Dispersed Gold Nanoparticles Research Articles

Thermodynamic and spectroscopic characterization of a weakly polar liquid crystalline compound dispersed with polyvinyl pyrrolidone capped gold nanoparticles

In the present study a deliberate attempt has been made to examine the consequences of dispersion of gold nanoparticles in an azoxybenzene-based nematic liquid crystal, namely 4,4′- di pentyl azoxy benzene. Investigations were made on gold nanoparticles doped nematic liquid crystals analysing differential scanning calorimetry, polarized light microscopy, ultraviolet–visible absorption spectroscopy, photoluminescence and Fourier-transform infrared spectroscopy (FTIR). Gold nanoparticles of different concentrations 0.25, 0.5, and 1.0 wt% were dispersed in pure 4,4′- di pentyl azoxy benzene, and it was observed in the experiment that no significant change occurs in the crystal to nematic phase (Cr-Ne) transition temperature with the increase in gold nanoparticles concentration. However, the nematic to isotropic (Ne-Iso) transition temperature decreases significantly with the increase in gold nanoparticles concentration. This study reports around 76% increase in ultraviolet–visible absorbance and 46% enhancement of photoluminescence intensity with the suitable amount of gold nanoparticles dispersion in 4,4′- di pentyl azoxy benzene. The surface plasmonic resonance (SPR) and re-excitation of 4,4′- di pentyl azoxy benzene molecule due to collision with gold nanoparticles has been accredited to the escalation in photoluminescence intensities.

Measurement of thermal diffusivity of gold nanofluid according to particle size and temperature

The thermal diffusivity of a gold nanofluid containing 20, 40, or 80 nm particles prepared by dispersing gold nanoparticles in ethylene glycol was measured from room temperature to 80°C using the thermal lens effect in dual laser beam mode consisting of an excitation laser (532 nm) and a probe laser (633 nm). Three samples with three different nanoparticle sizes were prepared at the same concentration (3 × 10-5 wt.%). The thermal diffusivity was 1.020 × 10-7 m2/s (20 nm), 1.379 × 10-7 m2/s (40 nm), and 2.126 × 10-7 m2/s (80 nm) at RT, and 1.211 × 10-7 m2/s (20 nm), 1.784 × 10-7 m2/s (40 nm), and 2.758 × 10-7 m2/s (80 nm) at 80°C. Overall, the thermal diffusivity of a gold nanofluid was proportional to the nanoparticle size and increased with increasing temperature.

Functionalization of Gold Nanoparticles with Monosaccharide Mannose

Gold nanoparticles have found a wide range of application in biomedical sciences. Unique properties of these metal nanoparticles include surface plasmon resonance and size dependent colour change. Various molecules have been functionalized on the gold nanoparticles surface but carbohydrates have garnered attention due to their properties and their role in living systems. However certain challenges make carbohydrate-gold nanoparticles association difficult to obtain and stabilize. This study was carried out to chemically remodel gold nanoparticles by adding a monosaccharide mannose to its surface. A modified phase transfer method was used to synthesize gold nanoparticles. The surface of the nanoparticles was fixed with cyanuric chloride to serve as a linker. Mannose was then linked to the linker molecule. All three stages of the process, gold nanoparticles, and gold nanoparticles with linker and gold nanoparticles with the carbohydrate were analyzed for size and stability. Zeta potential and UV-vis data exhibited stable gold nanoparticles dispersion, successful binding of linker molecule as well as the carbohydrate. This study shows a simple, cost-effective and robust method of glycomodification of gold nanoparticles surface which can further find use in wide ranging applications.

