Dissolution Of Gold Nanoparticles Research Articles

A microscopic view on the electrochemical deposition and dissolution of Au with scanning electrochemical cell microscopy – Part I

The nucleation and dissolution of gold nanoparticles (NPs) on a glassy carbon substrate have been studied with a local electrochemical approach based on Scanning Electrochemical Cell Microscopy (SECCM). By performing hundreds of locally-resolved voltammograms, a distribution of responses for nucleation was found when scanning multiple regions of the substrate, addressing experimentally the statistical nature of the nucleation and growth process at the micro-scale. Moreover, the confinement of the electrochemical cell to the SECCM meniscus enables us to resolve a diversity of events during the electrochemical dissolution of previously electrodeposited NPs, characterized as current spikes during the voltammetric scans. These current events do not manifest in the macro-scale due to the averaging of the electrochemical response over the large electrode area and reveal previously untapped information from the electrochemical nucleation, growth, and dissolution of supported metal nanoparticles. This approach opens up new opportunities for the rational design (electrodeposition) of functional nanostructured materials and the evaluation of their durability under electrochemical polarization (resistance to electrodissolution). The ability to study these considering the heterogeneous nature of the supports and the differences within nanomaterial ensembles is essential for applications in electrochemical conversion and storage.

Diversity Matters: Influence of Surface Heterogeneities in the Electrochemical Nucleation and Dissolution of Au Nanoparticles

The investigation of the nucleation and dissolution of gold nanoparticles on a glassy carbon substrate with Scanning Electrochemical Cell Microscopy (SECCM) combined with in-situ electrochemical TEM (EC-TEM) revealed the subtle influence of the local properties of the substrate on the electrochemical processes. Conducting hundreds of locally-resolved voltammograms at the micro-scale resulted in the observation of a diversity of responses for nucleation, allowing to address experimentally the statistical nature of the nucleation and growth process. Moreover, during the electrochemical dissolution of previously electrodeposited nanoparticles (NPs), the confinement conditions of the SECCM-cell allowed the resolution of a multitude of events characterized as current spikes. Such current events are not observable in the macro-scale since the electrochemical response over the large electrode area is the convolution of the activity all over the electrode surface. The EC-TEM experiments demonstrated that such current spikes were generated by the dissolution of individual NPs distributed over a time range. Combining SECCM and EC-TEM unmasked information previously not seen from the electrochemical nucleation, growth, and dissolution of supported metal nanoparticles [1]. This approach could accelerate the discovery of novel functional electrode materials by facilitating the rational design of protocols for electrodeposition of nanostructured materials and the evaluation of their stability under electrochemical conditions. The possibility to consider the heterogeneous nature of the supports and the differences within nanomaterial ensembles opens the opportunity to consider the diversity of electrochemical parameters as descriptors to understand and describe the relationships between activity, stability, and structure.[1] M. Bernal, D. Torres, S. Semsari, M. Čeh, K. Žužek Rožman, S. Šturm, J. Ustarroz, Diversity matters: Influence of surface heterogeneities in the electrochemical nucleation and dissolution of Au nanoparticles, under revision

Colorimetric and label free detection of gelatinase positive bacteria and gelatinase activity based on aggregation and dissolution of gold nanoparticles

A simple and sensitive method was developed for the detection of bacteria gelatinase activity based on their enzymatic hydrolysis effect on the surface plasmon resonance (SPR) of gelatin functionalized gold nanoparticles (Au@gelatin NPs) in bacteria supernatant. Characterization of synthesized NPs showed a very thin gelatin layer on the surface of about 20 nm AuNPs which modified the intrinsic SPR property of AuNPs. The extracted supernatants of applied bacteria were incubated with Au@gelatin NPs. Gelatinase activity of bacteria resulted in gradual gelatin shell removal and subsequent dissolution of bare AuNPs. The presence of inducer agents such as NaCl as the common ingredient in the bacterial medium led to the aggregation process of AuNPs and further bacterial activity resulted in AuNPs dissolution. AuNPs colloid solution color was changed from red to purple after addition of bacteria supernatants with gelatinase activity to the reaction. Also, the spectroscopic studies showed that the gelatinase activity of bacteria resulted in the gradual decrease of absorbance at 529 nm and subsequently led to extinction of SPR characteristics. So, the observed absorbance decrease in UV–Vis spectra at 529 nm was indicated as the gelatinase activity of applied bacteria. Different strains of gelatinase positive Bacillus strains were used as the real sample and their gelatinase activity was determined in the present study. Also, sensitivity analysis of the applied method was determined through this method and the obtained results showed Bacillus subtilis gelatinase activity in the linear range of 0–120 U/mL and detection limit of 0.5 U/mL. This method introduced label free, facile and sensitive assay of the bacterial gelatinase activity without any complicated instrument, affording convenience and simplicity.

