Alfredo R. Vilchis-Nestor

SERS properties of different sized and shaped gold nanoparticles biosynthesized under different environmental conditions by Neurospora crassa extract.

Surface-enhanced Raman scattering (SERS) is a surface-sensitive technique that enhances Raman scattering by molecules adsorbed on rough metal surfaces. It is known that metal nanoparticles, especially gold and silver nanoparticles, exhibit great SERS properties, which make them very attractive for the development of biosensors and biocatalysts. On the other hand, the development of ecofriendly methods for the synthesis of metallic nanostructures has become the focus of research in several countries, and many microorganisms and plants have already been used to biosynthesize metallic nanostructures. However, the majority of these are pathogenic to plants or humans. Here, we report gold nanoparticles with good SERS properties, biosynthesized by Neurospora crassa extract under different environmental conditions, increasing Raman signals up to 40 times using methylene blue as a target molecule. Incubation of tetrachloroauric acid solution with the fungal extract at 60°C and a pH value of a) 3, b) 5.5, and c) 10 resulted in the formation of gold nanoparticles of a) different shapes like triangles, hexagons, pentagons etc. in a broad size range of about 10-200 nm, b) mostly quasi-spheres with some different shapes in a main size range of 6-23 nm, and c) only quasi-spheres of 3-12 nm. Analyses included TEM, HRTEM, and EDS in order to corroborate the shape and the elemental character of the gold nanoparticles, respectively. The results presented here show that these ‘green’ synthesized gold nanoparticles might have potential applicability in the field of biological sensing.

Green Synthesis of Noble Metal (Au, Ag, Pt) Nanoparticles, Assisted by Plant-Extracts

The physicochemical and optoelectronic properties of metallic nanoparticles are strongly dependent on the size and size-distribution, but also nanoparticles shape contributes significantly to the control of their properties. Wide varieties of physical and chemical procedures have been developed in order to synthesize nanoparticles of different compositions, sizes, shapes and controlled polydispersity. Nevertheless, the routinely physicochemical techniques for nanoparticle production such as photochemical reduction [1], laser ablation [2], electrochemistry [3], lithography [4] or high energy irradiation [5], either remain expensive or employ hazardous substances, such as organic solvents, and toxic reducing agents like sodium borohydride and N,N-dimethylformamide. In addition, due to the high surface energy of the nanoparticles, these tend to form aggregates; therefore, surface passivating and capping reagents are frequently added to the reaction systems to avoid coalescence. The development of reliable, eco-friendly processes for the synthesis of nanomaterials is an important aspect of nanotechnology. Nanotechnology also requires the synthesis of nanomaterials of different chemical compositions, sizes and morphology with an excellent control over these characteristics.

Formation of silk-gold nanocomposite fabric using grapefruit aqueous extract

Gold nanostructures were synthesized by reduction of gold ions using aqueous extract of grapefruit pulp (Citrus paradisi). This eco-friendly bioreduction method allows the formation in solution and support of gold nanostructures on silk fibers. Bioreduction techniques involve biomolecules of grapefruit extract for reducing a gold precursor to obtain different kinds of nanostructures. Carbohydrates and organic acids, present in C. paradise, are believed to be responsible for the formation of nanoparticles. Analysis of gold–silk nanocomposites by electron microscopy shows gold nanostructures with quasi-spherical, hexagonal, and triangle shapes. The evolution of functional groups in the silk fibers before and after the bioreduction process was followed by infrared spectroscopy. Diffuse reflectance spectroscopy (DRS) and laser scanning confocal microscopy (LSCM) were used to probe surface plasmon resonance and fluorescent behavior in the silk–gold composite. This simple and novel methodology for obtaining these types of nanocomposite may have important applications in the development of functional fibers.

Effects of different amounts of APTES on physicochemical and structural properties of amino-functionalized MCM-41-MSNs

Mesoporous silica nanoparticles (MSNs) are frequently functionalized to be used for specific applications, including catalysis and biomedical engineering. In this research, MCM-41-MSNs were synthesized by the sol–gel method and were functionalized with different quantities of (3-aminopropyl) triethoxysilane (APTES) using a post-grafting method to determine the physicochemical and structural changes in the MSNs. The functionalized materials were assessed by different characterization techniques, namely, TGA, FTIR, BET, SEM, TEM, DLS, zeta potential, SAXS, XRD and XPS. The FTIR data confirmed the presence of amino groups on the MSN surfaces, and the results from the XPS, TGA and zeta potential demonstrated that the APTES concentration during post-grafting directly affects the quantity of amino groups bound to the MSNs. The SAXS, TEM and nitrogen adsorption–desorption analyses showed that as the amount of APTES in the MSNs increases, the mesoporous structure become more disordered.Graphical Abstract

Biosynthesis of silver nanoparticles using chenopodium ambrosioides

Biosynthesis of silver nanoparticles (AgNPs) was achieved using extract of Chenopodium ambrosioides as a reducer and coating agent at room temperature (25°C). Two molar solutions of AgNO3 (1mM and 10mM) and five extract volumes (0.5, 1, 2, 3, and 5 mL) were used to assess quantity, shape, and size of the particles. The UV-Vis spectra gave surface plasmon resonance at 434- 436 nm of the NPs synthesized with AgNO3 10 mM and all extract volumes tested, showing a direct relationship between extract volumes and quantity of particles formed. In contrast, the concentration of silver ions was related negatively to particle size. The smallest (4.9 ± 3.4 nm) particles were obtained with 1 mL of extract in AgNO3 10 mM and the larger amount of particles were obtained with 2 mL and 5 mL of extract. TEM study indicated that the particles were polycrystalline and randomly oriented with a silver structure face centered cubic (fcc) and fourier transform infrared spectroscopy (FTIR) indicated that disappearance of the -OH group band after bioreduction evidences its role in reducing silver ions.

