Concentration Of Gold Nanoparticles Research Articles

Structural, thermal and electrical studies of polyethylene oxide/starch blend containing green synthesized gold nanoparticles

The green synthesis of nanoparticles has become a matter of great interest in recent times and proposed as an environmentally friendly alternative to chemical and physical methods. Blend of polyethylene oxide (PEO)/starch (70/30 wt%) doped with various concentrations of gold nanoparticles (Au NPs) were prepared by casting technique. X-ray diffraction (XRD) shows the semi-crystalline nature of all prepared samples. It also shows an increase in the amorphous region due to raising the doping level. Fourier Transform Infrared (FT-IR) spectra showed a change in intensities of OH groups and CH2 asymmetric stretching vibration after addition of gold nanoparticles, these changes were attributed to the interaction between polymeric matrix and Au NPs. Scanning electron microscopy (SEM) exhibited the partial compatibility between the polymer blend and the Au NPs. Differential scanning calorimetry (DSC) measurement indicated miscibility between the two polymers. The electrical properties were investigated via DC electrical conductivity, where found electrical conductivity increased as Au NPs content increased. The results suggest the choice of Au NPs as filler to enhance the electrical, optical, and thermal properties of PEO/starch blend.

Robust and accurate measurements of gold nanoparticle concentrations using UV-visible spectrophotometry.

This paper provides an empirical formula to calculate the extinction efficiencies of gold nanoparticles over the size range 1-1000 nm in fluids with refractive indexes which extend from n = 1 to n = 1.62. The formula contains a shape factor to account for nonspherical particles and aggregates. The empirical curves are fitted to values calculated from accurate Mie and T-Matrix theory and confirm previous descriptions which are restricted to nearly spherical particles in water of diameter between 5 and 100 nm. This paper demonstrates that these previous descriptions will be in error for fluids other than water and for nonspherical particles greater than 100 nm in size. An empirical description is provided which matches calculated values to within a few percent across most of the range. The description also matches experimental data to within the standard relative error, currently 5% at best, using other methods which directly measure the particle concentration. These extinction efficiencies can be used to validate the concentration of gold nanoparticles in a wide range of situations to support the drive for reproducibility in nanoparticle research.

A Geant4-based Monte Carlo study of a benchtop multi-pinhole X-ray fluorescence computed tomography imaging.

BackgroundX-ray fluorescence (XRF) computed tomography (XFCT) has shown promise for molecular imaging of metal nanoparticles such as gold nanoparticles (GNPs) and benchtop XFCT is under active development due to its easy access, low-cost instrumentation and operation.PurposeTo validate the performance of a Geant4-based Monte Carlo (MC) model of a benchtop multi-pinhole XFCT system for quantitative imaging of GNPs.MethodsThe MC mode consisted of a fan-beam x-ray source (125 kVp), which was used to stimulate the emission of XRF from the GNPs, a phantom (3 cm in diameter) which included six or nine inserts (3 mm in diameter), each of which contained the same (1 wt. %) or various (0.08–1 wt. %) concentrations of GNPs, a multi-pinhole collimator which could acquire multiple projections simultaneously and a one-sided or two-sided two-dimensional (2D) detector. Various pinhole diameters (3.7, 2, 1, 0.5 and 0.25 mm) and various particle numbers (20, 40, 80 and 100 billion) were simulated and the results for single pinhole and multi-pinhole (9 pinholes) imaging were compared.ResultsThe image resolution for a 1 mm multi-pinhole was between 0.88 and 1.38 mm. The detection limit for multi-pinhole operation was about 0.09 wt. %, while that for the single pinhole was about 0.13 wt. %. For a fixed number of pinholes, noise increased with decreasing number of photons.ConclusionThe MC mode could acquire 2D slice images of the object without rotation and demonstrated that a multi-pinhole XFCT imaging system could be a potential bioimaging modality for nanomedical applications.