High performance cyanide sensing with tunable limit of detection by stimuli-responsive gold nanoparticles modified with poly (N,N-dimethylaminoethyl methacrylate)

Detection of cyanide ion (CN−) and design of new sensors with high sensitivity and selectivity are interesting topics in recent developments. Cyanide ions lead to immediate dissolution of gold nanoparticles (AuNPs) and distinct color changes from red to transparent colorless solution. The presence of any material e.g. stabilizer may affect dissolution mechanism and hence sensing properties. Here, we represent a novel sensor (Au-PDA) based on the AuNPs coated with poly (N,N-dimethylaminoethyl methacrylate) (PDMAEMA) for the detection of CN− with tunable sensitivity. PDMAEMA bearing tertiary amine groups not only induced stimuli-responsivity to the prepared Au-PDA as the sensor, but also influenced the sensing performance like linear response range and limit of detection (LOD). The detection process with the increase in CN− concentration in wide range of pHs as well as high ionic strength of the medium was monitored by reduction of the localized surface plasmon resonance band of AuNPs at 530 nm. In the optimized condition, this sensing approach exhibited excellent selectivity in contrary to other anions and cations. The highest sensitivity was obtained in basic media (i.e. pH 9) with a LOD of 4.7 × 10−6 μM and two linear ranges from 10−5-10−3 μM and 0.04–320 μM. The tunable sensitivity could be considered as the strength point of such sensor with lowest LOD for detection of CN− and such a controlled stimuli-responsivity will open up a promising route toward adjustable detection of other chemicals.

A New Eye Dual-readout Method for MiRNA Detection based on Dissolution of Gold nanoparticles via LSPR by CdTe QDs Photoinduction

Breast cancer (BC) is the most frequent cancer that affects one in eight women worldwide. Recent advances in early cancer diagnosis anticipates more efficient treatment and prolong patient survival. MicroRNAs expression profiling plays a key role in diagnosis of cancer such as BC in early stages. For the first time we describe direct injection of hot electrons from plasmonic gold nanoparticles (AuNPs) to adsorbed water molecules with photoinduction of CdTe quantum dots (QDs) with emission wavelength at ~560 nm. As a result of hot electrons exiting from AuNPs with red color, gold cations (holes) are gradually discharged (AuNPs dissolution) leading to a colorless solution. Our group applied this phenomenon to propose a spectral method for miRNA recognition based on different responsive disaggregation and aggregation of CdTe QDs interacted with single strand DNA probes and DNA/RNA heteroduplex respectively resulting in a detection limit of 4.4 pM. This method has been applied also for the determination of miR-155 in the human breast carcinoma MCF-7 cells and normal human embryonic kidney cell line (HEK 293).

Smart phone assisted detection and quantification of cyanide in drinking water by paper based sensing platform

An organometallic dye, europium tetrakis dibenzoylmethide triethylammonium (EuD4TEA) and gold nanoparticles (Au NPs) impregnated paper based sensor platform have been utilized for development of fluorescence turn-on cyanide assay in aqueous media. The ordinary filter paper with 6μ m pore size were employed as solid support that facilitates impregnation of EuD4TEA and gold nanoparticles and provides durability. Detection mechanism relying on two processes (i) dissolution of gold nanoparticles causing fluorescence recovery and (ii) ligand exchange of triethyl amine with CN group stimulating cyanide specific fluorescence enhancement. The paper platform exhibit naked eye distinguishable color transition upon CN− addition from 10−2 to 10−12M. To standardize the methodology a homemade image processing algorithm has been developed that enabling calibration of color change and quantify CN− concentration. The described algorithm is applicable to Android smart phones and facilitate transforming these devices into a quantitative cyanide detector. The overall methodology provides instrument free cyanide detection and therefore rapid control of water quality and safety at off-field conditions.

