Aqueous Gold Nanoparticles Research Articles

Capping agent-free aqueous gold nanoparticles generated by an environmentally friendly plasma-liquid method

This study investigates a simple approach for synthesizing gold nanoparticles (Au NPs) using atmospheric pressure plasma without the need for reducing agents, additives, or capping agents. The size, morphology, optical properties, and aggregation stability of the synthesized Au NPs were characterized using scanning electron microscopy, UV-vis spectroscopy, and zeta potential analysis. The UV-vis absorption spectra of the gold nanoparticles, obtained at various Au3+ concentrations and treatment durations with anode plasma discharge, were analyzed. The UV-vis spectra revealed a surface plasmon resonance absorption band between 530–600 nm, indicative of Au NP formation. Results demonstrated that the size of Au NPs can be tuned within the range of 30–75 nm by adjusting the gold salt precursor concentration from 0.3 to 2.5 mmol/L. It was found that plasma treatment for 3–10 minutes, at different Au3+ concentrations, resulted in the formation of Au NPs with varying sizes and morphologies. The study showed that particles with different shapes – spherical, hexagonal, and triangular – were formed depending on the initial concentration of Au3+. The plasma-chemically synthesized nanoparticles at an Au3+ concentration of 0.06 mmol/L were predominantly spherical and exhibited the highest stability (lasting 12–24 hours), with a zeta potential of –20 to –22 mV, compared to samples with Au3+ concentrations ranging from 0.3 to 2.5 mmol/L.

Hydrophobicity and FTIR absorbance spectroscopy of Polydimethylsiloxane (PDMS) films treated with aqueous gold nanoparticles (AuNP) solution

Polydimethylsiloxane (PDMS) thin films were treated with aqueous solutions of gold nanoparticles. Samples treated for 24, 48, and 72 h, including untreated PDMS film, were subjected to hydrophobicity test and FTIR absorbance spectroscopy. Hydrophobicity test involved measuring the contact angle of water droplets placed on top of the sample films. Contact angles were measured using Image J software. Treated samples showed significant hydrophobicity changes shown by the increasing value of measured contact angle from 71.3° for the untreated sample to 104.0° for the sample treated for 72 h. FTIR absorbance spectra of the treated sample showed peaks at 3374 cm−1, 3295 cm−1, 2096 cm−1 and 2031 cm−1 with the peak intensity values increasing with corresponding samples of increasing hours of treatment. With the presence of gold nanoparticles on the PDMS film confirmed, the gold nanoparticles may now be functionalized for biosensing and biotesting applications of liquid samples.

Quantification of nanoparticles' concentration inside polymer films using lock-in thermography.

Thin nanocomposite polymer films embedding various types of nanoparticles have been the target of abundant research to use them as sensors, smart coatings, or artificial skin. Their characterization is challenging and requires novel methods that can provide qualitative as well as quantitative information about their composition and the spatial distribution of nanoparticles. In this work, we show how lock-in thermography (LIT) can be used to quantify the concentration of gold nanoparticles embedded in polyvinyl alcohol (PVA) films. LIT is an emerging and non-destructive technique that measures the thermal signature produced by an absorbing sample illuminated by modulated light with a defined frequency. Films with various concentrations of gold nanoparticles of two different sizes have been prepared by evaporation from homogeneous aqueous PVA gold nanoparticle suspensions. When the thin films were illuminated with monochromatic light at a wavelength close to the plasmonic resonance signature of the nanoparticles, the amplitude of the thermal signature emitted by the nanoparticles was recorded. The measurements have been repeated for multiple modulation frequencies of the incident radiation. We have developed a mathematical method to quantitatively relate the concentration of nanoparticles to the measured amplitude. A discussion about the conditions under which the sample thickness can be determined is provided. Furthermore, our results show how LIT measurements can easily detect the presence of concentration gradients in samples and how the model allows the measured signal to be related to the respective concentrations. This work demonstrates the successful use of LIT as a reliable and non-destructive method to quantify nanoparticle concentrations.

