The effect of the deposition parameters on size, distribution and antimicrobial properties of photoinduced silver nanoparticles on titania coatings

Controlled photodeposition of silver nanoparticles (AgNP) on titania coatings using two different sources of UV light is described. Titania (anatase) thin films were prepared by the sol-gel dip-coating method on silicon wafers. AgNPs were grown on the titania surface as a result of UV illumination of titania films immersed in aqueous solutions of silver nitrate. UV xenon lamp or excimer laser, both operating at the wavelength 351 ± 5 nm, was used as illumination sources. The AFM topography of AgNP/TiO₂ nanocomposites revealed that silver nanoparticles could be synthesized by both sources of illumination, however the photocatalysis carried out by UV light from xenon lamp illumination leads to larger AgNP than those synthesized using the laser beam. It was found that the increasing concentration of silver ions in the initial solution increases the number of Ag nanoparticles on the titania surface, while longer time of irradiation results the growth of larger size nanoparticles. Antibacterial tests performed on TiO₂ covered by Ag nanoparticles revealed that increasing density of nanoparticles enhances the inhibition of bacterial growth. It was also found that antibacterial activity drops by only 10-15% after 6 cycles compared to the initial use.     

Preparation and bactericide activity of gallic acid stabilized gold nanoparticles

In this work, gold nanoparticles with three different sizes (13.7, 39.4, and 76.7 nm) were prepared using a simple aqueous method with gallic acid as the reducing and stabilizing agent, the different sizes were obtained varying some experimental parameters as the pH of the reaction and the amount of the gallic acid. The prepared nanoparticles were characterized using X-ray diffraction, transmission electron microscopy, dynamic light scattering, and UV–Vis spectroscopy. Samples were identified as elemental gold and present spherical morphology, a narrow size distribution and good stabilization according to TEM and DLS results. The antibacterial activity of this gallic acid stabilized gold nanoparticles against S. mutans (the etiologic agent of dental caries) was assessed using a microdilution method obtaining a minimum inhibitory concentration of 12.31, 12.31, and 49.25 μg/mL for 13.7, 39.4, and 76.7 nm gold nanoparticles, respectively. The antibacterial assay showed that gold nanoparticles prepared in this work present a bactericide activity by a synergistic action with gallic acid. The MIC found for this nanoparticles are much lower than those reported for mixtures of gold nanoparticles and antibiotics.     

Raman spectra of benzoic acid enhanced by the silver nanoparticles of various sizes

Using sodium borohydride as the reducing agent and polyvinyl pyrrolidone (PVP, MW = 10 000) as the stabilizer, we obtained silver nanoparticles of various diameters (8–78 nm) from silver nitrate aqueous solutions in the concentration range from 0.001 to 0.1 M. The surface‐enhanced Raman scattering (SERS) from benzoic acid's ring‐breathing mode at 1003 cm⁻¹ was detected from its dilute solutions (∼10⁻² M) doped with these silver nanoparticles under 488‐nm laser excitation. The observed size dependences of SERS intensities fit quite well with those calculated by Schatz's theoretical model for spherical silver nanoparticles. The only exception occurred with the smallest particles (8 nm), possibly due to the failure of Maxwell's electromagnetic theory used in this model. Copyright © 2009 John Wiley & Sons, Ltd.     

Zinc sulfide nanoparticles: Spectral properties and photocatalytic activity in metals reduction reactions

