Preparation and stabilization of monodisperse colloidal gold by reduction with aminodextran

Ultrasmall Inorganic Mesoporous Nanoparticles: Preparation, Functionalization, and Application

Ultrasmall mesoporous nanoparticles (<50 nm), a unique porous nanomaterial, have been widely studied in many fields in the last decade owing to the abundant advantages, involving rich mesopores, low density, high surface area, numerous reaction sites, large cavity space, ultrasmall size, etc. This paper presents a review of recent advances in the preparation, functionalization, and applications of ultrasmall inorganic mesoporous nanoparticles for the first time. The soft monomicelles-directed method, in contrast to the hard-template and template-free methods, is more flexible in the synthesis of mesoporous nanoparticles. This is because the amphiphilic micelle has tunable functional blocks, controlled molecule masses, configurations and mesostructures. Focus on the soft micelle directing method, monomicelles could be classified into four types, i.e., the Pluronic-type block copolymer monomicelles, laboratory-synthesized amphiphilic block copolymers monomicelles, the single-molecule star-shaped block copolymer monomicelles, and the small-molecule anionic/cationic surfactant monomicelles. This paper also reviews the functionalization of the inner mesopores and the outer surfaces, which includes constructing the yolkshell structures (encapsulated nanoparticles), anchoring the active components packed on the shell and building an asymmetric Janus architecture. Then, several representative applications, involving catalysis, energy storage, and biomedicines are presented. Finally, the prospects and challenges of controlled synthesis and large-scale applications of ultrasmall mesoporous nanoparticles in the future are foreseen.

DEAE-Dextran Coated AgNPs: A Highly Blendable Nanofiller Enhances Compressive Strength of Dental Resin Composites

Micro-crack formation and resultant bacterial infiltration are major causes of secondary caries formation in dental resin-based composite restorations. Improving dental resin composites’ mechanical and biological properties using highly bendable nanoparticles (NPs) can resolve this issue. This study aims to develop novel Diethylaminoethyl (DEAE)-Dextran silver nanoparticles (AgNPs) and subsequently modify composite resins with these NPs to enhance their mechanical and antibacterial properties. DEAE-Dextran AgNPs were successfully synthesized using a chemical reduction method that was confirmed with the help of ultraviolet-visible (UV-Vis) spectroscopy, scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Zeta potential, and energy-dispersive X-ray spectroscopy (EDS). Antibacterial activity of a composite disc with DEAE-Dextran AgNPs was tested against Streptococcus mutans, Enterococcus faecalis, and oral microcosm. The composite discs prepared with DEAE-Dextran AgNPs exhibited excellent antibacterial activity compared with composite resin reinforced by simple AgNPs (p < 0.05). Mechanical properties were significantly enhanced by adding DEAE-Dextran into composite resin (p < 0.05). Moreover, unlike AgNPs, DEAE-Dextran AgNPs were found to be less hemolytic. The results establish strong ground applications for DEAE-Dextran-modified dental composite resins in restorative dental applications.

Biologically Derived Gold Nanoparticles and Their Applications

Nanotechnology is a rapidly evolving discipline as it has a wide variety of applications in several fields. They have been synthesized in a variety of ways. Traditional processes such as chemical and physical synthesis have limits, whether in the form of chemical contamination during synthesis operations or in subsequent applications and usage of more energy. Over the last decade, research has focused on establishing easy, nontoxic, clean, cost-effective, and environmentally friendly techniques for nanoparticle production. To achieve this goal, biological synthesis was created to close this gap. Biosynthesis of nanoparticles is a one-step process, and it is ecofriendly in nature. The metabolic activities of biological agents convert dissolved metal ions into nanometals. For biosynthesis of metal nanoparticles, various biological agents like plants, fungus, and bacteria are utilized. In this review paper, the aim is to provide a summary of contemporary research on the biosynthesis of gold nanoparticles and their applications in various domains have been discussed.

Green synthesis and characterization of gold nanoparticles and their application for the rapid detection of glycyrrhizin with immunochromatographic strips

Glycyrrhizin-reduced and stabilized gold nanoparticles were used for a rapid method of detecting glycyrrhizin content.

