Gold Nanoparticles In Colloidal Solution Research Articles

Optical properties of planar plasmon active surfaces modified with gold nanostars

The article discusses the experimental and theoretical results of studying the optical properties for planar quartz surfaces modified with gold nanostars using Surface-Enhanced Raman Spectroscopy (SERS). Surfaces functionalized with nanoparticles, prototypes of optical sensors, have been obtained. It is shown that the obtained experimental Raman signal enhancement from the dye rhodamine 6G (R6G) can be at least order 104. The paper presents the results of calculation, synthesis and study of the optical and morphological properties of such structures. A complex method for creating and evaluating the optical properties of planar nanostructures and evaluating their optical properties is proposed. The method includes the approaches based on mathematical modeling using finite differences in the time domain (FDTD - Finite-Difference Time-Domain) evaluating electromagnetic field strengths near the surfaces of star-shaped gold nanoparticles in colloidal solutions and on a silicon surface. During the simulation, we studied such parameters as the particle size, the wavelength of the exciting radiation, and the dependence of the effective amplification of the electromagnetic field on the morphological parameters of the star. The theoretical approach to the calculation of such structures is shown to be promising for the subsequent chemical synthesis described in the article and the study of optical properties. In this paper, a theoretical calculation of the parameters of the electric field and optical properties is carried out near star-shaped nanoparticles of varying sizes. These parameters were calculated by the finite difference method in the time domain. The task included finding the optimal sizes of nanoparticles as well as varying the thickness of the surface layers in order to obtain the maximum scattering values and further use of similar structures in SERS experiments. Also, within the framework of this work, syntheses of star-shaped nanoparticles was carried out, their optical and morphological properties were studied, quartz surfaces were functionalized with nanoparticles, and sensor prototypes were created in order to further assess the Raman signal amplification. Based on the results of mathematical modeling, the optimal sizes for the synthesis of star-shaped NPs were determined. Synthesis of NPs was carried out by a chemical method using seeds. To carry out the experimental part, SERS spectra were obtained using Centaur U spectrometer (OOO NanoScanTechnology, Russia). The spectrometer was equipped with three different laser sources: 632.8 nm He-Ne laser (17 mW), 532 nm and 473 nm DPSS lasers (45 mW). During the experiment, a He-Ne laser with λ = 632 nm and DPSS laser with λ = 532 nm were used to match the excitation of the plasmon maximum for the nanostars. The optical scheme of the spectrometer included an Olympus BX41 microscope (Olympus, Japan) with a 100× objective (NA 0.9) for positioning the beam and collecting scattered photons. The monochromator of the spectrometer had a focal length of 800 mm. A holographic diffraction grating of 300 gr/mm, and was equipped with a 1024×256 pixel thermoelectric cooled CCD detector (Andor Tech., UK). As a result of the paper, surfaces functionalized by nanoparticles were obtained prototypes of optical sensors. It is shown that the experimental gain of the Raman signal can be no less than 104 times. The presented data will serve as the basis for obtaining the required sizes of nanostars in the methods of the controlled chemical synthesis of colloidal nanoparticles. The results presented in the article can be applied to the development of biocompatible and highly sensitive optical sensors based on the effect of Raman scattering of light.

Effect of laser energy and pulses on size and concentration of gold nanoparticles in DDDW by LALP method

The size and the concentration of the gold nanoparticles (GNPs)synthesized in double distilled deionized water (DDDW) have beenfound to be affected by the laser energy and the number of pulses.The absorption spectra of the nanoparticles DDDW, and thesurface plasmon resonance (SPR) peaks were measured, and found tobe located between (509 and 524)nm using the UV- Visspectrophotometer. SPR calculations, images of transmissionelectron microscope, and dynamic light scattering (DLS) methodwere used to determine the size of GNPs, which found to be rangedbetween (3.5 and 27) nm. The concentrations of GNPs in colloidalsolutions found to be ranged between (37 and 142) ppm, andmeasured by atomic absorption spectroscopy (AAS).