Formation of zinc sulfide nanocrystals in aqueous solutions of various polymers has been studied. Spectral properties of ZnS nanoparticles have been investigated, the structure of the long-wave edge of the fundamental absorption band of ZnS nanocrystals has been analyzed. It has been shown that the variation of the synthesis conditions (stabilizer nature and concentration, solution viscosity, ZnS concentration, etc.) allows tailoring of the ZnS nanocrystals size in the range of 3–10 nm. Photochemical processes in colloidal ZnS solutions, containing zinc chloride and sodium sulfite, have been investigated. It has been found that the irradiation of such solutions results in the reduction of Zn(II), the rate of this reaction growing at a decrease in the size of ZnS nanoparticles. Kinetics of photocatalytic Zn(II) reduction has been studied. It has been concluded that two-electron reduction of adsorbed Zn(II) species is the rate-determining stage of this reaction. Photocatalytic activity of ZnS nanoparticles in KAu(CN)₂ reduction in aqueous solutions has been discovered. Spectral characteristics and kinetics of ZnS/Au⁰ nanocomposite formation have been studied. It has been shown that the photoreduction of gold(I) complex is the equilibrium reaction due to the reverse oxidation of gold nanoparticles by ZnS valence band holes.     

Monodisperse Polypyrrole Nanoparticles Prepared via γ‐Ray Radiolysis of Water: An Efficient Near‐Infrared Photothermal Agent for Cancer Therapy

Biosafe nanoparticles with strong near‐infrared (NIR) light photothermal conversion effect can bring effective hyperthermia as one of the promising approaches in cancer therapy. In this work, a new facile and green preparation method of polypyrrole (PPy) nanoparticles based on ⁶⁰Co γ‐ray radiation on a simple air‐saturated strong acidic aqueous solution of pyrrole (pH ≤ 1) is studied. According to the MCAP‐FACSIMILE simulation on the concentrations of the radiolysis products of water at the presence of H⁺ and O₂, the main strong oxidative radiolysis products · OH and H₂O₂ rapidly induce the polymerization of pyrrole. The size of the prepared PPy nanoparticles is about several tens of nanometers and can be controlled by the pH, the concentration of the stabilizer poly(vinyl alcohol), and the absorbed dose rate (the amount of energy absorbed per unit mass of the irradiated material within per unit of time). The PPy nanoparticles show rapid and remarkable NIR (808 nm) photothermal conversion efficiency up to 40.1% in water. Furthermore, the in vitro and in vivo experiments confirm that the prepared PPy nanoparticles exhibit enough strong NIR photothermal effect in tumor cells (4T1 and HeLa) and show a promising prospect as the NIR photothermal agent for the future cancer therapy.     

Gold nanoflowers with mesoporous silica as “nanocarriers” for drug release and photothermal therapy in the treatment of oral cancer using near-infrared (NIR) laser light

In this experiment, we successfully developed nanocarriers in the form of gold nanoflowers coated with two layers of silica for the purposes of drug loading and NIR (near-infrared) photothermal therapy for the treatment of oral cancer. The gold nanoflowers converted NIR laser energy into heat energy. The cores were coated with a thin silica layer (AuNFs@SiO₂) to protect the gold nanoflowers from intraparticle ripening. The second layer was mesoporous silica (AuNFs@SiO₂@mSiO₂), which acted as a nanocarrier for anticancer drug (DOX) loads. The mean effective diameter of the nanoparticles was approximately 150–200 nm, whereas the peak absorption of the AuNFs was 684 nm. After the AuNFs were encapsulated by the silica shells, the plasmonic absorption peak of AuNFs@SiO₂ and AuNFs@SiO₂@mSiO₂ exhibited a red shift to 718 nm. When exposed to an 808 nm NIR laser, these crystals showed an obvious photothermal conversion in the NIR region and a highly efficient release of DOX. Biocompatibility was assessed in vitro using Cell Counting Kit-8 assays, and the results showed that the nanocarriers induced no obvious cytotoxicity. This nanomaterial could be considered a new type of material that shows promising potential for photothermal-chemotherapy against malignant tumours, including those of oral cancers.     