A Review on Recent Trends in Green Synthesis of Gold Nanoparticles for Tuberculosis

Tuberculosis (TB) is a contagious disease that has affected mankind. The anti-TB treatment has been used from ancient times to control symptoms of this disease but these medications produced some serious side effects. Herbal products have been successfully used for the treatment of TB. Gold is the most biocompatible metal among all available for biomedical purposes so Gold nanoparticles (GNPs) have sought attention as an attractive biosynthesized drug to be studied in recent years for bioscience research. GNPs are used as better catalysts and due to unique small size, physical resemblance to physiological molecules, biocompatibility and non-cytotoxicity extensively used for various applications including drug and gene delivery. Greenly synthesized GNPs have much more potential in different fields because phytoconstituents used in GNP synthesis itself act as reducing and capping agents and produced more stabilized GNPs. This review is devoted to a discussion on GNPs synthesis with herbs for TB. The main focus is on the role of the natural plant bio-molecules involved in the bioreduction of metal salts during the GNPs synthesis with phytoconstituents used as antitubercular agents.

Precipitation of silver particles with controlled morphologies from aqueous solutions

Mono- and polycrystalline silver particles were formed with morphologies ranging from polyhedral, to hopper, dendritic and spherulitic particles with increasing supersaturation.

Preparation and in vivo evaluation of glyco-gold nanoparticles carrying synthetic mycobacterial hexaarabinofuranoside

A number of bacterial glycans are specific markers for the detection and the serological identification of microorganisms and are also widely used as antigenic components of vaccines. The use of gold nanoparticles as carriers for glyco-epitopes is becoming an important alternative to the traditional conjugation with proteins and synthetic polymers. In this study, we aimed to prepare and evaluate in vivo glyco-gold nanoparticles (glyco-GNPs) bearing the terminal-branched hexaarabinofuranoside fragment (Ara₆) of arabinan domains of lipoarabinomannan and arabinogalactan, which are principal polysaccharides of the cell wall of Mycobacterium tuberculosis, the causative agent of tuberculosis. In particular, we were interested whether the antibodies generated against Ara₆-GNPs would recognize the natural saccharides on the cell surface of different mycobacterial strains. Two synthetic Ara₆ glycosides with amino-functionalized spacer aglycons differing in length and hydrophilicity were directly conjugated with spherical gold nanoparticles (d = 15 nm) to give two sets of glyco-GNPs, which were used for the immunization of rabbits. Dot assays revealed cross-reactions between the two obtained antisera with the hexaarabinofuranoside and the 2-aminoethyl aglycon used for the preparation of glyco-GNPs. Both antisera contained high titers of antibodies specific for Mycobacteria as shown by enzyme-linked immunosorbent assay using M. bovis and M. smegmatis cells as antigens while there was only a weak response to M. phlei cells and no interaction with E. coli cells. The results obtained suggest that glyco-GNPs are promising agents for the generation of anti-mycobacterial antibodies.

Interaction between the photosynthetic anoxygenic microorganism Rhodobacter sphaeroides and soluble gold compounds. From toxicity to gold nanoparticle synthesis

Biological processes using microorganisms for nanoparticle synthesis are appealing as eco-friendly nanofactories. The response of the photosynthetic bacterium Rhodobacter sphaeroides to gold exposure and its reducing capability of Au(III) to produce stable gold nanoparticles (AuNPs), using metabolically active bacteria and quiescent biomass, is reported in this study. In the former case, bacterial cells were grown in presence of gold chloride at physiological pH. Gold exposure was found to cause a significant increase of the lag-phase duration at concentrations higher than 10 μM, suggesting the involvement of a resistance mechanism activated by Au(III). Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy/Energy Dispersive X-ray Spectrometry (SEM/EDS) analysis of bacterial cells confirmed the extracellular formation of AuNPs. Further studies were carried out on metabolically quiescent biomass incubated with gold chloride solution. The biosynthesized AuNPs were spherical in shape with an average size of 10 ± 3 nm, as analysed by Transmission Electron Microscopy (TEM). The nanoparticles were hydrophilic and stable against aggregation for several months. In order to identify the functional groups responsible for the reduction and stabilization of nanoparticles, AuNPs were analysed by Attenuated Total Reflectance-Fourier Transform Infrared (ATR-FTIR) spectroscopy, X-ray Photoelectron Spectroscopy (XPS), X-ray Fluorescence Spectrometry (XRF) and X-ray Absorption Spectroscopy (XAS) measurements. The obtained results indicate that gold ions bind to functional groups of cell membrane and are subsequently reduced by reducing sugars to gold nanoparticles and capped by a protein/peptide coat. Gold nanoparticles demonstrated to be efficient homogeneous catalysts in the degradation of nitroaromatic compounds.

