Incorporation Of AuNPs Research Articles

Characterization of Films of Weak Polyelectrolytes Incorporated with Poly(vinyl-pyrrolidone)-Stabilized Gold Nanoparticles

The incorporation process of gold nanoparticles (Au NPs) into self-assembled films was obtained using the layer-by-layer (LbL) technique where two weak polyelectrolytes, i.e., poly(allylamine hydrochloride) (PAH) as polycation and poly(acrylic acid) (PAA) as polyanion, were sequentially adsorbed. To evaluate this process, the films of PAH and PAA were immersed in gold solutions containing different sizes of Au NPs (6 nm and 10 nm) stabilized with poly(vinyl-pyrrolidone) (PVP) before and after treatment with a 0.1 mol L(-1) solution of hydrochloric acid. The systems were analyzed using a multi-method approach involving UV-Visible spectroscopy (UV-Vis), X-ray diffraction (XRD), atomic force (AFM) and transmission electron microscopy (TEM). The results showed that the self-assembled polyelectrolyte films that were not treated by acid showed greater incorporation and better distribution of Au NPs.

Effect of gold nanoparticles on the electrocatalytic reduction of oxygen by silica encapsulated cobalt phthalocyanine

Electrocatalysts based on mercaptopropyl functionalized mesoporous silica supported cobalt phthalocyanine (MPS-CoPc) are prepared by co-condensation of 3-mercaptopropyltriethoxysilane and tetraethyl orthosilicate in the presence of cetyltrimethylammonium bromide as a templating agent followed by incorporation of cobalt phthalocyanine (CoPc). Further, gold nanoparticles (Au NPs) are introduced into/onto the MPS-CoPc materials (i.e. Au-MPS-CoPc). Transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and UV–vis diffuse reflectance are employed to investigate structural and physical properties of catalysts. The electrocatalytic behavior of the above materials for dioxygen reduction is evaluated by cyclic voltammetry (CV). The CV results show that the MPS-CoPc and Au-MPS-CoPc modified electrodes are highly active towards the electrocatalytic oxygen reduction. With the incorporation of Au NPs, significant increase in current and considerable decrease in oxygen reduction potential is observed.

Surface Plasmon Resonance Biosensors Incorporating Gold Nanoparticles

SPR biosensing is increasingly popular for the detection of a multitude of biomolecules. It offers label-free detection and study of proteins, nucleic acids, and other biomolecules in real time. A recent trend involves incorporation of AuNPs, either within the sensing surface itself or as signal enhancing tagging molecules. The importance of AuNP and detecting agent spacing is described and techniques using macromolecular spacing aids are highlighted. Recent methods to enhance SPR detection capabilities using gold nanoparticles are reviewed, as well as device fabrication and the results of incorporation. SPR detection is a highly versatile method for the detection of biomolecules and, with the incorporation of AuNPs, shows promise in extending it to a number of new applications.

Synthesis of Gold Catalysts Supported on Mesoporous Silica Materials: Recent Developments

Mesoporous silica materials (MSM) with ordered and controllable porous structure, high surface area, pore volume and thermal stability are very suitable catalyst supports, because they provide high dispersion of metal nanoparticles and facilitate the access of the substrates to the active sites. Since the conventional wet-impregnation and deposition-precipitation methods are not appropriate for the incorporation of gold nanoparticles (AuNPs) into MSM, considerable efforts have been made to develop suitable methods to synthesize Au/MSM catalysts, because the incorporation of AuNPs into the channel system can prevent their agglomeration and leaching. In this review, we summarize the main methods to synthesize active gold catalysts supported on MSM. Examples and details of the preparative methods, as well as selected applications are provided. We expect this article to be interesting to researchers due to the wide variety of chemical reactions that can be catalyzed by gold supported catalysts.

Chitosan microparticles incorporating gold as an enhanced contrast flow tracer in dynamic X-ray imaging

In situ monitoring of a biofluid can provide important information on circulatory disorders and a basic understanding on the metabolic mechanisms of living organisms. X-ray imaging has significant advantages as one of the most popular diagnostic tools to seethrough various biological systems. Particle traced velocity field measurement is one of the most popular methods for quantitative analysis of dynamic flow motion. In this study we have developed chitosan microparticles incorporating gold nanoparticles (AuNP) as a new enhanced contrast flow tracer for dynamic X-ray imaging. Gold is a useful material possessing high X-ray absorption ability and also biocompatibility. We chose chitosan as an AuNP delivery system because it can effectively trap AuNPs at high yield. In particular, the unique gold ion reduction ability of and compatibility with surface-modified chitosans are effectively utilized. The physical properties of the Au–chitosan microparticles can be controlled by varying the molecular weight of the chitosan employed and the AuNP incorporation methodology. The environment of the particles and the type of applied X-ray essentially determine the imaging efficiency. The designed chitosan microparticles incorporating Au have been successfully applied to track the digestive mechanisms occurring in delicate insects such as live mosquitoes.