Formulation and characterization of a novel anti-human endometrial cancer supplement by gold nanoparticles green-synthesized using Spinacia oleracea L. Leaf aqueous extract

Gold nanoparticles as one of the productions of the chemistry field have a special place in the cure of many diseases. Many experiences in medicinal researches have indicated that the plants enhance the anticancer effects of gold nanoparticles. According to the above contents, we investigated the capacities of Spinacia oleracea L. leaf aqueous extract green-mediated gold nanoparticles (AuNPs) as a modern chemotherapeutic material in treating endometrial cancer. The physicochemical characterization tests including UV–Visible Spectroscopy (UV–Vis), Field Emission Scanning Electron Microscopy (FE‐SEM), Fourier Transformed Infrared Spectroscopy (FT‐IR), and Transmission Electron Microscopy (TEM) were used for investigating the physicochemical properties of AuNPs. To survey the antioxidant potentials of AuNPs, one of the common antioxidant techniques i.e., DPPH was used. Determination of anti-endometrial cancer effects of AuNPs was carried out by the MTT assay and against Ishikawa, KLE, HEC-1-A, and HEC-1-B cell lines. The physicochemical characterization analyses revealed that the AuNPs had been formulated as the best possible. The results of the DPPH test confirmed excellent antioxidant properties of AuNPs in comparison to the butylated hydroxytoluene. The AuNPs IC50 was 194 µg/mL in the antioxidant test. The results of the MTT assay confirmed removing Ishikawa, KLE, HEC-1-A, and HEC-1-B cell lines after treating with low concentrations of AuNPs. The IC50 of the AuNPs was 341, 335, 316, and 325 µg/mL against Ishikawa, KLE, HEC-1-A, and HEC-1-B cell lines, respectively. The best finding of anti-endometrial cancer potentials was determined in the HEC-1-A cell line. According to the above results, significant anti-endometrial cancer effects of Au nanoparticles green-mediated by S. oleracea leaf extract are confirmed. It is offered that the studies of the clinical trial are performed for approving the above findings in humans.

Cytotoxicity, anti-acute leukemia, and antioxidant properties of gold nanoparticles green-synthesized using Cannabis sativa L leaf aqueous extract

Metallic nanoparticles, especially gold nanoparticles, are used in the therapy of various diseases. Recently, many chemotherapeutic supplements or drugs have been formulated with gold nanoparticles. One option for synthesizing gold nanoparticles is to use herbs. Many previous studies have shown that medicinal herbs increase the antioxidant and cytotoxicity properties of gold nanoparticles against tumor cell lines. In this study, gold nanoparticles were prepared and synthesized in an aqueous medium using Cannabis sativa L leaf extract as stabilizing and reducing agents. In addition, we evaluated the anti-leukemia effects of gold nanoparticles against acute T-cell leukemia and lymphoblastic leukemia cell lines. Characterization of gold nanoparticles was done with FE - SEM, FT - IR, UV–Vis and TEM. The MTT test is used for anti-HAuCl4, C. sativa and C. Acute leukemia effects of AuNPs. To investigate the antioxidant potentials of HAuCl4, C. sativa aqueous extract and gold nanoparticles, the DPPH test was used in the presence of butylated hydroxytoluene as control. In UV–Vis, the clear peak at 538 nm wavelength showed the formation of gold nanoparticles. In the FT-IR, many antioxidant molecules with relevant bonds led to the perfect condition for gold reduction in gold nanoparticles. In addition, in TEM and FE-SEM images, gold nanoparticles were spherical, with an average size of 18.6 nm. The IC50 of gold nanoparticles were 329, 381, 275 and 218 µg / mL against MOLT-3, TALL-104, J.RT3-T3.5 and Clone E6-1 cell lines, and Jurkat, respectively. The best results of the anti-acute leukemia properties of gold nanoparticles were obtained in the Clone E6-1 cell line. Gold nanoparticles inhibited half of the DPPH at a concentration of 196 µg/mL. The above results confirm the excellent roles of the gold nanoparticles as new chemotherapeutic drugs in treating various types of acute leukemia.