Gold nanoparticles dissolution based colorimetric method for highly sensitive detection of organophosphate pesticides

A simple and sensitive colorimetric method is developed for organophosphrous pesticides (OPs) analysis based on the enzymatic hydrolysis reaction of acetylcholinesterase and the dissolution of gold nanoparticles (AuNPs) in Au3+-cetyltrimethylammonium bromide (Au3+-CTAB) solution. In the absence of OPs, the enzymatic hydrolysis product, thiocholine, would reduce Au3+ and protect the AuNPs from dissolution by the Au3+-CTAB. In the presence of OPs, however, the activity of AChE is inhibited, which could not or could only produce a small amount of thiocholine to consume the Au3+. In this case, the large amount of residual Au3+ dissolves the AuNPs and decreases both the concentration and size of the AuNPs, thus leading to an obvious red-to-light pink or red-to-colorless color change. Under optimal conditions, the colorimetric method could indicate the presence of OPs, with the concentration down to 0.7ppb. After loading AuNPs on a cellulose paper, an AuNPs-coated dipstick is developed for the detection of OPs, which is highly sensitive with an observable limit of detection of 35ppb. Practical sample analyses in tap water, apple washing solution, and sea water indicate the colorimetric method has acceptable accuracy and good stability, even in the system containing 5M of NaCl. Regarding these merits, the as-proposed method could be applied for the point-of-care analysis of OPs in complex systems.

Paper-Based Device for Rapid Visualization of NADH Based on Dissolution of Gold Nanoparticles.

We describe a paper-based device that enables rapid and sensitive room-temperature detection of dihydronicotinamide adenine dinucleotide (NADH) via a colorimetric readout and demonstrate its value for monitoring NAD+-driven enzymatic reactions. Our system is based on NADH-mediated inhibition of gold nanoparticle (AuNPs) dissolution in a Au3+-cetyltrimethylammonium bromide (CTAB) solution. We fabricated a device consisting of a mixed cellulose ester paper featuring a wax-encircled, AuNP-coated film atop a cotton absorbent layer sandwiched between two plastic cover layers. In the absence of NADH, the Au3+-CTAB complex dissolves the AuNP layer completely, generating a white color in the test zone. In the presence of NADH, Au3+ is rapidly reduced to Au+, greatly decreasing the dissolution of AuNPs and yielding a red color that becomes stronger at increasing concentrations of NADH. This device exploits capillary force-assisted vertical diffusion, allowing us to apply a 25 μL sample to a surface-confined test zone to achieve a detection limit of 12.5 μM NADH. We used the enzyme glucose dehydrogenase as a model to demonstrate that our paper-based device can monitor NAD+-driven biochemical processes with and without selective dehydrogenase inhibitors by naked-eye observation within 4 min at room temperature in a small sample volume. We believe that our paper-based device could offer a valuable and low-cost analytical tool for monitoring NAD+-associated enzymatic reactions and screening for dehydrogenase inhibitors in a variety of testing contexts.

Functionalized polyacetylenes with strong luminescence: “turn-on” fluorescent detection of cyanide based on the dissolution of gold nanoparticles and its application in real samples

By dissolution of Au NPs, new polyacetylene-functionalized Au NPs were successfully developed as “turn-on” fluorescent probes for the detection of cyanide sensitively and selectively. The lowest concentration to quantify cyanide ions could be down to 3.0 × 10−6 M, and other common anions including AcO−, Br−, C2O42−, Cl−, CO32−, F−, HCO3−, NO2−, NO3−, PO43−, S2O82−, SCN−, SO32−, SO42−, HPO42−, and P2O74− had almost no influence. Furthermore, several real water samples spiked with cyanide, including local groundwater, tap water, boiled water, and lake water, were analyzed with RSD values less than 4%, and the experimental results demonstrated that our developed sensing system worked well in the above water samples.

A Highly Sensitive and Selective Fluorescent Probe for Cyanide Based on the Dissolution of Gold Nanoparticles and Its Application in Real Samples

We report a simple fluorescence method for detection of cyanide sensitively and selectively based on the dissolution of polymer-coated gold nanoparticles by cyanide. The lowest concentration for quantification of cyanide ions was 3.0×10(-7) M, and other common anions nearly have no influence. Furthermore, several real water samples spiked with cyanide, including local groundwater, tap water, boiled water, and lake water, were analyzed, and the experimental results demonstrated that our sensing system worked well in the above water samples, with a good linear correlation.

Effect of dioctyl sulfide on the kinetics of oxidative dissolution of gold nanoparticles in triton N-42 reverse micelles

The effect of additions of hydrophobic dioctyl sulfide (L) on the kinetics of dissolution of gold nanoparticles in the interaction with a dispersed aqueous hydrochloric solution of H2O2 in Triton N-42 reverse micelles (decane was the dispersion medium) was studied spectrophotometrically. The process consists of a two-stage oxidation Au0 → AuCl2− → AuCl4− at the surface of gold particles; the first stage occurs in two ways: a spontaneous reaction and an autocatalytic reaction involving AuCl4− ions. With small additions of L (cL < cAu), only spontaneous oxidation of Au(0) to Au(I) takes place because Au(I) is completely bound in an inert complex AuLCl. When unbound L is exhausted, the newly formed AuLCl is accumulated in micellar shells, changes the properties of the medium inside the micelles, and affects the rate constant of the autocatalytic reaction, which increases with increasing cL. At high concentrations of L, the coagulation of particles occurs instead of their dissolution, because of the deterioration of the protective properties of micellar shells as a result of the ingression and accumulation of dioctyl sulfide molecules on account of selective adsorption on gold particles. The rate constants of all stages of dissolution and coagulation are determined.