Green synthesis of gold and silver nanoparticles using gallic acid: catalytic activity and conversion yield toward the 4-nitrophenol reduction reaction

In the present report, gallic acid was used as both a reducing and stabilizing agent to synthesize gold and silver nanoparticles. The synthesized gold and silver nanoparticles exhibited characteristic surface plasmon resonance bands at 536 and 392 nm, respectively. Nanoparticles that were approximately spherical in shape were observed in high-resolution transmission electron microscopy and atomic force microscopy images. The hydrodynamic radius was determined to be 54.4 nm for gold nanoparticles and 33.7 nm for silver nanoparticles in aqueous medium. X-ray diffraction analyses confirmed that the synthesized nanoparticles possessed a face-centered cubic structure. FT-IR spectra demonstrated that the carboxylic acid functional groups of gallic acid contributed to the electrostatic binding onto the surface of the nanoparticles. Zeta potential values of ?41.98 mV for the gold nanoparticles and ?53.47 mV for the silver nanoparticles indicated that the synthesized nanoparticles possess excellent stability. On-the-shelf stability for 4 weeks also confirmed that the synthesized nanoparticles were quite stable without significant changes in their UV–visible spectra. The synthesized nanoparticles exhibited catalytic activity toward the reduction reaction of 4-nitrophenol to 4-aminophenol in the presence of sodium borohydride. The rate constant of the silver nanoparticles was higher than that of the gold nanoparticles in the catalytic reaction. Furthermore, the conversion yield (%) of 4-nitrophenol to 4-aminophenol was determined using reversed-phase high-performance liquid chromatography with UV detection at 254 nm. The silver nanoparticles exhibited an excellent conversion yield (96.7–99.9 %), suggesting that the synthesized silver nanoparticles are highly efficient catalysts for the 4-nitrophenol reduction reaction.     

Extremophilic Polysaccharide for Biosynthesis and Passivation of Gold Nanoparticles and Photothermal Ablation of Cancer Cells

Extremophiles are the group of organisms that are far overlooked for exploring novel biomaterials in the field of material science and bionanotechnology. Extremophilic bacterial‐sulfated exopolysaccharide, mauran (MR), is employed for the bioreduction and passivation of gold nanoparticles (AuNps) to enhance the biocompatibility of AuNps and used for photothermal ablation of cancer cells. Here, various concentrations of MR solution are tested for the reduction of HAuCl₄ solution in the presence as well as in the absence of an external reducing agent, to produce mauran‐gold nanoparticles (MRAu Nps). These biocompatible nanocomposites are treated with cancer cell lines under in vitro conditions and NIR irradiated for complete ablation. MRAu Nps‐treated cancer cells on immediate exposure to infrared radiation from a femtosecond pulse laser of operating wavelength 800 nm are subjected to hyperthermia causing cell death. Biocompatible MR stabilization could fairly reduce the cytotoxicity caused by bare AuNps during biomedical applications. Application of a biocompatible polysaccharide from extremophilic bacterial origin for reduction and passivation of AuNps and used for a biomedical purpose is known to be first of its kind in bionanofusion studies.     

Titania Gold Composite: Effect of Illumination on Size of Gold Nanoparticles with Consequent Implication on Photocatalytic Water Splitting

This work deals with the study of photodeposition (PD) of gold nanoparticles (AuNPs) on TiO₂ by using different illumination sources, Medium pressure Mercury lamp (ML), Solar Simulator equipped with AM 1.5 (SL) and Tungsten lamp (WL). Different particle size of AuNPs on TiO₂ were obtained by photodeposition method under different illumination sources, which clearly proves the influence of light source on the synthesis of Au–TiO₂. The plasmonic activity of Au–TiO₂ photocatalyst for water splitting reaction was observed to be strongly influenced by the particle size of Au as well as illumination source. Amongst the three different illumination sources used, smallest particle size for AuNP–TiO₂ were observed under ML followed by SL and WL, as revealed by TEM analysis. Different illumination sources were also investigated to evaluate the activity of Au–TiO₂ samples thus prepared under different illumination conditions. The order of hydrogen evolution rate (HER) observed for Au–TiO₂ with different source of illuminations is ML > SL > WL. The highest HER of 1709 μmol/h was observed for Au–TiO₂, which was synthesized and evaluated under ML irradiation. This may be explained on the basis of reduced catalytic activity and photothermal effect of Au nanoparticles with increasing particle size.     