Mitotic activity of cultured human lymphocytes treated with gold nanoparticles

Potential health and environmental effects of nanoparticles need to be thoroughly assessed before their widespread commercialization.The present investigation was planned with the aims to determine the effects of gold nanoparticles (GNPs) onblast (BI) and mitotic (MI) indices of cultured lymphocytes. The results revealed that BI (50.3 ± 2.3, 30.2 ± 1.9, 10.5 ± 0.7 and0.0%, respectively) and MI (70.1 ± 2.9, 20.4 ± 1.1, 5.3 ± 0.1 and 0.0%, respectively) showed a gradual decreased percentageas the concentration of GNPs was increased from 0.085 to 0.66 μg/mL, and the difference was significant compared to controlculture (81.6 ± 2.5 and 90.2 ± 3.7%, respectively). A maximum inhibition of BI and MI was occurred at the concentration 0.66μg/mL. In conclusion, GNPs can be considered as a growth inhibiting agent, but it is too early to reach a final conclusion inthis regard and further investigations are required to elucidate the biochemical mechanisms involved in inhibiting the mitoticactivity of lymphocytes.Key word: gold nanoparticles, mitotic index, blast index, lymphocytes

Phospholipid Bilayer Softening Due to Hydrophobic Gold Nanoparticle Inclusions.

Liposome-nanoparticle assemblies (LNAs) are vital in the context of novel targeted drug-delivery systems, in addition to investigating nanoparticle-lipid bilayer interactions. Quantifying membrane structural properties and dynamics in presence of nanoparticle inclusions provides a simple model to elucidate nanoparticle effects on membrane biophysical properties. We present experimental evidences of bilayer softening due to small hydrophobic gold nanoparticle inclusions. LNA structure has been investigated by a combination of cryo-transmission electron microscopy, dynamic light scattering, and small-angle neutron scattering. Neutron spin echo spectroscopy demonstrated a remarkable ∼15% bending modulus decrease for LNAs relative to pure liposomes. Clear dependence of bending modulus on gold nanoparticle diameter and concentration was observed from our observations. Our findings point toward local bilayer fluidization by nanoparticle inclusions leading to an overall bilayer softening. These findings add valuable information to liposomal drug-delivery vehicle design and membrane biophysics research.

Size-Defined Cracked Vesicle Formation via Self-Assembly of Gold Nanoparticles Covered with Carboxylic Acid-Terminated Surface Ligands

The self-assembly of gold nanoparticles (GNPs) into a defined structure, particularly hollow capsule structures, provides great potential for applications in materials science and medicine. However, the complexity of the parameters for the preparation of those structures through self-assembly has limited access to critical mechanistic questions. With this in mind, we have studied GNP vesicle (GNV) formation through self-assembly by the surface modification of GNPs with low-molecular-weight ligands. Here, we successfully prepared GNVs composed of GNPs with a diameter of 30 nm by surface modification with carboxylic acid-terminated fluorinated oligo(ethylene glycol) ligands (CFLs). As the carboxylic acid has two states (protonated and deprotonated), the balance of the attraction and repulsion between GNPs covered with CFLs is tunable. Sodium carboxylate-terminated fluorinated oligo(ethylene glycol) ligands (SCFLs) provided smaller GNVs than did CFLs at 0.8 × 1011 NPs/mL. Time-course study revealed that CFL-covered GNPs quickly form small aggregates and gradually grow to larger GNVs (ca. 200 nm), but no gradual growth was observed for SCFL-covered GNPs. This result indicated that the electrostatic repulsion inhibits fusion of the small GNVs. The size of the GNVs formed with the aid of CFLs was independent of the initial GNP concentration, but the extinction spectra were concentration-dependent. Electron microscopy imaging and simulations supported the defect formation in the assemblies. These results provided new insights into the vesicle formation mechanism.