Femtosecond pulse excitation of vibrational wave packets in chloroform: The effect of gold nanoparticles

Excitation of pure chloroform or a gold colloid in chloroform (average nanoparticle diameter of 2.5 nm) with 740-nm femtosecond pulses of 23-fs duration leads to oscillations in the differential absorption signal ΔA(λ, t) recorded using white-light continuum. The main oscillation modes for both systems are close to the chloroform Raman resonance frequencies of 260, 367, and 668 cm−1. However, marked narrowing and splitting of bands in the Fourier-transform spectra of oscillations are observed in the system of gold colloid in chloroform. The intensity of oscillations linearly increases with the pump pulse intensity in the cases of pure chloroform and the system of gold colloid in chloroform. Apparently, the principal mechanism of excitation of coherent packets in chloroform is femtosecond impulsive stimulated Raman scattering (ISRS). Dissolution of gold nanoparticles leads to a four- to sixfold enhancement of the Raman resonance signal of chloroform in the gold colloid as compared with pure chloroform. The increase in the intensity of Raman resonances is presumably due to amplification in the near field of gold nanoparticles.

Lead ion detection in turbid media by pulsed photoacoustic spectrometry based on dissolution of gold nanoparticles

In this paper, we present a pulsed photoacoustic configuration for the detection of lead ion in aqueous solution based on the dissolution of gold nanoparticle. The photoacoustic signal is generated by laser-induced nanobubble. This technique allows for a sensitive measurement of size changes of the gold nanoparticles in the presence of lead ions even in turbid samples. As a first step, the best gold nanoparticle size and concentration were determined. Using 1.25 nM of gold nanoparticle with a diameter of 11 nm containing 1 mM of 2-mercaptoethanol, a linear range from 1 nM to 2.5 μM and a limit of detection of 0.5 nM were obtained. Then, to study the response of our system to strong light scattering in the medium, the scattering coefficient of samples containing lead ions was incremented using spherical silica particles (diameter 500 nm). The results corroborate that the technique used in this work is almost insensitive to light scattering.

Reversible Formation and Dissolution of Gold Nanoparticles through Turning On and Off Sequences of UV Light

Reversible formation and dissolution of gold nanoparticles through turning on and off UV light was reported. Gold ions (Au(3+)) were reduced to monodispersed gold nanoparticles by UV irradiation from a mixture of comb-like poly(oxyethylene)s and a gold salt. The prepared gold nanoparticles dissolved to yield gold ions (Au(3+)) when the UV light was switched off. Such formation and dissolution could be repeated persistently by turning the UV light on and off repeatedly.

Kinetics of oxidative dissolution of gold nanoparticles in triton N-42 reversed micelles

The dissolution of gold nanoparticles as a result of a reaction with dispersed aqueous solution of Cl− and H2O2 solubilized in Triton N-42 reversed micelles (an oxyethylated surfactant) in n-decane was studied photocolorimetrically. An adequate description of the process kinetics is provided by the following autocatalytic scheme (in a Cl− + H2O2 excess): Au0 → Au+, Au0 + Aun+ → 2Au3+, n = 1 and 3. The reactions involve the formation and redox decomposition of intermediate complexes with the oxidizer on the surfaces of metallic particles. Dimensional factors associated with gold particles (the surface and reactivity of gold particles change during the process) and micelles (as nanoreactors) affect the process kinetics. The first effect is taken into account when data processing is performed in terms of the current number and effective charge density of surface gold atoms; therefore, it does not affect the observed rate constants kd1 and kd2. The second effect makes kd1 and kd2 dependent on the micelle size through changing the quality of the aqueous medium and the reactivity of the reaction components, mainly the activity of water and its hydration and adsorption abilities.

A novel chemiluminescent immunoassay for microcystin (MC) detection based on gold nanoparticles label and its application to MC analysis in aquatic environmental samples

A novel chemiluminescent immunoassay method based on gold nanoparticles was developed for the detection of microcystins (MCs). The immunoassay included three main steps: indirect competitive immunoreaction, oxidative dissolution of gold nanoparticles, and indirect determination for MCs with Au3+-catalysed luminol chemiluminesent system. The method has a wide working range (0.05–10 µg L−1, r 2 = 0.9914), the limit of detection was determined to be 0.024 µg L−1, which is much lower than the World Health Organization's proposed guidelines (1 µg L−1) for drinking-water. The proposed method was applied to MC analysis in natural water and fish tissue samples, and most results in the proposed method were in agreement with the conventional indirect competitive enzyme-linked immunosorbent assay method, which indicated that the new chemiluminescent immunoassay was sensitive, reliable, and suitable for MC analysis in natural water and fish tissue samples.