Size,Shape, and Wavelength Effect on Photothermal Heat Elevation of Gold Nanoparticles: Absorption Coefficient Experimental Measurement

Complex-shaped nanoparticles as gold nanourchins (GNU) and nanorods (GNR) are very suitable agents in the case of photothermal therapy due to their photon-heat conversion ability in the red and near-infrared region (NIR). The quantification in heat generation of complex shaped nanostructures is an important key to predict the therapeutic effect of these nanoparticles. For that, the determination of the nanoparticles absorption cross section (σ_Abs) responsible for the heat generation is one of the important steps before any application. Although it is obvious to determine σ_Abs for spheres via Mie's theory, in the case of complex structures like GNU or GNR, this parameter is difficult to model. In this work, a new methodology is used to determine experimentally σ_Abs for both GNU and GNR. Experimental measurements of the photothermal properties of 100 nm size GNU and two different sizes of GNRs are studied regarding different parameters such as concentration, laser excitation wavelength, and exposure time. By using the heat transfer theory, the temperature elevation in the nanoparticles solutions is converted to temperature elevation at the nanoparticles surface and σ_Abs values are then calculated for both GNU and GNR in the NIR spectral region.     

Shape-controlled Synthesis of Gold Nanoparticles from Gold(III)-chelates of β-diketones

Chelating ligands with β-diketone skeleton have been employed for the first time as reductant to produce ligand stabilized gold nanoparticles of different shapes out of aqueous HAuCl₄ solutions. Evolution of stable gold nanoparticles happens to be first order with respect to gold particles having rate constants ∼ ∼10⁻² min⁻¹ and subsequent chlorine insertion in the β-diketone skeleton is reported as a general feature. Spherical or triangular or hexagonal particle evolution goes selectively under the influence of different β-diketones in terms of capping and reducing capabilities of the reductants.     

Effect of reducing agent in the formation of CdSe nanoparticles by chemical reduction route

CdSe nanoparticles were synthesized using a simple chemical reduction route at room temperature. Nanoparticle size was controlled by the amount of reducing agent and was characterized by TEM and TED. With increased amounts of sodium borohydride as a reducing agent, the size of the nanoparticles decreased. Size of the nanoparticles varies between 5 and 12 nm with a size dispersion of 1.5 nm. The grown sample was ultra-sonicated in ethanol. The dispersed sample was characterized structurally, optically and electrically. The long-duration photoconductive decay at room temperature shows exponential variation under weak illumination.     

Noninvasive Temperature Measurement in Dental Materials Using Nd3+, Yb3+ Doped Nanoparticles Emitting in the Near Infrared Region

In this work, the application of near infrared (NIR)-emitting NaYbF₄:1%Tm³⁺@NaLuF₄:30%Nd³⁺ core–shell nanoparticles is reported for noninvasive probing and monitoring the temperature during photopolymerization of dental materials. When excited at 808 nm, the synthesized nanoparticles emit NIR photoluminescence (PL) with two distinctive peaks at 865 and 980 nm which correspond to radiative transitions from the doped Nd³⁺ and Yb³⁺ ions, respectively. Luminescence intensity ratio between these two bands is found to vary with temperature due to temperature-dependent electronic excitation energy transfer between Nd³⁺ and Yb³⁺ ions at the core/shell interface. This finding allows luminescence ratiometric evaluation of the in situ temperature during photopolymerization of resin cement (doped with nanoparticles) in a veneer placement procedure. In addition, the NIR emission also enables PL imaging of the distribution of the adhesive under the veneer. The results highlight that rare-earth ions–doped nanoparticles with both excitation and emission in the NIR spectral range are advantageous for both PL-based nanothermometry and imaging due to the reduced attenuation of NIR light by dental ceramics.     

