Gold Nanoparticles In Presence Research Articles

Aggregation of Gold Nanoparticles in Presence of the Thermoresponsive Cationic Diblock Copolymer PNIPAAM48-b-PAMPTMA6.

The adsorption of the thermoresponsive positively charged copolymer poly(N-isopropylacrylamide)-block-poly(3-acrylamidopropyl)trimethylammonium chloride, PNIPAAM48-b-PAMPTMA6(+), onto negatively charged gold nanoparticles can provide stability to the nanoparticles and make the emerging structure tunable by temperature. In this work, we characterize the nanocomposite formed by gold nanoparticles and copolymer chains and study the influence of the copolymer on the expected aggregation process that undergoes those nanoparticles at high ionic strength. We also determine the lower critical solution temperature (LCST) of the copolymer (around 42 °C) and evaluate the influence of the temperature on the nanocomposite. For those purposes, we use dynamic light scattering, UV-vis spectroscopy and transmission electron microscopy. At the working PNIPAAM48-b-PAMPTMA6(+) concentration, we observe the existence of copolymer structures that trap the gold nanoparticles and avoid the formation of nanoparticles aggregates. Finally, we discuss how these structures can be useful in catalysis and nanoparticles recovery.

A comparative study of heat transfer analysis on ethylene glycol or engine oil as base fluid with gold nanoparticle in presence of thermal radiation

The present work addresses to analyse the heat transfer enhancement of unsteady laminar incompressible MHD flow of couple stress nanofluid through a rectangular squeezing channel with thermal radiation. The governing transport equations are reduced into an ordinary differential equation using relevant similar transformations and then solved numerically with the shooting method Runge–Kutta fourth-order scheme. The results are sketched as two-dimensional graphs and explained in detail for flow and heat transfer with non-dimensional physical parameters. Further calculated the skin friction and heat transfer rates at the upper plate. The axial velocity of engine oil/ethylene glycol has been increased by β and Da−1 towards the centre of the channel decreased for squeezing, and it is opposite for the separation case. The numerical results have good agreement with published work for temperature profile.

Improvement of adsorptive voltammetric methods for determination of Midodrine by carbon paste electrode modified with gold nano particles in presence of β-cyclodextrin

An effective novel electrochemical sensor constructed for the determination of Midodrine hydrochloride drug using differential pulse voltammetry. The sensor is based on a carbon paste electrode modified with gold nanoparticles and β-cyclodextrin in Britton-Robinson buffer of pH 3.0. The effect of various experimental parameters on the constructed electrodes properties including pH, β-cyclodextrin concentration and scan rate was investigated. At the optimum conditions, a linear range from 3.0 x 10-6 to 3.2 x 10-4 mol L-1 with correlation coefficient of 0.9997 and a detection limit of 5.14 x 10-7 mol L-1were obtained. The modified electrodes were used for microdetermination of the drug in tablets and spiked human urine samples with appropriate an acceptable recovery, reproducibility, selectivity and robustness. Potential strength investigation was achieved using 0.1 M of HCl.

Aggregation of cysteamine-capped gold nanoparticles in presence of ATP as an analytical tool for rapid detection of creatine kinase (CK-MM)

Creatine kinase, a key biomarker associated with many debilitating physiological conditions has seldom been detected in biological fluids using functionalized gold nanoparticles (GNPs). We have developed a method based on the aggregation of cysteamine (Cys) functionalized GNPs in presence of ATP for effective detection of creatine kinase (CK-MM). Positively charged Cys-GNPs (brick red color) aggregate in presence of negatively charged ATP (blue color) but the process is prevented when CK-MM is added to the solution. The analytical response to the concentration of CK-MM is linear (R2 = 0.9850). The proposed method is selective in sensing the CK-MM for a range of 5.617 × 103 ng/ml, 0.5617 ng/ml. The limit of detection was found to be 0.569 ng/ml in solution and 0.553 ng/ml in human serum with high selectivity.

Presenting Precision Glycomacromolecules on Gold Nanoparticles for Increased Lectin Binding.

Glyco-functionalized gold nanoparticles have great potential as biosensors and as inhibitors due to their increased binding to carbohydrate-recognizing receptors such as the lectins. Here we apply previously developed solid phase polymer synthesis to obtain a series of precision glycomacromolecules that allows for straightforward variation of their chemical structure as well as functionalization of gold nanoparticles by ligand exchange. A novel building block is introduced allowing for the change of spacer building blocks within the macromolecular scaffold going from an ethylene glycol unit to an aliphatic spacer. Furthermore, the valency and overall length of the glycomacromolecule is varied. All glyco-functionalized gold nanoparticles show high degree of functionalization along with high stability in buffer solution. Therefore, a series of measurements applying UV-Vis spectroscopy, dynamic light scattering (DLS) and surface plasmon resonance (SPR) were performed studying the aggregation behavior of the glyco-functionalized gold nanoparticles in presence of model lectin Concanavalin A. While the multivalent presentation of glycomacromolecules on gold nanoparticles (AuNPs) showed a strong increase in binding compared to the free ligands, we also observed an influence of the chemical structure of the ligand such as its valency or hydrophobicity on the resulting lectin interactions. The straightforward variation of the chemical structure of the precision glycomacromolecule thus gives access to tailor-made glyco-gold nanoparticles (glyco-AuNPs) and fine-tuning of their lectin binding properties.

