possess strong optical nonlinearities when being excited at their surface plasmon resonances. It is identified that the nonlinear properties of the gold nanoparticles are dependent on their shapes, and the icosahedra gold nanoparticles show much better nonlinear optical properties than the tetrahedral and cubic ones. Moreover, the mechanism for the process of the nonlinear properties is also analyzed.     

Effect of pH on the extra cellular synthesis of gold and silver nanoparticles by Saccharomyces cerevisae

In the present study, the synthesis of gold and silver nanoparticles was investigated using the culture supernatant broth of the yeast Saccharomyces cerevisae. Gold nanoparticles were formed within 24 hours of gold ion coming in contact with the culture supernatant broth. In case of silver the reduction process took 48 hours. The synthesized nanoparticles were investigated by UV-Visible spectroscopy. Distinct surface plasmon peaks were observed at 540 nm and 415 nm for gold and silver nanoparticles respectively. Bio-TEM micrographs of the synthesized nanoparticles indicated that the particles were well dispersed and near spherical in shape. The size range of the gold and silver nanoparticles was around 20-100 nm and 5-20 nm respectively. XRD patterns showed the presence of three distinct peaks corresponding to gold and silver nanoparticles respectively. A pH range of 4 to 6 and 8 to 10 favored optimum synthesis of gold and silver nanoparticles respectively. The process of reduction being extra cellular could be used in future for downstream processing in an eco friendly manner.     

Gold nanoparticles: a revival in precious metal administration to patients

Gold has been used as a therapeutic agent to treat a wide variety of rheumatic diseases including psoriatic arthritis, juvenile arthritis, and discoid lupus erythematosus. Although the use of gold has been largely superseded by newer drugs, gold nanoparticles are being used effectively in laboratory based clinical diagnostic methods while concurrently showing great promise in vivo either as a diagnostic imaging agent or a therapeutic agent. For these reasons, gold nanoparticles are therefore well placed to enter mainstream clinical practice in the near future. Hence, the present review summarizes the chemistry, pharmacokinetics, biodistribution, metabolism, and toxicity of bulk gold in humans based on decades of clinical observation and experiments in which gold was used to treat patients with rheumatoid arthritis. The beneficial attributes of gold nanoparticles, such as their ease of synthesis, functionalization, and shape control are also highlighted demonstrating why gold nanoparticles are an attractive target for further development and optimization. The importance of controlling the size and shape of gold nanoparticles to minimize any potential toxic side effects is also discussed.     

Facile synthesis of gold nanoflowers with high surface-enhanced Raman scattering activity

Highly branched gold nanoflowers are synthesized in high yield by a simple amino-reducing method, without additional seeds or surfactant agents. We present a systematic investigation of the influence of different parameters on the size, morphology, and monodispersity of gold nanoflowers. The initial concentration of reducing agent, the solvent viscosity, and the reaction temperature play critical roles in the formation of nanoparticles. A lower concentration of reducing agent causes larger particles with sharp and dendritic tips. Moreover, with increasing solvent viscosity, the obtained particles have more and larger tips. Examination of the nanoparticles at different reaction stages with transmission electron microscopy and UV-vis spectroscopy reveals the formation of the gold nanoflowers as a classical growth process in which diffusion-controlled growth gives rise to the highly branched structures. Additionally, these gold nanoflowers have prospects for surface-enhanced Raman scattering (SERS) imaging because of their strong SERS enhancement and clean surface.     

Optically understanding the dependence of catalysis kinetics on work function of nanocatalyst

In this work, biogenic ZnO and CuO nanoparticles were fabricated by adopting a complete green aqueous approach utilizing Centella asiatica plant extract. The phytochemicals involved in tailoring the nanoscopic metal oxide particles were characterized vividly. Both of the as-synthesized metal oxide particles are spherical and have a narrow size distribution with an average diameter of about 7 nm as measured via HRTEM. Interestingly, X-ray diffraction (XRD) pattern of ZnO nanoparticles displays the exposure of its (100) hexagonal facet. The ensuing ZnO and CuO nanoscale particles briskly enhanced the reduction of methylene blue, which was otherwise very slow. The reaction follows first-order kinetics and the rate constants follow the order k _uncat < k _{ZnO NPs} < k _{CuO NPs}. The higher catalytic performance of copper oxide nanoparticles than zinc oxide nanoparticles is succinctly established on the basis of their difference in work function values optically.

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Graphical Abstract Co-relating workfunction of green synthesized metal oxide nanocatalysts to reaction kinetics.

     

Phytochemicals-mediated green synthesis of gold nanoparticles using Pterocarpus santalinus L. (Red Sanders) bark extract and their antimicrobial properties

In the present study, phytochemicals-mediated rapid, stable and eco-friendly synthesis of gold nanoparticles (GNPs) using Pterocarpus santalinus L. (Red Sanders) bark extract is reported. The powerful characteristics of different phytochemicals present in P. santalinus L. bark prompted us to determine their efficacy in the bio-reduction of gold chloride trihydrate to the corresponding GNPs. The biosynthesis of GNPs was investigated at the physiological condition (pH?=?7.4). The synthesized GNPs were characterized by UV–visible spectroscopy by measuring the peak in the range of 400–700?nm. The GNPs synthesized at physiological conditions revealed surface plasmon resonance (SPR) at 545?nm. The crystalline nature of GNPs was confirmed by using x-ray diffraction (XRD), and the functional groups adhered on the surface of the GNPs were analyzed by Fourier Transform Infrared spectroscopy (FTIR). Transmission Electron Microscopy (TEM) analysis showed spherical GNPs in the size range of 13–26?nm. The synthesized GNPs exhibited antibacterial activity against Gram-positive and Gram-negative bacterial strains.     