The Effect of Multilayer Gold Nanoparticles on the Electrochemical Response of Ammonium Ion Biosensor Based on Alanine Dehydrogenase Enzyme

The use of multilayer of gold nanoparticles (AuNPs) attached on gold electrode surface via thiol chemistry to fabricate an ammonium (NH4+) ion biosensor based on alanine dehydrogenase (AlaDH) was investigated. The approach of the study was based on construction of biosensor by direct deposition of AuNPs and 1,8-octanedithiol (C8-DT) onto the gold electrode surface. For the immobilisation of enzyme, 2-mercaptoethanol (2BME) was first covalently attached to AlaDH via esther bonding and then followed by chemically attached the 2BME-modified AlaDH (2BME-AlaDH) moiety onto the AuNPs electrode via the exposed thiol group of 2BME. The resulting biosensor response was examined by means of amperometry for the quantification ofNH4+ion. In the absence of enzyme attachment, the use of three layers of AuNPs was found to improve the electrochemistry of the gold electrode when compared with no AuNPs was coated. However, when more than three layers of AuNPs were coated, the electrode response deteriorated due to excessive deposition of C8-DT. When AlaDH was incoporated into the AuNPs modified electrode, a linear response toNH4+ion over the concentration range of 0.1–0.5 mM with a detection limit of 0.01 mM was obtained. In the absence of AuNPs, theNH4+ion biosensor did not exhibit any good linear response range although the current response was observed to be higher. This work demonstrated that the incorporation of AuNPs could lead to the detection of higherNH4+ion concentration without the need of dilution for highNH4+ion concentration samples with a rapid response time of <1 min.

New nanostructured electrochemical biosensors based on three-dimensional (3-mercaptopropyl)-trimethoxysilane network

The design and characterization of a new nanostructured organic-inorganic hybrid material and its application to L-lactic acid determination are described. This material is based on the integration of the enzyme lactate oxidase (LOx) and gold nanoparticles (AuNPs) into a sol-gel 3D polymeric network derived from (3-mercaptopropyl)-trimethoxysilane (MPTS) previously formed onto a gold surface. MPTS presents the advantage of forming a 3D polymeric network containing a large number of thiol tail groups distributed throughout its structure that enable both its anchoring onto gold surfaces and the AuNPs incorporation. Moreover, this matrix provides a biocompatible environment that preserves the catalytic activity of LOx after its immobilization and allows the incorporation of a high amount of enzyme, which is expected to improve the sensitivity of the final biosensing device. Characterization of the designed biosensing platform was performed using quartz crystal microbalance (QCM), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. From the conjunction of these techniques, information about (i) the kinetic of LOx adsorption process in real time, (ii) the amount of LOx incorporated into the network, and (iii) the morphological characteristics at the nanometre level of the designed biosensing material was obtained. This information is very useful on the development of successful biosensing devices. Finally, the response of the biosensor to L-lactic acid was evaluated. The biosensor responds linearly to L-lactic acid in the range of 50 µM to 0.25 mM, with a sensitivity of 3.4 µA mM(-1) and a detection limit of 4.0 µM.

Sensitive fluorescent detection of Staphylococcus aureus using nanogold linked CdTe nanocrystals as signal amplification labels

A sensitive fluorescent assay was developed for the detection of DNA specifically for Staphylococcus aureus. A sandwich-type detection system was fabricated by first immobilizing biotinylated capture DNA on avidin-modified wells of microplates, then hybridizing the capture DNA with one end of the target DNA, and then recognizing the other end of the target DNA with a signal probe labeled with CdTe nanocrystals and gold nanoparticles (Au-NPs) at the 3′- and 5′-terminus, respectively. Hybridization was monitored by measuring the fluorescent intensity of the assembly. The experimental results demonstrated that the incorporation of Au-NPs in this detection system can significantly enhance the sensitivity and the selectivity because a single Au-NP can be loaded with hundreds of signal DNA probe strands modified with CdTe nanocrystals. Under the optimized conditions, a detection limit of 10 fmol of DNA per L can be achieved and at least 50 colony forming units of Staph. aureus per mL of sample can be detected. The method was assessed by analyzing real samples, and it was validated by comparing it to an official standard method.