Subdiffraction scattered light imaging of gold nanoparticles using structured illumination

A reflective light-scattering (RLS) microscope with structured illumination (SI) provides subdiffraction resolution and improves the image quality of gold nanoparticles in biological systems. The three-dimensional (3D)-structured pattern is rapidly and precisely controlled with a spatial light modulator and scrambled at the conjugate image plane to increase spatial incoherence. The reconstructed SI-RLS image of 100?nm gold nanoparticles reveals lateral and axial resolutions of approximately 117 and 428?nm. We present a high-resolution image of gold nanoparticles inside a HeLa cell, with improved contrast.     

Efficient one-pot synthesis of Ag nanoparticles loaded on N-doped multiphase TiO2 hollow nanorod arrays with enhanced photocatalytic activity

The simultaneous Ag loaded and N-doped TiO₂ hollow nanorod arrays with various contents of silver (Ag/N-THNAs) were successfully synthesized on glass substrates by one-pot liquid phase deposition (LPD) method using ZnO nanorod arrays as template. The catalysts were characterized by Raman spectrum, field-emission scanning electron microscopy (FESEM), high-resolution transmission electron microscope (HRTEM), ultraviolet-vis (UV-vis) absorption spectrum and X-ray photoelectron spectroscopy (XPS). The results suggest that AgNO₃ additive in the precursor solutions not only can promote the anatase-to-rutile phase transition, but also influence the amount of N doping in the samples. The photocatalytic activity of all the samples was evaluated by photodegradation of methylene blue (MB) in aqueous solution. The sample exhibited the highest photocatalytic activity under UV light illumination when the AgNO₃ concentration in the precursor solution was 0.03 M, due to Ag nanoparticles acting as electron sinks; When the AgNO₃ concentration was 0.07 M, the sample performed best under visible light illumination, attributed to the synergetic effects of Ag loading, N doping, and the multiphase structure (anatase/rutile).     

Acoustic cavitation for engineering of gold sols in silver nitrate solutions

Binary gold-silver nanostructures of preformed gold nanoparticles (25nm) in silver nitrate solutions are produced by a two step sonication (20kHz). Ultrasonic treatment of gold-silver mixtures is carried out in the presence of sodium dodecyl sulfate in water or 2-propanol, and poly(vinyl pyrrolidone) in ethylene glycol solutions. Gold-silver nano-worms, which consist of ripened gold particles connected by ultrasonically reduced silver, are formed after 1h of sonication in the presence of sodium dodecyl sulfate aqueous solution. In 2-propanol bimetallic nano-worms have a well defined core-shell structure. Polygonal alloy nanoparticles with gold as a core material and a silver shell are produced after 180min of sonication in the presence of poly(vinyl pyrrolidone) in ethylene glycol solution. Bimetallic gold-silver nanostructures have defected face centered cubic structure and represent polycrystals with a large number of crystallites randomly oriented. For the first time, the mechanism of gold particle design by ultrasound is examined in detail. The role of additives (sodium dodecyl sulfate, polyvinyl pyrrolidone, ethylene glycol and 2-propanol) as reductants of silver at the gold contact surface or stabilizers of particles is highlighted.     

Effect of Particle Size and Phase Composition of Titanium Dioxide Nanoparticles on the Photocatalytic Properties

Titanium dioxide (TiO₂) nanoparticles were prepared by the oxidation of titanium tetrachloride (TiCl₄) in a diffusion flame reactor. The average diameter of particles was 15–30 nm and mass fraction of anatase ranged from 40% to 80%. Effects of particle size and phase composition of those TiO₂ nanoparticles on photocatalytic properties such as decomposition of methylene blue, bacteria and ammonia gas were investigated. The degree of decomposition of methylene blue by the TiO₂ nanoparticles under the illumination of the black light was directly proportional to the anatase mass fraction, but inversely to the particle size. The decomposition of bacteria and ammonia gas by the TiO₂ nanoparticles under the illumination of the fluorescent light showed the same trend as in the case of the methylene blue.     