Boosting electrocatalytic selectivity in carbon dioxide reduction: The fundamental role of dispersing gold nanoparticles on silicon nanowires

Carbon dioxide electrochemical reduction (CO2RR) has been recognized as an efficient way to mitigate CO2 emissions and alleviate the pressure on global warming and associated environmental consequences. Gold (Au) is reported as stable and active electrocatalysts to convert CO2 to CO at low overpotential due to its moderate adsorption strength of *COOH and *CO. The request for improved catalytic performance, however, is motivated by current unsatisfied catalytic selectivity because of the side hydrogen evolution reaction. In this context, the design of Au based binary catalysts that can boost CO selectivity is of great interest. In the present work, we report that Au nanoparticles can be feasibly dispersed and anchored on silicon nanowires to form Au-Si binary nanomaterials. The Au-Si may stably drive CO2RR with a CO Faraday efficiency of 95.6% at −0.6 V vs. RHE in 0.5 mol/L KHCO3 solution. Such selectivity outperforms Au particles by up to 61%. Controlled experiments illustrate that such catalytic enhancement can chiefly be ascribed to electronic effects of binary catalysts. Theoretical calculations reveal that spontaneously produced silicon oxide may not only inhibit hydrogen evolution reaction, but also stabilize the key intermediate *COOH in CO formation.

Comparative characteristics of antimicrobial activity of water dispersions of silver and gold nanoparticles stabilized with native and synthetic polymers

BACKGROUND: The construction and application of antimicrobial drugs on the basis of nanoparticles of metals, silver and gold in particular, are staying casual up to now.
 AIM: was to study the spectrum of antimicrobial activity of nanoparticles of silver and gold developed by means of chemical recovery and stabilized with native and synthetic compounds.
 MATERIALS AND METHODS: The paper presents the results of a study of the antimicrobial activity of aqueous dispersions of silver and gold nanoparticles against standard and clinical strains of Staphylococcus aureus, which were sensitive to methicillin. Natural (carboxymethylcellulose, sodium oleate) and synthetic (polyvinyl alcohol, sodium dodecyl sulfate, polyazolidylammonium modified with iodine hydrate ions) polymeric compounds were used as stabilizers.
 RESULTS: The high antistaphylococcal activity of the studied drugs was established, which depended on the stabilizer used. The highest efficiency of biocidal action was revealed for aqueous dispersions of metal nanoparticles stabilized with polyvinyl alcohol and polyazolidylammonium modified with iodine hydrate ions, which did not depend on the strain differences of microorganisms.
 CONCLUSIONS: The results obtained open up prospects for the use of aqueous dispersions of silver and gold nanoparticles as active components in the development of new antiseptic preparations and photosensitizers for antimicrobial photodynamic therapy.

New Strategy for Creating TiO2 Thin Films with Embedded Au Nanoparticles

This paper proposes a new strategy for producing thin films of TiO2 with embedded gold nanoparticles (TiO2/AuNP). One of the main tasks was the synthesis of a stable dispersion of TiO2 and gold nanoparticles in an aqueous solution of ethylene glycol, suitable for inkjet printing—ink with complex gold nanoparticles (AuCNP ink). The AuCNP were synthesized by a reduction from tetrachloroauric acid in the presence of TiO2 nanoparticles and ethylene glycol (EG). The final formation of TiO2/AuNP films occurred during the annealing of AuCNP layers, inkjet printed on a glass substrate. The TiO2/AuNP films demonstrate absorbance in the yellow-green range due to the localized surface plasmon resonance (LSPR) and are promising for solar cell application.

Plasmon resonance in photoactive P-N junction blend, spin coated from self-made low cost spin coating machine for plastic solar cell

In the present work, spin coated thin films of P3HT: NTCDA donor- acceptor blends of weight ratios 3:1, 1:1 ,1:3 are prepared in Toluene using the self-made spin coating machine. The experiment is focused to optimize the P:N weight ratio of the photoactive blend that can absorb maximum solar energy and also to enhance the absorption by doping it with gold nano particles. Absorption property of the samples are studied using JASCO UV VIS 670 spectrometer which shows that 1:3 blend has the broad spectral response and considered to be the best active blend. The optical band gaps of the samples are determined through Tauc’s plot, wherein the onset wavelength for 1:3 sample is found to be 660nm with a band gap of 1.87 eV. The optimized 1:3 blend is doped with gold nano-particle dispersion in citrate buffer. The absorbance gets increased on doping with nano particle with extremely broadened spectral response which is attributed to the Localized Surface Plasmon Resonance(LSPR). Photons are trapped by the gold particles in the polymer matrix for the efficient harvesting of the solar energy. The construction of the solar cell using this Plasmon enhanced photoactive material is the work under progress. Copyright © 2017 VBRI Press.