Biosynthesis of bimetallic and core–shell nanoparticles: their biomedical applications – a review

Recently, researchers succeeded in designing and manufacturing a new class of nanoparticles (NPs) called hybrid NPs. Among hybrid NPs, bimetallic and core–shell NPs were a revolutionary step in NPs science. A large number of green physiochemical and methods for nanostructures synthesis have been published. Eventually, physiochemical methods are either expensive or require the use of chemical compounds for the synthesis of bimetallic and core–shell nanostructures. The main challenges that scientists are facing are making the process cheaper, facile and eco‐friendly efficient synthesis process. Green synthesis (biosynthesis) refers to the use of bio‐resources (such as bacteria, fungi, plants or their derivatives) for the synthesis of nanostructures. The popularity of the green synthesis of nanostructures is due to their environmental friendliness and no usage of toxic materials, environmental friendliness for the synthesis or stability of nanostructure. Bimetallic and core–shell NPs have many biomedical applications such as removing heavy metals, parasitology, molecular and microbial sensor, gene carrier, single bacterial detection, oligonucleotide detection and so on. The purpose of this study is to discuss briefly the biosynthesised bimetallic and core–shell NPs, their biomedical applications.Inspec keywords: nanofabrication, nanoparticles, biosensors, microorganisms, molecular biophysics, nanobiotechnologyOther keywords: biosynthesised bimetallic –shell, environmental friendliness, green synthesis, eco‐friendly efficient synthesis process, core–shell nanostructures, bimetallic –shell nanostructures, physiochemical methods, nanostructures synthesis, green physiochemical, NPs science, hybrid NPs, biomedical applications, core–shell nanoparticles, bimetallic –shell nanoparticles, biosynthesis     

Synthesis of 16-Mercaptohexadecanoic acid capped gold nanoparticles and their immobilization on a substrate

Controlled assembly of nanoparticles on substrates is a promising path to develop miniaturized electronic and optical devices. Among the important issues to be addressed in this area include immobilization of the nanoparticles on substrates in order to ensure that the system is robust. In this work, 16-mercaptohexadecanoic acid (16-MHDA) capped gold nanoparticles with a narrow size distribution have been synthesized through a single phase synthesis method and subsequently immobilized on to silicon surface through covalent molecular assembly. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) confirmed the absence of unreacted thiol in the synthesized gold nanoparticles. Presence of gold nanoparticles on Si surface after the immobilization process was confirmed through XPS. Cross-sectional high resolution transmission electron microscopy (HR-TEM) images provide direct evidence that the particles are indeed anchored to the silicon surface. The formation of uniform-sized and separated acid functionalized gold nanoparticles and their immobilization on to Si provide a basis for further nano-structuring.     

Doping and alloying in atomically precise gold nanoparticles

The recent success in the synthesis and total structure determination of atomically precise gold nanoparticles has provided exciting opportunities for fundamental studies as well as the development of new applications. These unique nanoparticles are of molecular purity and possess well defined formulas （i.e., specific numbers of metal atoms and ligands）, resembling organic compounds. Crystallization of such molecularly pure nanoparticles into macroscopic single crystals allows for the determination of total structures of nanoparticles （i.e., the arrangement of metal core atoms and surface ligands） by X-ray crystallography. In this perspective article, we summarize recent efforts in doping and alloying gold nanoparticles with other metals, including Pd, Pt, Ag and Cu. With atomically precise gold nanoparticles, a specific number of foreign atoms （e.g., Pd, Pt） can be incorporated into the gold core, whereas a range of Ag and Cu substitutions is observed but, interestingly, the total number of metal atoms in the homogold nanoparticle is preserved. The heteroatom substitution of gold nanoparticles allows one to probe the optical, structural, and electronic properties truly at the single-atom level, and thus provides a wealth of information for understanding the intriguing properties of this new class of nanomaterials.     

Comparative Study of Antioxidant and Catalytic Activity of Silver and Gold Nanoparticles Synthesized From Costus pictus Leaf Extract

Biological synthesis of silver and gold nanoparticles using Costus pictus leaf extract(CPLE) and their potential in vitro antioxidant and catalytic activities were reported here. Formation of Costus pictus silver(CPAgN Ps) and gold(CPAuN Ps) nanoparticles was confirmed by UV-visible spectroscopy and their spherical shape by scanning electron microscopy. The synthesized nanoparticles gave strong signals for silver and gold in energy dispersive X-ray spectroscopy. The CPAgN Ps and CPAuN Ps had an average size of 46.7and 37.2 nm, respectively, as determined by dynamic light scattering particle size analyzer. Fourier transform infrared spectroscopy(FTIR) analysis indicated involvement of amine and carbonyl groups in the formation of CPAg NPs and CPAu NPs. Thermal stability of synthesized nanoparticles was assessed by thermogravimetric analysis-differential scanning calorimetry. CPAgN Ps, CPAuN Ps and CPLE exhibited tremendous antioxidant activity when being assessed by various in vitro assays, and their activity was comparable to standard antioxidants. CPAg NPs, CPAu NPs and CPLE also caused degradation of dyes like methylene blue and methyl red. While CPAgN Ps, CPAuN Ps and CPLE caused respective 85%, 42% and 30%degradation of methylene blue, they showed less activity against methyl red. These observations signify that such green methods open up new avenues in nanobiotechnology for the synthesis of nanoparticles with extensive industrial and biomedical applications.