Swift heavy ion-induced dissolution of gold nanoparticles in silica matrix

Gold nanoparticles embedded in silica matrix were prepared by co-evaporation. After deposition, the samples were annealed at different temperatures in inert environment for 30 min. No signature of nanoparticle formation was found in case of as-deposited samples, while the annealed samples showed a clear signature of a surface plasmon resonance absorption peak around 520 nm, which indicated the formation of Au nanoparticles. The samples annealed at 900 °C were irradiated with 100 MeV Ag ions at fluences 2.5×1012 and 1×1013 ions/cm2. UV-visible absorption measurements of pristine and irradiated films showed a clear signature of dissolution of Au nanoparticles with ion beam fluence. X-ray diffraction studies of pristine and irradiated samples also supported the dissolution of Au nanoparticles with ion beam fluence. Rutherford backscattering spectrometry was used for quantification of gold.

Reaction Dynamics for Gold Nanoparticles Synthesis in Solution Plasma

ABSTRACTWe describe the dynamics of the synthesis of gold nanoparticles by glow discharge in aqueous solutions. Initial [AuCl4]− concentration and the voltage applied between the electrodes were varied. Reduction rates were calculated from changes in concentration of [AuCl4]− vs. discharge time. A pulsed power supply was used to generate discharges in the aqueous solutions. The morphology of the nanoparticles obtained was observed by transmission electron microscopy (TEM). [AuCl4]− was reduced by H radicals or electrons generated by the discharge. Dendrite-shaped nanoparticles ∼150 nm in size were formed after discharge for 1 min. The pH of the solution decreased gradually with increasing discharge time. The decrease in pH led to dissolution of gold nanoparticles. The reduction and dissolution rates increased proportionately with the applied voltage. The size of gold nanoparticles decreased during discharge and was 20 nm after discharge for 45 min. When the reduction rate lowered as a result of dissolution, anisotropic nanoparticles were formed and continued to grow in the solution.

A Novel Chemiluminescence Metalloimmunoassay Based on Gold Label

A novel chemiluminescence (CL) metalloimmunoassay based on the dissolution of gold nanoparticles has been presented as demonstrated by the determination of biotinylated antibody and IgG. The experimental conditions such as gold dissolution and CL reaction were optimized. In the detection format of primary antibody-IgG-antibody modified gold (10 nm and 30 nm gold), the dynamic range of IgG extended between 1–75 ng and 0.5–25 ng, respectively. The detection limit was estimated to be 0.5 ng for 10 nm of gold and 0.1 ng for 30 nm of gold. In the detection format of primary antibody-IgG-biotinylated antibody-streptavidin gold (5 nm and 10 nm), the dynamic range of IgG extended between 10–250 ng and 1–250 ng, respectively. The detection limit was estimated to be 5 ng for 5 nm of gold and 1 ng for 10 nm of gold. Overall, this novel method can be readily extended to a large variety of clinical bioaffinity assays of analysis and the detection of DNA hybridization.

Cylindrical conical gears with line contact. (in German) : I. Szekely, Rev. Roumaine Sci. Tech., Ser.Mecan. Appl., 10 (1) (1965) 217–228

An organometallic dye, europium tetrakis dibenzoylmethide triethylammonium (EuD4TEA) and gold nanoparticles (Au NPs) impregnated paper based sensor platform have been utilized for development of fluorescence turn-on cyanide assay in aqueous media. The ordinary filter paper with 6 μ m pore size were employed as solid support that facilitates impregnation of EuD4TEA and gold nanoparticles and provides durability. Detection mechanism relying on two processes (i) dissolution of gold nanoparticles causing fluorescence recovery and (ii) ligand exchange of triethyl amine with CN group stimulating cyanide specific fluorescence enhancement. The paper platform exhibit naked eye distinguishable color transition upon CN− addition from 10−2 to 10−12 M. To standardize the methodology a homemade image processing algorithm has been developed that enabling calibration of color change and quantify CN− concentration. The described algorithm is applicable to Android smart phones and facilitate transforming these devices into a quantitative cyanide detector. The overall methodology provides instrument free cyanide detection and therefore rapid control of water quality and safety at off-field conditions.