Facile Solventless Synthesis of a Nylon-6,6/Silver Nanoparticles Composite and Its XPS Study

Silver nanoparticles were synthesized and supported on thin nylon membranes by means of a simple method of impregnation and chemical reduction of Ag ions at ambient conditions. Particles of less than 10 nm were obtained using this methodology, in which the nylon fibers behave as constrained nanoreactors. Pores on nylon fibres along with oxygen and nitrogen from amide moieties in nylon provide effective sites for in situ reduction of silver ions and for the formation and stabilization of Ag nanoparticles. Transmission electron microscopy (TEM) analysis showed that silver nanoparticles are well dispersed throughout the nylon fibers. Furthermore, an interaction between nitrogen of amides moieties of nylon-6,6 and silver nanoparticles has been found by X-ray photoelectron spectroscopy (XPS).

Study of the morphology of ZnS thin films deposited on different substrates via chemical bath deposition

In this work, the influence of substrate on the morphology of ZnS thin films by chemical bath deposition is studied. The materials used were zinc acetate, tri-sodium citrate, thiourea, and ammonium hydroxide/ammonium chloride solution. The growth of ZnS thin films on different substrates showed a large variation on the surface, presenting a poor growth on SiO2 and HfO2 substrates. The thin films on ITO substrate presented a uniform and compact growth without pinholes. The optical properties showed a transmittance of about 85% in the visible range of 300-800 nm with band gap of 3.7 eV.

Study of the Performance of the Organic Extracts of Chenopodium ambrosioides for Ag Nanoparticle Synthesis

There are many ways to obtain metal nanoparticles: biological, physical, and chemical ways and combinations of these approaches. Synthesis assisted with plant extracts has been widely documented. However, one issue that is under discussion refers to the metabolites responsible for reduction and stabilization that confine nanoparticle growth and prevent coalescence between nanoparticles in order to avoid agglomeration/precipitation. In this study, Ag nanoparticles were synthesized using organic extracts of Chenopodium ambrosioides with different polarities (hexane, dichloromethane, and methanol). Each extract was phytochemically characterized to identify the nature of the metabolites responsible for nanoparticle formation. With methanol extract, the compounds responsible for reducing and stabilizing silver nanoparticle were associated with the presence of phenolic compounds (flavonoids and tannins), while, with dichloromethane and hexane extracts, the responsible compounds were mainly terpenoids. Large part of the reducing activity of secondary metabolites in C. ambrosioides is closely related to compounds with antioxidant capacity, such as phenolic compounds (flavone glycoside and isorhamnetin), which are the main constituents of the methanol extracts. Otherwise, terpenoids (trans-diol, ?-terpineol, monoterpene hydroperoxides, and apiole) are the central metabolites present in dichloromethane and hexane extracts.

Silver Nanoparticles Obtained by Laser Ablation Using Different Stabilizers

We have synthesized silver nanoparticles by laser ablation in water using three stabilizers: hexadecyltrimethylammonium (CTAB) surfactant, polyamidoamine dendrimer second generation (PAMAM 2G) and polyamidoamine dendrimer fourth generation (PAMAM 4G) at different concentrations. We obtained spherical nanoparticles with narrow size distributions and average sizes ranging from 6 to 20 nm depending on the type of stabilizer and its concentration. For all cases the highest stabilizer concentration yielded the lowest average particle size; 15.5, 9.5, and 5.6 nm for CTAB, PAMAM 2G and PAMAM 4G respectively. We have also studied the stability of the nanoparticle colloids over a period of 30 days. Only the colloids of CTAB 10-3 M, all the concentrations of PAMAM 4G and pure water were stable after this time. This is explained in terms of steric hindrance of the stabilizer molecules and particle charge from Zeta potential measurements. All the results from transmission electron microscopy correlate well with those observed from the ultraviolet and visible spectra of each sample in terms of absorbance, peak width and peak maximum.

Dual function of EDTA with silver nanoparticles for root canal treatment–A novel modification

The chelating and antimicrobial capacity of a novel modification of 17% EDTA with silver nanoparticles (AgNPs) (EDTA-AgNPs) was evaluated in-vitro for root canal treatment (RCT). The EDTA-AgNPs solution was characterized by UV-Vis spectroscopy, ζ-potential and high-resolution transmission electron microscopy (HRTEM). Antimicrobial capacity was evaluated against Candida albicans and Staphylococcus aureus in planktonic and biofilm cells by broth macrodilution (24 h) and XTT assays, (1, 10 and 30 min) respectively. The chelating capacity of EDTA-AgNPs was assessed indirectly (smear layer removal) and directly (demineralizing effect) in bovine dentin at two silver concentrations, 16 and 512 μg/ml at 1 and 10 minutes of exposure time. Smear layer removal was evaluated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). The demineralizing effect was determined by atomic absorption spectroscopy (AAS), microhardness test (MH) and X-ray diffractometer (XRD). Synthesized AgNPs were quasi-spherical in shape with an average size of 13.09 ± 8.05 nm. 17% EDTA-AgNPs was effective to inhibit C. albicans and S. aureus in planktonic and biofilm cultures. The smear layer removal and demineralizing effect were similar between 17% EDTA-AgNPs and 17% EDTA treatments. The 17% EDTA-AgNPs solution proved to be an effective antimicrobial agent, and has a similar chelating capacity to 17% EDTA alone. These in-vitro studies strongly suggest that EDTA-AgNPs could be used for effective smear layer removal, having an antimicrobial effect at the same time during RCT.