Novel Nanoparticle-based Colorimetric Probes and Sensors for Determining Phenolic Antioxidants, Biothiols, Nitrite and Hydrogen Peroxide

This study examines the principles and milestones of nanoparticle (NP)-based colorimetric sensors and probes developed by our research group. A novel method for antioxidant capacity estimation was developed on the polyphenol-mediated growth of Ag-NPs and optical monitoring of the corresponding plasmon absorption bands. A new optical sensor using Ellman's reagent-adsorbed gold nanoparticles in colloidal solution was devised to selectively determine biothiols. Nitrite was determined by means of 4-aminothiophenol-modified Au-NPs and naphthylethylene diamine as coupling agent. Hydrogen peroxide was detected with the use of Fe3O4 magnetite NPs as peroxidase-like catalyst using a N,N-dimethyl-p-phenylenediamine (DMPD) probe.

Characterization of the Effects of 3-Aminopropyl Triethoxysilane on Stability, Optical Properties and Morphology of Colloidal Gold Nanoparticles

Aggregation of gold nanoparticles in gold colloidal solutions can be induced via the addition of an aminosilane or a change in pH. This aggregation may affect the optics, morphology and stability of these nanomaterials. Therefore, thoroughly detailing the changes will serve as a reference for individuals manipulating these parameters, especially in the field of biomedical applications and diagnostics. A systematic study utilizing several concentrations ranging from 48 mM to 475 mM of 3-aminopropyl triethoxysilane were utilized throughout the duration of the study. Ultraviolet–visible absorption spectra and photoluminescence emissions were monitored as a function of concentration and time. In addition, scanning electron and transmission electron microscopy images were taken to study the morphology. To quantify the extent of aggregation, the Nanotrac Wave (a dynamic light scattering technique) was used to determine size and size distribution of aggregates. This study demonstrates the degree to which an aminosilane could impact the stability, optics and morphology of gold nanoparticles in colloidal solutions. Ultraviolet–visible absorption spectra display systematic and extensive red shifts from 500 nm to 650 nm as the test parameters were changed. Morphology studies indicate that red shifts are largely associated with aggregation of nanoparticles as opposed to particle growth. With the addition of 3-aminopropyl triethoxysilane, the photoluminescence of the gold nanoparticles also increases as a function of concentration and time. This paper also comments on opportunities for misinterpretation of data results while using 3-aminopropyl triethoxysilane. Keywords: Aggregation, aminosilane, colloids, gold nanoparticles, morphology, optical properties.

Light-Induced Heating of Gold Nanoparticles in Colloidal Solution: Dependence on Detuning from Surface Plasmon Resonance

The absorption of light by gold nanoparticles in colloidal water solution has been studied at the simultaneous illumination of nanoparticles by the continuous wave laser beam in dependence on the detuning of laser frequency from the surface plasmon resonance. The appreciable blue shift, broadening, and increase of intensity of the plasmonic absorption band have been observed at approaching of the laser frequency to surface plasmon resonance in Au nanoparticles. The plasmon band broadening reveals the heating of gold nanoparticles that has an evident resonant character. The strong increase of nanoparticle temperature of 316 K has been obtained at moderate laser intensity of 5 × 103 W/cm2 and detuning of 28.5 nm. The sharp blue shift of plasmon band was observed when the temperature exceeded the water boiling point. Such effect is probably due to formation of the vapor bubbles around the Au nanoparticles occurring at water boiling.

Eco-friendly synthesis and characterization of gold nanoparticles using Klebsiella pneumoniae

Abstract The thrust to develop eco-friendly procedures for the production of nanoparticles arises from the extremely recent nanotechnology research. Extracellular biosynthesis of gold nanoparticles was achieved by an easy biological procedure using Klebsiella pneumoniae as the reducing agent. After exposing the gold ions to K. pneumoniae, rapid reduction of gold ions is observed foremost to the formation of gold nanoparticles in colloidal solution. UV-vis spectrum of the aqueous medium containing gold nanoparticles showed a peak around 560 nm. The crystalline nature of the particles was confirmed from an X-ray diffractometer. Transmission electron microscopy (TEM) micrograph analysis of the gold nanoparticles indicated that they were well dispersed and ranged in sizes 35 to 65 nm. The high crystalline in the FCC phase is evidenced by bright circular spots in a selected-area electron diffraction pattern and clear lattice fringes in the high-resolution TEM image. Fourier transform infrared spectroscopy revealed possible involvement of reductive groups on the surface of nanoparticles. The method exploits a cheap and easily available biomaterial not explored so far for the synthesis of metallic nanoparticles.