Syntheses of gold nanoparticles and their impact on the cell cycle in breast cancer cells subjected to megavoltage X-ray irradiation

Gold nanoparticles (AuNPs) were synthesized in the presence of citrate (Au-CIT), glutathione (Au-GSH) and aminodextran (Au-DEX) in order to modify AuNPs surfaces and to increase their cellular uptake in the breast cancer cells MDA-MB-231. AuNPs were characterized with respect to their particle size, shape and colloidal stability in an aqueous solution and cell media. The mass accumulation of each AuNP type inside cancer cells was determined quantitatively, using Inductive Coupled Plasma - mass spectroscopy. The sub-cellular accumulation was studied using Transmission Electron Microscopy (TEM). It was found that gold nanoparticles applied to cancer cells were localized in cytoplasmic vesicles and that the highest uptake was shown in the presence of Au-GSH nanoparticles. The effect of AuNPs on the cell cycle was investigated using flow cytometry and Western blot analysis. The gold nanoparticles alone did not affect the cell cycle, as shown by flow cytometry. Furthermore, the cancer cells were irradiated using conventional clinically relevant high-energy X-ray radiation of 6 MV in the dose of 4 Gy. The results on cells only irradiated showed an S phase arrest six and 8 h after irradiation, and a G2/M arrest 24 and 48 h after irradiation. The irradiation of breast cancer cells treated with AuNPs has shown no significant variation in cell cycle distribution as opposed to X-ray radiation alone.

Surface-Enhanced Raman Scattering-Based Immunoassay Technologies for Detection of Disease Biomarkers

Detection of biomarkers is of vital importance in disease detection, management, and monitoring of therapeutic efficacy. Extensive efforts have been devoted to the development of novel diagnostic methods that detect and quantify biomarkers with higher sensitivity and reliability, contributing to better disease diagnosis and prognosis. When it comes to such devastating diseases as cancer, these novel powerful methods allow for disease staging as well as detection of cancer at very early stages. Over the past decade, there have been some advances in the development of platforms for biomarker detection of diseases. The main focus has recently shifted to the development of simple and reliable diagnostic tests that are inexpensive, accurate, and can follow a patient’s disease progression and therapy response. The individualized approach in biomarker detection has been also emphasized with detection of multiple biomarkers in body fluids such as blood and urine. This review article covers the developments in Surface-Enhanced Raman Scattering (SERS) and related technologies with the primary focus on immunoassays. Limitations and advantages of the SERS-based immunoassay platform are discussed. The article thoroughly describes all components of the SERS immunoassay and highlights the superior capabilities of SERS readout strategy such as high sensitivity and simultaneous detection of a multitude of biomarkers. Finally, it introduces recently developed strategies for in vivo biomarker detection using SERS.

Green and energy-efficient methods for the production of metallic nanoparticles

In the last decade, researchers paid great attention to the concept of "Green Chemistry", which aims at development of efficient methods for the synthesis of nanoparticles (NPs) in terms of the least possible impact on human life and environment. Generally, several reagents including precursors, reducing agents, stabilizing agents and solvents are used for the production of NPs and in some cases, energy is needed to reach the optimum temperature for reduction. Therefore, to develop a green approach, researchers had the opportunity to investigate eco-friendly reagents and new energy transfer techniques. In order to substitute the harmful reagents with green ones, researchers worked on different types of saccharides, polyols, carboxylic acids, polyoxometalates and extracts of various plants that can play the role of reducers, stabilizers or solvents. Also, there are some reports on using ultraviolet (UV), gamma and microwave irradiation that are capable of reducing and provide uniform heating. According to the literature, it is possible to use green reagents and novel energy transfer techniques for production of NPs. However, these new synthesis routes should be optimized in terms of performance, cost, product quality (shape and size distribution) and scale-up capability. This paper presents a review on most of the employed green reagents and new energy transfer techniques for the production of metallic NPs.

Preparation of nanosilver and nanogold based on dog rose aqueous extract

This paper describes a process of obtaining nanosilver and nanogold based on chemical reduction using substances contained in the aqueous extract of dog rose (Rosa canina). The resulting products were subjected to spectrophotometric analysis (UV-Vis), and testing of the nanoparticles' size and suspension stability was carried out by measuring the electrokinetic potential, ζ, via dynamic light scattering (DLS). Solid samples were imaged by scanning electron microscopy (SEM). The obtained data were given to statistical analysis in order to illustrate the properties of the suspension depending on the values of the input parameters: metal salts concentration, pH of the reaction mixture, and process temperature. In the course of the work, samples of nanosilver and nanogold were obtained, which were stable for over two months and which had a monomodal particle size distribution.