Gold –graphene oxide nanocomposites for enzyme-less glucose monitoring

The enzyme-less biosensors have grabbed the attention due to the ease of handling them as they can be used in harsh environment besides being economical to use. In the present work, we have shown the synthesis and use of Gold-Graphene oxide (Au-GO) nanocomposites electrodes using glucose-capped Gold nanoparticles (Au NPs) for the enzyme-less biosensing of glucose. Glucose in Au NPs partially reduced GO present in its vicinity as evident from the characterizations, x-ray diffraction, Raman microscopy, UV–vis spectroscopy and Fourier transform infrared spectroscopy. Their structure and morphology were studied using transmission electron microscopy and scanning electron microscopy respectively. The sensitivity of Au-GO nanocomposites electrodes is 25% higher compared to enzymatic GO electrode as evident from the electrochemical measurements. The concentration of gold nanoparticles is varied for nanocomposites to understand their role in the sensing mechanism. Au-GO electrodes showed response for glucose for a wide range of concentration varying from 0.05 mM to 40 mM with linearity between 1 to 10 mM. Also, their selectivity towards glucose among the common interfering agents such as urea, cholesterol, Ascorbic acid, 4-acetaminophenol and citric acid make them suitable candidates as glucose biosensors.

Gold Nanoparticle Layers on Polystyrene Microspheres of Controlled Structure and Electrokinetic Properties.

Formation of positively charged gold nanoparticle layers on polystyrene microparticles (PSMs600) was studied using the electrokinetic and the concentration depletion methods based on atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging. Primarily, the dependence of electrophoretic mobility of microparticles on the gold nanoparticle concentration in the suspension was measured. These results were quantitatively interpreted in terms of the three-dimensional electrokinetic model. This allowed to derive a formula for calculating the coverage of nanoparticles under in situ conditions whose validity was confirmed by direct SEM imaging of deposited gold nanoparticles (AuNPs). Additionally, the maximum coverage of gold nanoparticles for various ionic strengths was determined using a concentration depletion method based on AFM imaging of residual particles deposited on the silica substrate. The maximum coverage increased with ionic strength attaining a value of 0.35 for the ionic strength of 3 × 10-3 M. This effect was attributed to the decreasing range of lateral electrostatic interactions among deposited particles. The electrokinetic properties of the gold nanoparticle layers were also evaluated in pH cycling experiments that confirmed their stability. Beyond significance to basic science, the new data acquired in this work confirm the feasibility of preparing gold nanoparticle layers on polymer microparticles characterized by a controlled structure, coverage, and electrokinetic properties.

Composite of discotic liquid crystal and gold nanoparticles: A comperative band gap study

ABSTRACTNanocomposites of discotic liquid crystal namely 2, 3, 6, 7, 10, 11-hexabutyloxytryphenylene (HAT4) in existence of variable concentration of gold nanoparticles (GNPs) have been studied at room temperature and zero pressure. The absorption spectra of nanocomposites are captured by a Shimadzu UV–VIS Spectrophotometer, model UV-1800, in the wavelength range 900–200 nm. In this paper using the Tauc’s relation, the absorption spectra fitting method was applied to estimate the optical band gap. Nanocomposites are prepared by mixing of GNPs with four concentrations in pure HAT4 viz. 0.2, 0.6, 1.2 and 3 wt%. From the investigation of absorption spectra, it has been observed that with the enhance of GNPs concentration in pure HAT4 band gap has decreased for lower concentrations but for higher concentration (3 wt%) it increases.

Investigation of energy absorption by clustered gold nanoparticles

Abstract The utilization of gold nanoparticles (GNPs) as a radiation sensitizer has received broad attention. Although GNPs form clusters in living cells, most previous simulation studies have assumed a homogeneous distribution of GNPs. In this study, a GNP cluster was constructed for simulations and the impact of cluster formation on dose enhancement was examined. Energy absorption by the GNPs was compared between clustered and homogeneous distributions for several different GNP concentrations and diameters under 100 keV X-ray irradiations. Our simulations showed that clusters more efficiently absorbed the secondary electrons and photons produced by GNPs themselves. Furthermore, the impact of cluster formation on dose enhancement was more significant for smaller GNPs and higher concentrations. Our results suggest that previous simulations assuming a homogeneous GNP distribution have overestimated the dose enhancement, especially for smaller GNPs and higher concentrations. These findings should guide the selection of GNP size and concentration for effectively optimizing dose enhancement in future studies.