Synthesis and nonlinear light scattering of microemulsions and nanoparticle suspensions

Microemulsions composed of normal or inverse micellar solutions and aqueous suspensions of pristine (uncoated) or silica-coated iron oxide nanoparticles, mainly γ-Fe₂O₃, were synthesised and their optical limiting properties investigated. The microemulsions are colorless solutions with high transparency for visible wavelengths while the aqueous suspensions of iron oxide are of pale yellow colour. Optical limiting experiments performed in 2 mm cells using a f/5 optical system with a frequency doubled Nd:YAG laser delivering 5 ns pulses with 10 Hz repetition rate, showed clamping levels of ∼3 μJ for the suspensions of both pristine and silica-coated iron oxide nanoparticles. A strong photoinduced nonlinear light scattering was observed for the water-in-oil microemulsion and the aqueous suspensions of nanoparticles while oil-in-water microemulsions did not show a significant nonlinear effect. Measurements carried out using an integrating sphere further verified that the photoinduced nonlinear light scattering is the dominating nonlinear mechanism while the nonlinear absorption of iron oxide nanoparticles is negligible at 532 nm.     

Laser ablation of silver and gold in liquid ammonia

Laser ablation of a silver (Ag) and/or gold (Au) target was performed in liquid ammonia (l-NH₃) at 233 K using nanosecond laser pulses of 1064, 532 and 355 nm wavelengths. An “in situ” monitoring of the ablation process by UV/vis/NIR spectroscopy has shown the evolution of the surface plasmon extinction band of silver or gold nanoparticles and thus confirmed their formation. While sols of Au nanoparticles in l-NH₃ are quite stable in air, those of Ag nanoparticles undergo oxidation to Ag(I) complexes with NH₃ ligands. On the other hand, formation of solvated electrons, namely of the (e⁻)NH₃ solvates, has not been unequivocally confirmed under the conditions of our laser ablation/nanoparticle fragmentation experiment, since only very weak vis/NIR spectral features of these solvates were observed with a low reproducibility. Reference experiments have shown that the well-known chemical production of these solvates is hindered by the presence of Ag and Au plates. Ag and Au targets can thus possibly act as electron scavengers in our ablation experiments.     

Sonosynthesis of gold nanoparticles from a geranium leaf extract

A rapid in situ biosynthesis of gold nanoparticles (AuNPs) is proposed in which a geranium (Pelargonium zonale) leaf extract was used as a non-toxic reducing and stabilizing agent in a sonocatalysis process based on high-power ultrasound. The synthesis process took only 3.5 min in aqueous solution under ambient conditions. The stability of the nanoparticles was studied by UV–Vis absorption spectroscopy with reference to the surface plasmon resonance (SPR) band. AuNPs have an average lifetime of about 8 weeks at 4 °C in the absence of light. The morphology and crystalline phase of the gold nanoparticles were characterized by transmission electron microscopy (TEM). The composition of the nanoparticles was evaluated by electron diffraction and X-ray energy dispersive spectroscopy (EDS). A total of 80% of the gold nanoparticles obtained in this way have a diameter in the range 8–20 nm, with an average size of 12 ± 3 nm. Fourier transform infrared spectroscopy (FTIR) indicated the presence of biomolecules that could be responsible for reducing and capping the biosynthesized gold nanoparticles. A hypothesis concerning the type of organic molecules involved in this process is also given. Experimental design linked to the simplex method was used to optimize the experimental conditions for this green synthesis route. To the best of our knowledge, this is the first time that a high-power ultrasound-based sonocatalytic process and experimental design coupled to a simplex optimization process has been used in the biosynthesis of AuNPs.