Green synthesis of mixed metallic nanoparticles using room temperature self-assembly

Bimetallic nanoparticles of silver (Ag) and gold (Au) were synthesized at room temperature using Curcumin. Reduction process of silver and gold ions with different molar ratios leads to production of different nanostructures including alloys and core-shells. Produced nanoparticles were characterized simultaneously with FTIR, UV/vis. spectroscopy, transmission electron microscopy (TEM), and Energy-dispersive X-ray (EDAX). UV/vis. optical absorption spectra of as synthesized nanoparticles reveals presence of surface palsmon resonance (SPR) of both silver at (425 nm) and gold at (540 nm) with small shift and broadness of gold band after mixing with resucing and capping agent in natural extract which suggest presence of bimetallic nano structure (Au/Ag). FTIR and EDAX data approve the presence of bimetallic nano structure combined with curcumin extract. TEM micrographs shows that silver and gold can be synthesized separately in the form of nano particles using curcumin extract. Synthesis of gold nano particles in presence of silver effectively enhance and control formation of bi-metallic structure.

Visual assessment of parasitic burden in infected macrophage by plasmonic detection of leishmania specific marker RNA

Visceral leishmaniasis is a neglected tropical disease and may prove fatal if not diagnosed and treated early. The amastigotes of Leishmania donovani nest in the macrophage of human host and thus, determination of parasitic burden in the infected macrophages has been the most crucial step in diagnosis, dose determination and medical management of relapse cases of this fatal disease. Microscopic count following Giemsa staining and other morphological analysis are the classical ways vastly used in the resource stringent endemic areas. The current method introduced a high throughput, rapid, cheap, non-gel, non-PCR and nonculture based visual detection platform employing salt triggered aggregation of gold nanoparticle in presence of extracted total RNA from infected macrophages and leishmania specific oligo-nucleotide probe to determine the parasite burden in macrophages. Amastigote's small subunit ribosomal RNA (SSU rRNA, PMID 1565128) was used as the leishmania specific marker and its abundance in the total RNA extracts of infected macrophages were determined by this visual colorimetric assay.

Aggregation behaviour of gold nanoparticles in presence of chitosan

Chitosan (CS) is a biocompatible polysaccharide with positive charge that is widely used as a coating agent for negatively charged nanoparticles. However, the types of structures that emerge by combining CS and nanoparticles as well as their behaviour are still poorly understood. In this work, we characterize the nanocomposites formed by gold nanoparticles (AuNPs) and CS and study the influence of CS in the expected aggregation process that should experience those nanoparticles under the favourable conditions of low pH and high ionic strength. Thus, at the working CS concentration, we observe the existence of CS structures that quickly trap the AuNPs and avoid the formation of nanoparticle aggregates in environmental conditions that, otherwise, would lead to such an aggregation.

Synthesis of Gold Nanoparticles in Presence of Ionic Liquid [Bmin][CF3SO3] with Humic Acid under Microwave Irradiation and Its Application as a Nanocatalyst

Synthesis of Gold Nanoparticles in Presence of Ionic Liquid [Bmin][CF3SO3] with Humic Acid under Microwave Irradiation and Its Application as a Nanocatalyst

Selective Effect of Procaine, Tetracaine and Dibucaine on Gold Nanoparticles

An aqueous colloid dispersion of gold nanoparticles (AuNPs) was prepared by reduction of gold(III) chloride and its interaction with three local anesthetics (procaine, dibucaine or tetracaine) was investigated. Optical spectra reveal the modifications in the absorption band of nanoparticles related to their self assembly mediated by anesthetic molecules and depending on the progress in time of the aggregation process. TEM images show the features of the self assemblies formed by the association of gold nanoparticles in presence of anesthetics, and reveal marked differences in the behavior of the AuNPs against the three anesthetics. The main effect of various anesthetics can be described in terms of electrostatic forces between the negatively charged metal nanoparticles and anesthetic molecules, existing in their cationic form at the working pH. Then, the anesthetics functionalized nanoparticles trigger specific interactions to form different self assemblies through a selective combination of hydrophobic and hydrogen bonding interactions between the coated nanoparticles and anesthetics molecular species.