Green synthesis, characterization, cytotoxicity, antioxidant, and anti-human ovarian cancer activities of Curcumae kwangsiensis leaf aqueous extract green-synthesized gold nanoparticles

The present work indicated the green synthesis, characterization, cytotoxicity, antioxidant, and anti-human ovarian cancer activities of gold nanoparticles containing Curcumae Kwangsiensis Folium (Leaf) aqueous extract. Characterization of gold nanoparticles was done by Field Emission Scanning Electron Microscopy (FE‐SEM), Transmission Electron Microscopy (TEM), Fourier Transformed Infrared Spectroscopy (FT‐IR), and UV–Visible Spectroscopy (UV–Vis). MTT assay was used on common ovarian cancer cell lines i.e., SW-626, PA-1, and SK-OV-3 to survey the cytotoxicity and anti-ovarian cancer effects of gold chloride, Curcumae Kwangsiensis Folium leaf aqueous extract, and gold nanoparticles. The best results of cytotoxicity and anti-ovarian cancer properties were seen in the case of gold nanoparticles. They had very low cell viability and high anti-ovarian cancer activities dose-dependently against PA-1, SW-626, and SK-OV-3 cell lines without any cytotoxicity on the normal cell line (HUVEC). For investigating the antioxidant properties of gold chloride, Curcumae Kwangsiensis Folium leaf aqueous extract, and gold nanoparticles, the DPPH test was used in the presence of butylated hydroxytoluene as the positive control. The best results of antioxidant properties were seen in the case of gold nanoparticles. They inhibited half of the DPPH molecules in the concentration of 153 µg/mL. Maybe significant anti-human ovarian cancer potentials of gold nanoparticles synthesized by Curcumae Kwangsiensis Folium leaf aqueous extract against common human ovarian cancer cell lines are linked to their antioxidant activities.

Toward Smaller Aqueous-Phase Plasmonic Gold Nanoparticles: High-Stability Thiolate-Protected ∼4.5 nm Cores.

Most applications of aqueous plasmonic gold nanoparticles benefit from control of the core size and shape, control of the nature of the ligand shell, and a simple and widely applicable preparation method. Surface functionalization of such nanoparticles is readily achievable but is restricted to water-soluble ligands. Here we have obtained highly monodisperse and stable smaller aqueous gold nanoparticles (core diameter ∼4.5 nm), prepared from citrate-tannate precursors via ligand exchange with each of three distinct thiolates: 11-mercaptoundecanoic acid, α-R-lipoic acid, and para-mercaptobenzoic acid. These are characterized by UV-vis spectroscopy for plasmonic properties; Fourier transform infrared (FTIR) spectroscopy for ligand-exchange confirmation; X-ray diffractometry for structural analysis; and high-resolution transmission electron microscopy for structure and size determination. Chemical reduction induces a blueshift, maximally +0.02 eV, in the localized surface plasmon resonance band; this is interpreted as an electronic (-) charging of the monolayer-protected cluster (MPC) gold core, corresponding to a -0.5 V change in electrochemical potential.

Measurement and multilayer model of cooling of gold nanoparticles: Transient thermoreflectance experiments and multilayer analytical modeling

We derive an analytical model of diffusive thermal transport in multilayer structures of spherical symmetry and apply it to transient thermoreflectance measurements of gold nanoparticles embedded in a polymer matrix. This multilayer approach significantly improves the quantitative measurement of material thermal properties, in comparison with single-layer methods. The model adapts the typical planar transfer matrix model to a spherical geometry, and we apply it to transient thermoreflectance (TTR) experiments on gold nanoparticles embedded in a polymer matrix, to published TTR data for aqueous platinum nanoparticles, and also to example systems of aqueous gold and platinum nanoparticles. We measure a thermal boundary conductance value of 410MW/m2K at the nanoparticle gold/polymer interface. The sensitivity of the TTR signal to system thermal properties is predicted as a function of the particle/matrix thermal boundary resistance (TBR), and we discuss the differentiation of TBR and capping layer effects on a TTR signal.