Naked Gold Nanoparticles and hot Electrons in Water

The ionizing radiation in aqueous solutions of gold nanoparticles, stabilized by electrostatic non-covalent intermolecular forces and steric interactions, with antimicrobial compounds, are investigated with picosecond pulse radiolysis techniques. Upon pulse radiolysis of an aqueous solution containing very low concentrations of gold nanoparticles with naked surfaces available in water (not obstructed by chemical bonds), a change to Cerenkov spectrum over a large range of wavelengths are observed and pre-solvated electrons are captured by gold nanoparticles exclusively (not by ionic liquid surfactants used to stabilize the nanoparticles). The solvated electrons are also found to decay rapidly compared with the decay kinetics in water. These very fast reactions with electrons in water could provide an enhanced oxidizing zone around gold nanoparticles and this could be the reason for radio sensitizing behavior of gold nanoparticles in radiation therapy.

Gold nanoparticle mediated combined cancer therapy

BackgroundThe combined use of radiation therapy and chemotherapy is commonly being used in cancer treatment. The side effects of the treatment can be further minimized through targeted delivery of anticancer drugs and local enhancement of the radiation dose. Gold nanoparticles (GNPs) can play a significant role in this regard since GNPs can be used as radiation dose enhancers and anticancer drug carriers. Anticancer drug, bleomycin, was chosen as the model drug, since it could be easily conjugated onto GNPs through the gold–thiol bond.MethodsGold nanoparticles of size 10 nm were synthesized using the citrate reduction method. The surface of The GNPs was modified with a peptide sequence (CKKKKKKGGRGDMFG) containing the RGD domain and anticancer drug, bleomycin. Human breast cancer cells (MDA-MB-231) were incubated with 0.3 nM concentration of GNP–drug complex for 16 h prior to irradiation with a 2 Gy single fraction of 6 MV X-rays. After the treatment, cells were trypsinized and seeded in 60 mm dishes for clonogenic assay. Damage to DNA was probed using immunofluorescence assay.ResultsCancer cells internalized with the GNP–drug complex had a 32 ± 9% decrease in cell survival and statistically significant enhancement in DNA (deoxyribonucleic acid) damage as compared to control cells (irradiated with no GNPs) after receiving a radiation dose of 2 Gy with 6 MV photons.ConclusionsThe experimental results demonstrate that GNP-mediated chemoradiation has the potential to improve cancer care in the near future through enhancement of the local radiation dose and controlled delivery of anticancer drugs.

Segmental Mobility Studies of Poly(N-isopropyl acrylamide) Interactions with Gold Nanoparticles and Its Use as a Thermally Driven Trapping System.

Thermal desolvation of poly(N-isopropylacrylamide) (PNIPAM) in the presence of a low concentration of gold nanoparticles incorporates the nanoparticles resulting in suspended aggregates. By covalently incorporating <1% acenaphthylene into the polymerization feed this copolymer is enabled to be used as a model to study the segmental mobility of the PNIPAM backbone in response to gold nanoparticles both below and above the desolvation temperature, showing that there is a physical conformational rearrangement of the soluble polymer at ultralow nanoparticle loadings, indicating low affinity interactions with the nanoparticles. Thermal desolvation is capable of extracting >99.9% of the nanoparticles from their solutions and hence demonstrates that poly(N-isopropylacrylamide) can act as an excellent scrubbing system to remove metallic nanomaterial pollutants from solution.

Gamma irradiation of ocular melanoma and lymphoma cells in the presence of gold nanoparticles: invitro study.