Synthesis of Gold Nanoparticles in Presence of Poly(vinyl pyrrolidone) from Gold Hydroxide Precursor Salt

Since the discovery, gold nanoparticles (GNPs) have been attracting scientific and research communities owing to their biocompatibility, excellent thermal conductivity, low cytotoxicity, ease of processability, and highly functionalization capability. In this report, we discuss synthesis of gold nanoparticles with poly(vinyl pyrrolidone) (PVP) in 1–butanol from gold hydroxide, a new precursor salt. An emergence of a strong surface plasmon absorption band at 535 nm confirms formation of GNPs in the colloidal solution. The stability of Au colloid was studied by using UV–Visible and zeta potential measurements. The interfacial interaction between GNP and PVP molecules was studied in terms of Fourier transform infrared and X–ray photoemission spectrum (XPS). Marked enhancement in some of the vibrational bands (e.g., C=O, C–H, and C–N stretching) of PVP molecules in presence of GNPs reveals existence of an interaction between this two major constituents. However a small red-shift in the C=O stretching frequency of pyrrolidone group of PVP molecule implies that a weak interaction occurs via O–atom of carbonyl group. Appearance of Au4f doublet band at 82.7 and 86.4 eV in XPS spectrum with a chemical shift of 3.7 eV further confirms formation of GNPs by reduction of Au3+ to Au0 chemical state in presence of PVP. A noticeable negative shift in the binding energies of Au4f doublet band as compared to bulk Au atom suggests an interfacial interaction between GNP and PVP molecules. Transmission electron microscopic images propose that Au crystalline core is covered by an amorphous layer of PVP molecules.

Gold nanoparticles-coated poly(3,4-ethylene-dioxythiophene) for the selective determination of sub-nano concentrations of dopamine in presence of sodium dodecyl sulfate

For the first time, a novel electrochemical sensor; gold nanoparticles-coated poly(3,4-ethylene-dioxythiophene) polymer modified gold electrode in presence of SDS (Au/PEDOT-Aunano…SDS) was developed by the electrodeposition of gold nanoparticles on poly(3,4-ethylene-dioxythiophene) (PEDOT) modified gold electrode for the selective determination of dopamine (DA) in presence of uric acid (UA) and ascorbic acid (AA) in presence of sodium dodecyl sulfate (SDS). Synergism between the composite of conducting polymer matrix and gold nanoparticles in presence of SDS for electron transfer enhancement of DA is explored. Electrochemical investigation and characterization of the modified electrode are achieved using cyclic voltammetry, electrochemical impedance spectroscopy, scanning electron, and atomic force microscopies. The oxidation current signal of DA is remarkably stable via repeated cycles and has unique long term stability. Very small peak potential separation (ΔEp), almost zero or 15mV is also obtained by repeated cycles indicating unusual high reversibility. The use of SDS in the electrochemical determination of DA using linear sweep voltammetry at Au/PEDOT-Aunano modified electrode resulted in determining DA at very low concentrations. The DA concentration could be measured in the linear range of 0.5–20μmolL−1 and 25–140μmolL−1 with correlation coefficients of 0.9978, and 0.9987, and detection limits of 0.39nmolL−1 and 1.55nmolL−1, respectively. The validity of using this method in the determination of DA in human urine was also demonstrated. It has been shown that modified electrode can be used as a sensor with high reproducibility, sensitivity, selectivity, and long term stability.

Synthesis of Core-Shell Gold Nanoparticles with Maltose-Modified Poly(Ethyleneimine)

The synthesis of ultrafine gold nanoparticles in presence of maltose-modified hyperbranched poly(ethyleneimines) (PEI) is described. The polymer acted as both a reducing and stabilising agent in the particle formation process. The nanoparticles were characterized by means of dynamic light scattering (DLS), transmission electron microscopy (TEM), analytical ultracentrifugation (AUC), small-angle x-ray scattering (SAXS), and small-angle neutron scattering (SANS). The mechanism of nanoparticle formation can be described in two steps. The reduction process of the Au3+ ions located in the inner coil region of the hyperbranched PEI led to the formation of a compact gold core, and is accompanied by a collapse of the polymer coil. Therefore, in the subsequent reduction process a gold-polymer hybrid shell is formed. By using the PEI of higher molar mass, core-shell gold nanoparticles of about 3.6 nm size with a more narrow size distribution and special fluorescence behavior could be synthesized.