Gold(III) reduction by the rhizobacterium Azospirillum brasilense with the formation of gold nanoparticles

For the soil nitrogen-fixing bacterium Azospirillum brasilense, the ability to reduce [AuCl4](-) and to form gold nanoparticles (GNPs) has been demonstrated, with the appearance of a mauve tint of the culture. To validate the shapes and chemical nature of nanoparticles, transmission electron microscopy (TEM) and X-ray fluorescence analysis were used. For the widely studied agriculturally important wild-type strains A. brasilense Sp7 and Sp245, GNPs formed after 10 days of incubation of cell biomass with 0.25 mM [AuCl4](-) were shown (using TEM) to be mainly of spherical form (5 to 20 nm in diameter), with rare occasional triangles. In the course of cultivation with [AuCl4](-), after 5 days, a mauve tint was already visible for cells of strain Sp245.5, after 6 days for Sp245 and after 10 days for Sp7. Thus, for the mutant strain Sp245.5 (which has significant differences in the structure and composition of cell-surface polysaccharides as compared with Sp245), a more rapid formation of GNPs was observed. Moreover, their TEM images (also obtained after 10 days) showed different shapes: nano-sized spheres, triangles, hexagons and rods, as well as larger round-shaped flower-like nanoparticles about 100 nm in size. Since by the time of GNP formation in our experiments the cells were found to be already not viable, this confirms the dominating role of cell surface structure and chemical composition in shaping the GNPs formed in the course of [AuCl4](-) reduction to Au(0). This finding may be useful for understanding the natural biogeochemical mechanisms of gold reduction and formation of GNPs involving microorganisms. The data obtained may also help in developing protocols for environmentally friendly synthesis of nanoparticles and possible use of bacterial cells with modified surface structure and composition for their fabrication.

Photodegradable iron(III) cross-linked alginate gels

Biocompatible photoresponsive materials are of interest for targeted drug delivery, tissue engineering, 2D and 3D protein patterning, and other biomedical applications. We prepared light degradable hydrogels using a natural alginate polysaccharide cross-linked with iron(III) cations. The "hard" iron(III) cations used to cross-link the alginate hydrogel were found to undergo facile photoreduction to "soft" iron(II) cations in the presence of millimolar concentrations of sodium lactate. The "soft" iron(II) cations have a decreased ability to cross-link the alginate which results in dissolution of the hydrogel and the formation of a homogeneous solution. The photodegradation is done using long wave UV or visible light at neutral pH. The very mild conditions required for the photodegradation and the high rate at which it occurs suggest applications for iron(III) cross-linked alginate hydrogels as light-controlled biocompatible scaffolds.

Functionalized gold nanoparticles and films stabilized by in situ formed polyeugenol

Eugenol (2-methoxy-4-allyl-phenol) was used as a reducing agent for one-pot synthesis of gold nanoparticles in a mild alkaline aqueous/organic solution at room temperature. In this reaction, eugenol acts also as a stabilizing agent, since it undergoes polymerization upon oxidation. As a result, stable colloids of polyeugenol (PE)-capped gold nanoparticles are formed during the reaction with the average particle size of 44 nm. Moreover, conducting supports, such as ITO glass, are covered by Au/PE composite film when immersed in the reaction medium. The modified ITO shows redox activity assignable to residual quinone moieties of PE with redox couples at a potential range of -0.2 to 0.4V (vs. Ag/AgCl at pH 7.4). Redox properties of Au/PE nanoparticulate films can be exploited for the electrocatalytic oxidation of NADH with over 0.5 V reduction of the reaction overpotential vs. unmodified ITO. Nanoparticulate composite films were characterized by UV-vis spectroscopy, XPS and FT-IR spectroscopy. The characterization revealed structural similarity of the formed PE to lignin.

Role of base in the formation of silver nanoparticles synthesized using sodium acrylate as a dual reducing and encapsulating agent

The formation mechanism of Ag nanoparticles (NPs) synthesized with a wet-chemical reduction method using sodium acrylate as a dual reducing and capping agent was investigated with various analytical techniques. The time course of the state of the reaction solution was investigated using UV-vis and XAFS spectroscopies which showed that the NP formation rate increased with increasing concentration of sodium hydroxide (NaOH). The detailed kinetic analyses reveal that both the reduction rate of Ag ions and the nucleation rate of Ag NPs are dramatically increased with increasing NaOH concentration. XANES analyses imply that another reaction pathway via alternative Ag(+) species, such as Ag(OH)(x), was developed in the presence of NaOH. Consequently, NaOH is found to play an important role not only in creating specific intermediates in the reduction of Ag(+) to Ag(0), but also in accelerating the reduction and nucleation rates by enhancing the oxidation of sodium acrylate, thereby increasing the rate of formation of the Ag NPs.