The aim of this work was to determine whether conjugation of cultivated choroidal melanoma and Burkitt's lymphoma cells with gold nanoparticles (GNPs) is beneficial for these series of ocular cancer patients. GNPs are radiosensitizers and can sensitize tumors to radiotherapy.This application has been examined in several tumor types, but not in choroidal melanoma. This study shows the results of in vitro study on the choroidal melanoma and also Burkitt's lymphoma cells in the presence of GNPs during continuous gamma irradiation. Cytotoxicity of GNPs were assessed for five different concentrations then cultured melanoma and Burkitt's lymphoma cells were irradiated with a Gamma source in the presence and absence of NPs. Incubation of melanoma cells with GNP concentrations below 100 μg/ml, accompanied by gamma irradiation, increased cell death (P value = 0.016) . In the absence of irradiation, GNPs at these concentrations did not affect cultured melanoma cell metabolism. Reduced cell viability resulted from a significant increase in absorbed energy by the tumor. Moreover, GNP concentrations higher than 200 μg/ml induced cytotoxicity in melanoma cells. Cytotoxicity assay in GNPs‐loaded Burkitt's lymphoma cells showed a slight decrease in cell viability at 50 μg/ml and clear cytotoxicity at concentrations higher than 100 μg/ml (P value = 0.035). Concentration and proper injection doses of GNPs in sensitive tissues such as the human eye are important variables yet to be determined.This is the first report of choroidal melanoma dosimetry performed in the presence of GNPs and provides valuable insights into future therapeutic approaches. Further in vitro study with more different sizes and concentrations is needed to determine the optimum size and concentration before any clinical research in this regard.

Heterogeneous local order in self-assembled nanoparticle films revealed by X-ray cross-correlations.

We report on the self-assembly of gold nanoparticles coated with a soft poly(ethylene glycol) shell studied by X-ray cross-correlation analysis. Depending on the initial concentration of gold nanoparticles used, structurally heterogeneous films were formed. The films feature hot spots of dominating four- and sixfold local order with patch sizes of a few micrometres, containing 104-105 particles. The amplitude of the order parameters suggested that a minimum sample amount was necessary to form well ordered local structures. Furthermore, the increasing variation in order parameters with sample thickness demonstrated a high degree of structural heterogeneity. This wealth of information cannot be obtained by the conventional microscopy techniques that are commonly used to study nanocrystal superstructures, as illustrated by complementary scanning electron microscopy measurements.

Effect of reinforcement of acrylic resin by nanosilver and nanogold on water sorption and solubility

Purpose: The objective of the study was to assess the antimicrobial activity of acrylic denture base containing nanosilver and nanogold to; S. aureus, E. coli and C. albicans. Methods: Three concentrations of silver and gold nanoparticles (0.01 %, 0.1%, 1% of polymer weight) were added to MMA monomer, cured samples of modified PMMA were evaluated for their antimicrobial activity to three micro-organisms using Broth Microdilution Assay. Results: Both nanosilver and nanogold showed antimicrobial activity to the tested micro-organisms. Conclusion: Addition of nanogold and nanosilver to acrylic bases could improve their antimicrobial activity.

Microbiological evaluation of acrylic resin modified with silver and gold nanoparticles

Purpose: The objective of the study was to assess the antimicrobial activity of acrylic denture base containing nanosilver and nanogold to; S. aureus, E. coli and C. albicans. Methods: Three concentrations of silver and gold nanoparticles (0.01 %, 0.1%, 1% of polymer weight) were added to MMA monomer, cured samples of modified PMMA were evaluated for their antimicrobial activity to three micro-organisms using Broth Microdilution Assay. Results: Both nanosilver and nanogold showed antimicrobial activity to the tested micro-organisms. Conclusion: Addition of nanogold and nanosilver to acrylic bases could improve their antimicrobial activity. Key words: Nanosilver, Nanogold, Antimicrobial activity.

A Monte Carlo Study on Dose Enhancement by Homogeneous and Inhomogeneous Distributions of Gold Nanoparticles in Radiotherapy with Low Energy X-rays.