Gold and gold–copper nanoparticles in 2-propanol: A radiation chemical study

The studies on the reduction of Au 3+ to gold nanoparticles in presence and absence of Cu 2+ under deoxygenated conditions in 2-propanol by radiolytic method have been carried out. On γ-radiolysis, preliminary yellow colored solution of Au 3+ changed to purple color owing to gold nanoparticles formation, which exhibits an absorption peak at around 540 nm. In the presence of Cu 2+, absorption of gold–copper nanoparticles, which was also produced during γ-radiolysis, was red shifted in contrast to the system containing no Cu 2+. Under DLS studies the sizes of gold nanoparticles in the absence and the presence of Cu 2+ were found to be larger (>400 nm). However, in presence of polyethylene glycol, a stabilizer the nanoparticle sizes became smaller, sizes measured for gold and gold–copper nanoparticles are 40 and 140 nm, respectively. Moreover, the change in UV–vis spectra in the Cu 2+ and Au 3+ mixed system highlights the formation of gold–copper nanoparticles in core–shell type arrangement.

An anisotropic snowflake-like structural assembly of polymer-capped gold nanoparticles

Snowflake-like structural assembly of isotropic gold nanoparticles (GNPs) is reported. A modified polyamine method has been employed to synthesize positively charged GNPs in presence of a polymeric metaphosphate. This process yields fascinating dendritic self-assembled morphologies. Structural characterization revealed that there was aggregation of crystalline GNPs. The aggregates of GNPs formed in the initial stage of synthesis are assumed to act as the bulging seeds for final growth of complex morphologies at nanometer to micrometer length scale. Self-assembly of GNPs was found to be greatly influenced by the concentration of gold precursor. Diffusion limited aggregation of GNPs is suggested as the plausible mechanism for this nanoparticle self-organization process.

Preparation of gold nanoparticles under presence of the diblock polyampholyte PMAA-b-PDMAEMA

The preparation of gold nanoparticles in presence of different weak polyampholytes is investigated. As diblock polyampholytes several poly(methacrylic acid)-block-poly((dimethylamino)ethyl methacrylate), PMAA-b-PDMAEMA, have been used, characterized by different molecular weight and block ratio. HAuCl4 is used as gold precursor where LiBH4 is acting as reductive agent to obtain the gold nanoparticles. The addition of gold precursors to aqueous solutions of PMAA-b-PDMAEMA polyampholytes leads to an acidification of the solution resulting in a change of the polyampholyte conformation through protonation of the PDMAEMA blocks. This modification of polyampholyte conformation also allows the tuning of the size and size distribution of the accordingly formed gold nanoparticles. Investigations presented, are performed mainly by AFM of the systems in thin film adsorbed on native oxide-terminated Si substrate. TEM was used to reveal the change in size of the obtained gold nanoparticles.

Protein seeding of gold nanoparticles and mechanism of glycation sensing

The plasmon resonance of gold nanoparticles (GNPs) synthesized on a protein template senses formation of advanced glycosylated end products (AGEs). A graded alteration of plasmon resonance (both the peak and intensity are affected) is observed as the glycation progresses. Transmission electron microscopy shows significant shift of the size distribution of GNPs in presence of glycation. The higher plasmon resonance is thus caused by increased formation of GNPs, which in turn is attributed to a larger number of smaller particles. To study the binding of the protein with the GNP, infrared (IR) spectroscopy and circular dichroism (CD) studies were undertaken. Whereas the CD studies confirmed the emergence of β-structure and loss of α-helix, the IR data indicated glycation-induced alterations in the amide I region. The proposed sensor for formation of AGEs thus apparently operates by direct or indirect conjugation with amino groups. Incidentally, glycation and AGE formation are responsible for a number of diabetes-related clinical conditions, and the present approach could be adopted for use for a simple colorimetric assay for the AGEs.

Photosynthesis of Gold Nanoparticles in Presence of Proteins

This paper describes the photosynthesis of gold nanoparticles (GNPs) in the presence of bovine serum albumin (BSA). The concentration of NaAuCl4 and the relative ratio of NaAuCl4 to BSA are important parameters for controlling the size of the GNPs. We prepared GNPs having average diameters ranging from 7 to 50 nm by illumination (Hg-Xe lamp) of phosphate-buffered solutions (pH 3.0-11.0) containing 1 mM NaAuCl4 and 10 microM BSA for 9 h. The size distribution of the GNPs synthesized at pH 7.0 is narrower relative to that of those prepared at other values of pH. Based on the observation that there are no GNPs formed at 25 degrees C in the absence of either BSA or illumination, we conclude that photolytic reduction is the main mechanism for the formation of the GNPs and that BSA acts as a capping agent to stabilize the as-synthesized GNPs. In addition to BSA, several other proteins, such as beta-casein, conalbumin, hemoglobin, beta-lactoglobulin, lysozyme, myoglobin, ovalbumin, pepsin, and trypsinogen play the same role.