Aqueous Gold Nanoparticle Solutions for Improved Efficiency in Electrogenerated Chemiluminescent Reactions

The efficiency of the high-energy electrogenerated chemiluminescence (ECL) tris(2,2′-bipyridine)ruthenium(II)/oxalate reaction was determined in the presence of citrate-coated gold nanoparticle (AuNPs) aqueous solutions. The ECL efficiency (ΦECL) for this reaction is enhanced by the addition of increasing amounts of AuNPs, followed by a sharp decrease when [AuNPs] is higher than 1.6 × 10–8 M. To explain this ΦECL/[AuNPs] trend, photoluminescent (PL) quenching, transmission electronic microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS) measurements were also performed as well as redox potentials for the [Ru(bpy)3]3+/2+ couple. Two facts were noteworthy: First, there is an increase in ΦECL, which accompanies an energy transfer effect by coupling between the Ru(II) complex ECL emission band and the AuNPs surface plasmon resonance (SPR)-induced band. This coupling, which we have called the ECL-SPR effect, enabled the quantifying of a coefficient (KECL-SPR, ECL-SPR effectiveness) for the improved ...

Highly extended filaments in aqueous gold nano-particle colloidals

A new regime of filamentation has been discovered in aqueous gold nanoparticle colloidals (AGNC). Different from filamentation in liquids, in this regime, by doping water with gold nanoparticles, there is no observable multiple small-scale filaments, but instead a spatially continuous plasma channel is formed. The length of the filament is more than ten times as compared with that in water. Filamentation in AGNC is characterized by a colorful light channel, with generated supercontinuum ranging from 400 nm to 650 nm which is scattered along a cyan-orange path.

Controlled Microwave-Hydrolyzed Starch as a Stabilizer for Green Formulation of Aqueous Gold Nanoparticle Ink for Flexible Printed Electronics

Gold electrodes are important in some devices and certain applications where an inert, highly conductive feature is required. An aqueous gold nanoparticle (AuNP) ink suitable for inkjet printing was synthesized and formulated using starch and microwave-assisted heating. By varying the hydrolysis conditions of starch, the size, yield, and stability of the AuNP suspension can be controlled and optimized to achieve a jettable ink. The optimized formulation has a very low starch loading of only 1.75 wt % relative to gold, forming a highly stable AuNP ink, which upon drying already forms a very conductive film and sinters at low temperature. The overall synthesis protocol thus provides a greener and cheaper alternative to other AuNP synthesis methods. The sintering behavior of the film was monitored, wherein, upon heating, starch is degraded, crystallite growth increased, and the morphology changed from individual nanoparticles to a network of fused particles. The film sheet resistance decreased concomitant wi...

A Bifunctional Spin Label for Ligand Recognition on Surfaces.

In situ monitoring of biomolecular recognition, especially at surfaces, still presents a significant technical challenge. Electron paramagnetic resonance (EPR) of biomolecules spin‐labeled with nitroxides can offer uniquely sensitive and selective insights into these processes, but new spin‐labeling strategies are needed. The synthesis and study of a bromoacrylaldehyde spin label (BASL), which features two attachment points with orthogonal reactivity is reported. The first examples of mannose and biotin ligands coupled to aqueous carboxy‐functionalized gold nanoparticles through a spin label are presented. EPR spectra were obtained for the spin‐labeled ligands both free in solution and attached to nanoparticles. The labels were recognized by the mannose‐binding lectin, Con A, and the biotin‐binding protein avidin‐peroxidase. Binding gave quantifiable changes in the EPR spectra from which binding profiles could be obtained that reflect the strength of binding in each case.

Optical Detection of Nanoaggregates in highly Concentrated strongly Absorbing Colloids without Sample Dilution

The ability to monitor the flocculation, aggregation and settling of micro and nano-sized particles is important for many environmental, chemical, biological and biomedical processes. However, standard approaches such as dynamic light scattering or absorption spectroscopy require sample dilution for characterization of highly concentrated samples. In this model study a new method using total internal reflection (TIR) is demonstrated to directly detect aggregates in highly-concentrated, strongly-absorbing samples of aqueous gold nanoparticles without sample dilution or pretreatment. Aggregation of the gold nanoparticles is induced by changing solution pH or by increasing ionic strength. Results obtained using the new sensor with no dilution agree with the post-dilution results obtained by absorption spectroscopy, dynamic light scattering, and zeta potential measurements. This validation of the sensor by standard methodologies is important because earlier work with sensitive detection of aggregates in non-absorbing polystyrene nanoparticles precluded the use of standard methodologies.