To enhance the dose to tumor, the use of high atomic number elements has been proposed. The aim of this study is to investigate the effect of gold nanoparticle distribution on dose enhancement in tumor when the tumor is irradiated by typical monoenergetic X-ray beams by considering homogeneous and inhomogeneous distributions of gold nanoparticles (GNPs) in the tumor. MCNP-4C Monte Carlo code was utilized for the simulation of a source, a phantom containing tumor and gold nanoparticles with concentrations of 10, 30 and 70 mg Au/g tumor. A 15 cm×15 cm×15 cm cubic water phantom was irradiated with a small planar source with four monoenergetic X-ray beams of 35, 55, 75 and 95 keV energy. Furthermore, tumor depths of 2.5 cm, 4.5 cm and 6.5 cm with homogeneous and inhomogeneous distributions of nanoparticles were studied. Each concentration, photon energy, tumor depth and type of distribution was evaluated in a separate simulation. Results have shown that dose enhancement factor (DEF) in tumor increases approximately linearly with the concentration of gold nanoparticles. While DEF has fluctuations with photon energy, 55 keV photons have the highest DEF values compared to other energies. While DEF has relatively the same values with tumor located at various depths, inhomogeneous distribution of GNP has shown different results compared with the homogeneous model. Dose enhancement can be expected with relatively deep seated tumors in radiotherapy with low energy X-rays. Inhomogeneous model is recommended for the purpose of dose enhancement study because it mimics the real distribution of GNPs in tumor.

Confined Growth of ZIF‐8 Nanocrystals with Tunable Structural Colors

AbstractZeolitic imidazolate frameworks (ZIF‐8) have promising applications as sensors or catalysts due to their highly porous crystalline structures. While most of the previous studies are based on ZIF‐8 crystals either in isolated particles in aqueous environments or in a compact colloidal form, here a facile method is reported to achieve wafer‐based isolated ZIF‐8 nanocrystals to facilitate their integration in microsystems and as surface coatings for catalysis. The fabrication process includes the growth of compact zinc oxide film by atomic layer deposition that functions as the Zn source for the ZIF‐8 synthesis, and the dispersion of gold nanoparticles as inhibitors for the following crystallization transformation of ZIF‐8 crystals. By choosing the concentration of gold nanoparticles, the density of ZIF‐8 nanocrystals can be controlled and the sizes of individual ZIF‐8 crystals can be scaled down to ≈100 nm. A wide range of structural colors generated by the ZIF‐8 nanocrystals is also observed, which can be attributed to the size‐dependent resonant scattering as verified by finite‐difference time‐domain simulations and classical Mie theory. The scalable fabrication of wafer‐based ZIF‐8 nanocrystals empowered with tunable optical properties paves a new way to explore the promising applications in nanophotonics and bionanotechnology.

Reduced graphene oxide supported gold nanoparticles for electrocatalytic reduction of carbon dioxide

Electrochemical reduction of carbon dioxide is one of the methods which have the capability to recycle CO2 into valuable products for energy and industrial applications. This research article describes about a new electrocatalyst “reduced graphene oxide supported gold nanoparticles” for selective electrochemical conversion of carbon dioxide to carbon monoxide. The main aim for conversion of CO2 to CO lies in the fact that the latter is an important component of syn gas (a mixture of hydrogen and carbon monoxide), which is then converted into liquid fuel via well-known industrial process called Fischer-Tropsch process. In this work, we have synthesized different composites of the gold nanoparticles supported on defective reduced graphene oxide to evaluate the catalytic activity of reduced graphene oxide (RGO)-supported gold nanoparticles and the role of defective RGO support towards the electrochemical reduction of CO2. Electrochemical and impedance measurements demonstrate that higher concentration of gold nanoparticles on the graphene support led to remarkable decrease in the onset potential of 240 mV and increase in the current density for CO2 reduction. Lower impedance and Tafel slope values also clearly support our findings for the better performance of RGOAu than bare Au for CO2 reduction.