A Label‐Free Amperometric Immunosensor Based on Redox‐Active Ferrocene‐Branched Chitosan/Multiwalled Carbon Nanotubes Conductive Composite and Gold Nanoparticles

AbstractA novel immunosensor has been developed by self‐assembling Au NPs onto a ferrocene‐branched chitosan/multiwalled carbon nanotubes (CS‐Fc/MWCNTs) modified electrode for the sensitive determination of hepatitis B surface antigen (HBsAg). The formation of CS‐Fc effectively avoids the leakage of Fc and retains its electrochemical activity. Incorporation of MWCNTs and Au NPs into CS‐Fc further increases the electrochemical active Fc in the CS films and provides interactive sites for the immobilization of HBsAb. The morphologies and electrochemistry of the formed biofilm were investigated by using scanning electron microscopy and electrochemical techniques. The immunosensor exhibits a specific response to HBsAg in the range of 1.0–420 ng mL−1. Excellent analytical performance, fabrication reproducibility and operational stability of the proposed immunosensor indicated its promising application in clinical diagnostics.

GOLD NANOPARTICLE-INCORPORATED POLYELECTROLYTE MULTILAYER FOR SENSITIVE ELECTROCHEMICAL IMMUNOSENSING

Reported was a novel amperometric immunosensor based on layer-by-layer (LbL) assembled polyethylenimine/gold nanoparticles/poly (acrylic acid) (PEI/AuNPs/PAA) multilayer. The assembly process was in situ monitored by surface plasmon resonance (SPR) technique. Anti-goat IgG as a capture antibody was covalently immobilized on the outermost PAA layer of the multilayer to construct an immunosensor. A target protein, goat IgG was electrochemically detected with alkaline phosphatase-conjugated anti-goat IgG (ALP-anti-goat IgG) as a recognition antibody. Electrochemical investigations suggest that the incorporation of AuNPs facilitates the electron transfer between the underlying electrode and the redox species in solution, and thus enhances the electrochemical signals and in turn improves the immunosensing performance. A detection limit of 100 pg mL-1 with a dynamic range of five orders of magnitude was achieved. Due to the protein-friendly environment and the protein resistance of the polyelectrolyte multilayer, the resulting immunosensor demonstrates excellent storage stability, satisfying assay specificity.

Characterization of Au‐metal nanoparticle‐hybridized poly (3,4‐ethylenedioxythiophene) films for electrochromic devices

AbstractIn order to enhance the electrochromic properties of poly (3,4‐ethylenedioxythiophene) (PEDOT), Au/PEDOT nano‐hybrid thin films were prepared from a Au nanoparticle (Au NP), 3,4‐ethylenedioxythiophene (EDOT), iron p‐toluenesulfonate and imidazole mixture. The incorporation of Au NPs slightly affected the surface roughness of PEDOT films but had an important impact on the conjugation length and packing density of PEDOT due to the physical volume effect. An enhancement in the electrochromic properties of PEDOT was obtained, in particular, a 50% reduction in the switching speed of PEDOT with a blue shift of the maximum absorption peak in the ultra violet‐visible spectroscopic analysis.

Photo-initiated miniemulsion polymerization as a route to the synthesis of gold nanoparticle encapsulated latexes

We report the first use of photo-initiated miniemulsion polymerization for the synthesis of well defined poly(methyl methacrylate) (PMMA) latexes. Furthermore, the application of photo-initiation is employed to the incorporation of decanethiol-capped gold nanoparticles (AuNPs). The procedure provides a low temperature polymerization for an oil-in-water miniemulsion with temperatures not exceeding 40 °C and polymerization times of only one hour. Using these mild reaction conditions allows the use of miniemulsion polymerization for the encapsulation of temperature sensitive species within the latex. Furthermore, we demonstrate the applicability of this method for the incorporation of decanethiol-capped AuNPs. Particle size distribution and morphology was studied using dynamic light scattering (DLS), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). PMMA latexes ranged between 100 and 200 nm in diameter showing good particle size distribution and tendencies to form semi-ordered domains. We show that variations in surfactant, hydrophobe and initiator concentrations behave in the same manner as miniemulsions initiated through conventional thermal methods. TEM observations revealed that the latexes with encapsulated AuNPs displayed even distributions of AuNPs throughout the PMMA latex with no aggregation witnessed.

A two-step surface modification approach for Au and CdS NPs loaded mesoporous thin films and the greatly enhanced optical nonlinearity

A new two-step surface modification approach has been developed for the incorporation of both CdS and Au NPs into the pore channels of silica mesoporous thin films. The composite thin films were investigated by FTIR, UV-vis, XRD and SEM, the results confirmed that the semiconductor and metal NPs were successfully incorporated with uniform particle size and high dispersivity thanks to the confinement effect of mesoporous thin films. The nonlinear optical susceptibility was measured by the Z-scan technique. The synthesized multi-component nanoparticles embedded films demonstrated a greatly enhanced nonlinear optical property which can be mainly attributed to the energy transfer between CdS and Au.