A new fullerene-C60 – Nanogold composite for non-enzymatic glucose sensing

A new functionalized fullerene C60 – thiol capped gold nanoparticle based nanocomposite using 3-amino-5-mercapto-1,2,4-triazole as the ligand was designed and synthesized following electronic structure calculation via DFT formalism. The electrostatic potential map from the DFT optimized geometry implied C60 core of the composite to remain electron deficient, and a much reduced HOMO-LUMO energy gap for the composite towards enhanced electron-transport ability was noted. Experimentally, first, fullerene-C60 was functionalized with the multipolar group containing ligand 3-amino-5-mercapto-1,2,4-triazole, making it hydrophilic and its aqueous dispersion was subsequently used to make a composite with in-situ prepared aqueous phase gold nanoparticles. The composite modified glassy carbon electrode showed electrocatalytic behaviour towards sensing of glucose, studied via cyclic voltammetry and electrochemical impedance spectroscopy. Thus, the highly stable and low onset potential non-enzymatic sensor exhibited high electro-catalytic activity and effective electron transfer from the electro-catalyst to the substrate electrode in a linear concentration range spanning over 0.025–0.8mM and a higher sensitivity response of 1.2μAmM−1cm−2 with good reproducibility, long term stability, anti-interference ability and chloride poisoning resistance.

Fluorescent Indicator Displacement Assay: Ultrasensitive Detection of Glutathione and Selective Cancer Cell Imaging.

This Research Article reports the development of nanohybrid comprising of anionic carbon dots (ACD) protected gold nanoparticle (GNP). ACD directly cap GNP through its anionic surface functionalization leading to the formation of stable aqueous GNP dispersion. This newly developed ACD-GNP nanohybrid has been thoroughly characterized by different spectroscopic and microscopic techniques. This nanohybrid is successfully employed toward the selective sensing of glutathione (GSH). The mechanism of GSH sensing by this nanosensor is based on the GSH triggered displacement of fluorescent indicator ACD from the GNP surface. Upon capping GNP, intrinsic fluorescence of ACD gets quenched. Addition of GSH displaces the fluorescent indicator ACD from GNP surface and restores the fluorescence signal of ACD. This nanosensor exhibits very high selectivity as well as sensitivity toward glutathione over the other biothiols and can detect as low as 6 nM of GSH. More importantly, selective imaging of the cancer cells over the noncancerous cells was achieved by this ACD-GNP hybrid implying its potential applications in biosensing, as well as in cancer diagnosis.

Synthesis of Gold Nanoparticles and Association of DNA-Gold Nanoparticles

<p>This study examined the synthesis of gold nanoparticles using a non-ionic surfactant, polysorbate 80, and KAuCl<sub>4 </sub>in water. The gold nanoparticles, which were well dispersed in water, were analyzed by UV-vis spectroscopy and transmission electron microscopy (TEM). In addition, the SRY(sex-determining region Y) gene of the Bos taurus specific primer was designed, and this primer solution was mixed with the aqueous gold nanoparticles solution. The binding ability of DNA and gold nanoparticles was identified by polyacryllamide gel electrophoresis. The products of DNA linked with gold nanoparticles were also characterized by UV-vis spectroscopy and TEM.</p>

Fast Assembly of Gold Nanoparticles in Large-Area 2D Nanogrids Using a One-Step, Near-Infrared Radiation-Assisted Evaporation Process.