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.

Label free DNA detection based on gold nanoparticles quenching fluorescence of Rhodamine B

A novel and sensitive label free DNA detection method using gold nanoparticles (GNPs) and Rhodamine B (RB) has been developed. The assay is based on the following two properties. One is the different adsorption properties of single-stranded and double-stranded DNA on GNPs in colloidal solution. The other is the different quenching ability of aggregated GNPs and dispersed GNPs on RB. Un-aggregated GNPs could effectively quench the fluorescence of RB. However, the quenching ability greatly decreases after GNPs aggregated. The hybridization of probe DNA and target DNA is monitored by the fluorescence detection after the RB is added to the solution. Under the optimal experimental conditions, the detection limit of this assay is 2.9×10−13molL−1.

Kinetics and Mechanism of Single-Stranded DNA Adsorption onto Citrate-Stabilized Gold Nanoparticles in Colloidal Solution

A variety of rapid biomolecular assays under development rely on the selective adsorption of single-stranded DNA onto unfunctionalized, negatively charged, citrate-stabilized gold nanoparticles. We investigate the adsorption mechanism with a study of the binding kinetics and find strong evidence for the dominance of hydrophobic effects including linear compensation between the activation energy and the natural log of the Arrhenius prefactor and the correlation of the adsorption rate in the presence of various salts with the Hofmeister series. These results explain the selectivity for single-stranded over double-stranded DNA adsorption and contradict previous work citing an electrostatic DLVO-like mechanism. Our understanding should facilitate improvements to the selective-adsorption-based assays and, more generally, contribute to the understanding of interactions between like-charged species in aqueous solution.

Titania supported gold nanoparticles as photocatalyst

This Perspective is focused on the photocatalytic activity of gold nanoparticles supported on titania (Au/TiO(2)). Titania is the most widely used photocatalyst, but its limited activity under visible light irradiation has motivated the quest for modified titania materials absorbing visible light. The review starts by justifying how doping with metallic elements is a related strategy, but different, to that leading to the use of Au/TiO(2) in photocatalysis. Data supporting and confirming the photoactivity of gold nanoparticles in colloidal solutions are briefly presented to justify the possibility of gold photosensitization of titania by electron injection into the conduction band. After describing the most common procedures used to prepare Au/TiO(2), the central part of this article is focused on the photocatalytic activity reported for Au/TiO(2) for hydrogen generation, dye decoloration, phenol decomposition and carboxylic acid degradation, among other processes. Emphasis is given to the role that parameters like Au loading, particle size, surface area, spatial structuring and others play on the photocatalytic activity. One important issue has been to distinguish those reports using visible light from those other in which direct titania excitation by UV light has been used. These Au/TiO(2) photocatalysts can find real applications in the near future for environmental remediation and for hydrogen generation.

Label-free and homogeneous DNA hybridization detection using gold nanoparticles-based chemiluiminescence system

We find that the catalytic activity of gold nanoparticles (GNPs) on luminol-H 2O 2 chemiluminescence (CL) system is greatly enhanced after it is aggregated by 0.5 M NaCl. We use this observation to design a CL detection of DNA hybridization. It is based on that the single- and double-stranded oligonucleotides have different propensities to adsorb on GNPs in colloidal solution, and the hybridization occurred between the probe DNA and target DNA can result in aggregation of the GNPs, producing strong CL emission. In the assay, no covalent functionalization of the GNPs, the probe, or the target DNA is required. The assay, including hybridization and detection, occurs in homogenous solution. The detection limit of target DNA (3 σ) was estimated to be as low as 1.1 fM. The sensitivity was increased more than 6 orders of magnitude over that of GNPs-based colorimetric method. The present CL method for DNA hybridization detection offers the advantages of being simple, cheap, rapid and sensitive.