Role of Capping Ligands on the Nanoparticles in the Modulation of Properties of a Hybrid Matrix of Nanoparticles in a 2D Film and in a Supramolecular Organogel

We incorporate various gold nanoparticles (AuNPs) capped with different ligands in two-dimensional films and three-dimensional aggregates derived from N-stearoyl-L-alanine and N-lauroyl-L-alanine, respectively. The assemblies of N-stearoyl-L-alanine afforded stable films at the air-water interface. More compact assemblies were formed upon incorporation of AuNPs in the air-water interface of N-stearoyl-L-alanine. We then examined the effects of incorporation of various AuNPs functionalized with different capping ligands in three-dimensional assemblies of N-lauroyl-L-alanine, a compound that formed a gel in hydrocarbons. The profound influence of nanoparticle incorporation into physical gels was evident from evaluation of various microscopic and bulk properties. The interaction of AuNPs with the gelator assembly was found to depend critically on the capping ligands protecting the Au surface of the gold nanoparticles. Transmission electron microscopy (TEM) showed a long-range directional assembly of certain AuNPs along the gel fibers. Scanning electron microscopy (SEM) images of the freeze-dried gels and nanocomposites indicate that the morphological transformation in the composite microstructures depends significantly on the capping agent of the nanoparticles. Differential scanning calorimetry (DSC) showed that gel formation from sol occurred at a lower temperature upon incorporation of AuNPs having capping ligands that were able to align and noncovalently interact with the gel fibers. Rheological studies indicate that the gel-nanoparticle composites exhibit significantly greater viscoelasticity compared to the native gel alone when the capping ligands are able to interact through interdigitation into the gelator assembly. Thus, it was possible to define a clear relationship between the materials and the molecular-level properties by means of manipulation of the information inscribed on the NP surface.

A sensitive, label free electrochemical aptasensor for ATP detection

A sensitive, label free electrochemical aptasensor for small molecular detection has been developed in this work based on gold nanoparticles (AuNPs) amplification. This aptasensor was fabricated as a tertiary hybrid DNA–AuNPs system, which involved the anchored DNA (ADNA) immobilized on gold electrode, reporter DNA (RDNA) tethered with AuNPs and target-responsive DNA (TRDNA) linking ADNA and RDNA. Electrochemical signal is derived from chronocoulometric interrogation of [Ru(NH 3) 6] 3+ (RuHex) that quantitatively binds to surface-confined DNA via electrostatic interaction. Using adenosine triphosphate (ATP) as a model analyte and ATP-binding aptamer as a model molecular reorganization element, the introduction of ATP triggers the structure switching of the TRDNA to form aptamer–ATP complex, which results in the dissociation of the RDNA capped AuNPs (RDNA–AuNPs) and release of abundant RuHex molecules trapped by RDNA–AuNPs. The incorporation of AuNPs in this strategy significantly enhances the sensitivity because of the amplification of electrochemical signal by the RDNA–AuNPs/RuHex system. Under optimized conditions, a wide linear dynamic range of 4 orders of magnitude (1 nM–10 μM) was reached with the minimum detectable concentration at sub-nanomolar level (0.2 nM). Those results demonstrate that our nanoparticles-based amplification strategy is feasible for ATP assay and presents a potential universal method for other small molecular aptasensors.

Adsorption of Carboxylate-Modified Gold Nanoparticles on an Octadecylamine Monolayer at the Air/Liquid Interface

Gold nanoparticles (Au NPs) were prepared and surface-modified by mercaptosuccinic acid (MSA) to render a surface with carboxylic acid groups (MSA-Au). Octadecylamine (ODA) was used as a template monolayer to adsorb the Au NPs dispersed in the subphase. The effect of MSA concentration on the incorporation of Au NPs on the ODA monolayer and the relevant behavior of the mixed monolayer were studied using the pressure-area (pi-A) isotherm and transmission electron microscopy (TEM) observations. The experimental results showed that the adsorbed density of Au NPs is low without the surface modification by MSA. When MSA was added into the Au NP-containing subphase, the incorporation amount of Au NPs increased with increasing MSA concentration up to approximately 1 x 10-5 M for the particle density of 1.3 x 1011 particles/mL. With a further increase in the MSA concentration, the adsorbed particle density decreases due to competitive adsorption between the free MSA molecules and the MSA-Au NPs. It is inferred that free MSA molecules adsorb more easily than the MSA-Au NPs on the ODA monolayer. Therefore, an excess amount of MSA present in the subphase is detrimental to the incorporation of gold particles. The study on the monolayer behavior also shows that the pi-A isotherm of the ODA monolayer shifts right when small amounts of Au NPs or free MSA molecules are incorporated. However, when larger amounts of particles are adsorbed at the air/liquid interface, a left shift of the pi-A isotherm appears, probably due to the adsorption of ODA molecules onto the particle surface and the transferring of the particles from beneath the ODA monolayer to the air/water interface. According to the present method, it is possible to prepare uniform particulate films of controlled densities by controlling the particle concentration in the subphase, the MSA concentration, and the surface pressure of a mixed monolayer.