When fabricating photonic crystals from suspensions in volatile liquids using the horizontal deposition method, the conventional approach is to evaporate slowly to increase the time for particles to settle in an ordered, periodic close-packed structure. Here, we show that the greatest ordering of 10 nm aqueous gold nanoparticles (AuNPs) in a template of larger spherical polymer particles (mean diameter of 338 nm) is achieved with very fast water evaporation rates obtained with near-infrared radiative heating. Fabrication of arrays over areas of a few cm(2) takes only 7 min. The assembly process requires that the evaporation rate is fast relative to the particles' Brownian diffusion. Then a two-dimensional colloidal crystal forms at the falling surface, which acts as a sieve through which the AuNPs pass, according to our Langevin dynamics computer simulations. With sufficiently fast evaporation rates, we create a hybrid structure consisting of a two-dimensional AuNP nanoarray (or "nanogrid") on top of a three-dimensional polymer opal. The process is simple, fast, and one-step. The interplay between the optical response of the plasmonic Au nanoarray and the microstructuring of the photonic opal results in unusual optical spectra with two extinction peaks, which are analyzed via finite-difference time-domain method simulations. Comparison between experimental and modeling results reveals a strong interplay of plasmonic modes and collective photonic effects, including the formation of a high-order stopband and slow-light-enhanced plasmonic absorption. The structures, and hence their optical signatures, are tuned by adjusting the evaporation rate via the infrared power density.

Laser-driven phase transitions in aqueous colloidal gold nanoparticles under high pressure: picosecond pump-probe study.

Pump-probe transient extinction spectroscopy was used to analyze 355 nm picosecond laser heating-induced phenomena in 60 nm-diameter aqueous gold nanoparticles (AuNPs) under a high pressure of 60 MPa. Kinetic spectroscopy revealed that a supercritical layer surrounding the AuNP nucleated with a lifetime of approximately 1 ns during its dynamic expansion and decay for a fluence of 19.6 mJ cm(-2). Moreover, in the post-mortem transmission electron micrographs we observed a number of fragments, a small percentage of size-reduced cores, and erupted particles among the intact particles after 60 shots, suggesting that evaporation occurred under laser illumination. The particle temperature calculation indicated that evaporation begins with a liquid droplet AuNP surrounded by a supercritical layer at temperatures below the boiling point of gold. By applying high pressure, we obtained a clear picture of the evaporation event, which was not possible at ambient pressure because bubble formation caused particle temperatures to rise uncontrollably. In this study, we shed light on the critical role of the supercritical layer formed around the AuNP under high pressure during laser-induced evaporation.

Fluorescence Determination of L-Cysteine in Wound Dressings by Fluoroscein Coated Gold Nanoparticles

ABSTRACTA new method for the fluorimetric determination of L-cysteine in wound care dressings is reported using coated fluorescein gold nanoparticles. The procedure was performed with a continuous flow manifold to automate the process to improve the precision. Aqueous gold nanoparticles (size: 10.5 ± 1.2 nm) that were noncovalently adsorbed to fluorescein were employed for the determination of L-cysteine. The fluorescence of the fluorescein-gold nanoparticle compound was lower than the fluorescein fluorescence and increased in the presence of L-cysteine due to fluorescence resonance energy transfer. The fluorescence of the solution containing the fluorescein-gold nanoparticles was enhanced by a factor of 7.5 following the addition of L-cysteine. This effect was not observed when other amino acids were introduced. This fluorescence enhancement was used for the determination of L-cysteine. Good linearity was observed from 0.8 to 4.1 µM of L-cysteine, and the detection limit was 0.1 µM. The method was successfully employed to determine L-cysteine in wound care dressings.

Molecular Dynamics Simulations Using a Capacitance–Polarizability Force Field

We present molecular dynamics (MD) simulations using a capacitance–polarizability force field. This force field allows an atomistic description of charge migration within a particle and hence the image charge effects at the interface of such a particle. By employing atomic capacitance and polarizability as the key parameters that describe fluctuating charges and dipoles, we can thus explore the effect of charge migration on the structural dynamics. We illustrate the method by exploring gold nanoparticles in aqueous solutions and compare with previous simulation work. We reach the conclusion that the capacitance–polarizability force field MD method serves as a promising tool for simulating gold–water systems, indicating probable extensions to other metal solutions and for studies of more complicated systems provided that a proper parametrization of the capacitance force field can be made. For the particular system studied, it is found that the water molecules interact with the surface through oxygen atoms, leading to more hydrogen-bond donors than acceptors at the gold–water interface. A prominent shoulder peak is found in the radial distribution of oxygen atoms with respect to the gold surface, due to the fact that the oxygen atoms adsorbed at the on-top sites of the gold nanoparticle. The surface of the aqueous gold nanoparticle carries negative charge, which is balanced by the positive charge in the second outermost layer.