Fabrication of graphite nanopillars and nanocones by reactive ion etching

Self-aligned formation of graphite nanocones was carried out by oxygen-plasma etching of highly oriented pyrolytic graphite (HOPG) covered with gold nanoparticles which resulted from the immersion of HOPG samples pretreated with 3-(2-Aminoethlyamino) propyltrimethoxysilane in colloidal gold solutions. The areal density of gold nanoparticles, which determined the density of nanocones, depended on the immersion duration and the size and density of gold nanoparticles in colloidal solutions; the variation of gold-nanoparticle areal density was consistent with the ratio of sedimentation rate depending on the size and density of colloidal gold nanoparticles. However, the shapes and sizes of nanocones were controllable by manipulating the plasma-etching parameters such as plasma power and etching time. The structural examination showed that the reactive etching resulted in not only the reduction of carbon crystallites but also the increase of structural disorder. Moreover, a substantial change in the optical properties, which was indicative of the variation in electronic properties, was concomitantly observed.

Microwave-assisted deposition of uniform thin gold film on glass surface

A microwave-assisted method for rapid deposition of continuous gold films on glass substrates has been developed. Under microwave irradiation, gold nanoparticles in colloidal solutions were shown able to assemble on the naked substrates to form a gold monolayer within minutes. Images obtained by AFM revealed that the monolayer formed on the naked glass surface was much the same as that formed on the glass substrates pre-silanized with (3-aminopropyl)-trimethoxysilane. With this monolayer as seeds, further deposition of gold metal on the surface was thus possible and the thickness of the deposited gold was time-dependent as in the case of normal electroless plating. The sum time for preparing a 50-nm gold film on glass was about 15 minutes, much shorter than the existed electroless methods. Electrochemical experiments showed that the prepared gold films were continuous and can be used as stable electrodes able to sustain several hundreds of redox circulation. The quality of the films were also verified by surface plasmon resonance imaging (SPRI) studies and quite sharp pictures of protein dots were obtained, showing a smooth gold surface and proper film thickness were prepared.

Colorimetric detection of DNA sequences based on electrostatic interactions with unmodified gold nanoparticles.

We find that single- and double-stranded oligonucleotides have different propensities to adsorb on gold nanoparticles in colloidal solution. We use this observation to design a hybridization assay based on color changes associated with gold aggregation. Because the underlying adsorption mechanism is electrostatic, no covalent functionalization of the gold, the probe, or the target DNA is required. Hybridization conditions can be optimized because it is completely separated from the detection step. The assay is complete within 5 min, and <100 femtomoles of target produces color changes observable without instrumentation. Single-base-pair mismatches are easily detected.

Electrochemical determination of gold nanoparticles in colloidal solutions

A new method to determine the number concentration of gold nanoparticles in colloidal solutions is based on silver electrodeposition on the particles adsorbed on a carbon paste electrode. When colloidal gold was attached to a carbon paste electrode surface and then oxidised in a suitable media, the overpotential for cathodic deposition of silver was lowered relative to that of the carbon paste. Thus a range of potentials exists where the direct reduction of silver ions on the carbon paste surface could be avoided whilst the process did proceed on the surface of the adsorbed gold particles. A pretreated carbon paste electrode was immersed in colloidal gold solutions for 10 min. The modified electrode was then activated in a suitable media (0.1 M NaOH and 0.1 M H 2SO 4) to form oxides on the surface of gold particles. Then, silver electrodeposition at −0.12 V for 45 s followed by anodic stripping voltammetry were carried out in aqueous 1.0 M NH 3–2.0×10 −4 M AgNO 3. A linear relationship was found between the area of the anodic stripping peak and the number of colloidal gold particles cm −3 (from 3.62×10 7 to 9.06×10 8 particles cm −3) and a detection limit of 1.25×10 7 gold particles cm −3 were obtained. In addition, colloids of gold with molecules of protein (albumin) adsorbed on their particles could be determined. In this last case, a detection limit of 1.80×10 7 gold particles cm −3 was obtained.