Hybrid Multivalent Jack Bean α-Mannosidase Inhibitors: The First Example of Gold Nanoparticles Decorated with Deoxynojirimycin Inhitopes.

Among carbohydrate-processing enzymes, Jack bean α-mannosidase (JBα-man) is the glycosidase with the best responsiveness to the multivalent presentation of iminosugar inhitopes. We report, in this work, the preparation of water dispersible gold nanoparticles simultaneously coated with the iminosugar deoxynojirimycin (DNJ) inhitope and simple monosaccharides (β-d-gluco- or α-d-mannosides). The display of DNJ at the gold surface has been modulated (i) by using an amphiphilic linker longer than the aliphatic chain used for the monosaccharides and (ii) by presenting the inhitope, not only in monomeric form, but also in a trimeric fashion through combination of a dendron approach with glyconanotechnology. The latter strategy resulted in a strong enhancement of the inhibitory activity towards JBα-man, with a Ki in the nanomolar range (Ki = 84 nM), i.e., more than three orders of magnitude higher than the monovalent reference compound.

Improved Sensitivity of Surface-Enhanced Raman Scattering with Gold Nanoparticles-Insulator-Metal Sandwich Layers on Flat Sapphire Substrate.

Surface-enhanced Raman scattering (SERS) as a high sensitivity analytical method for molecule detection has attracted much attention in recent research. In this work, we demonstrated an improved SERS substrate, which has the gold nanoparticles randomly distributed on a SiO2 interception layer over a gold thin film layer on the flat sapphire substrate (AuNP/SiO2/Au/Sapphire), over the dispersed gold nanoparticles on a silicon substrate (AuNP/Si), for detection of R6G (1 × 10−6 M) in a Raman microscope. The fabrication of sandwich layers on top of the sapphire substrate involves evaporation of a gold mirror as thick as 100 nm, plasma enhanced chemical vapor deposition of the silica insulator layer 10 nm thick, and evaporation of a thin gold layer 10 nm thick for forming gold nanoparticles. For comparison, a gold thin film with a thickness of 5 nm and 10 nm was evaporated on a silicon substrate, respectively (AuNP/Si), as the reference SERS substrates in the experiment. The AuNP/SiO2/Au/Sapphire substrate demonstrated improved sensitivity in detection of molecules in Raman microscopy, which can enable the molecules to be recognizable at a low laser power as 8.5 × 10−3 mW, 0.017 mW, 0.085 mW, and 0.17 mW for ultrashort exposure time. The simulation of AuNP/SiO2/Au/Sapphire substrate and AuNP/Si substrate, based on the finite-difference time-domain (FDTD) method, explained the improved sensitivity for detection of R6G molecules from the view of classical electromagnetics, and it suggested the optimized size for the gold nanoparticles and the optimized laser wavelength for Raman microscopy for further research.

Photothermal immunoassay for carcinoembryonic antigen based on the inhibition of cysteine-induced aggregation of gold nanoparticles by copper ion using a common thermometer as readout

The dispersed gold nanoparticles (AuNPs) have weak photothermal effect in near-infrared (NIR) region. After the addition of cysteine, the AuNPs are aggregated due to the electrostatic interaction and then exhibited strong photothermal effect. At present of copper ion (Cu2+), the cysteine was catalytically oxidized into cystine, leading to the inhibition of the aggregation of AuNPs and the photothermal effect decreased. Based on this, a simple photothermal assay can be developed for Cu2+ detection using a common thermometer as readout. The change of the temperature (ΔT) of the system has a linear relationship with Cu2+ in the range of 10–300 nM with a detection limit of 7.4 nM (S/N = 3). Furthermore, through labeling the detection antibody in immunoassay with CuO nanoparticles as the source of Cu2+, a convenient photothermal immunoassay can be developed. Carcinoembryonic antigen (CEA), an important biomarker for cancer screening, was chosen as the model target because the rise of CEA level is widely present in cancer blood serum. Under the optimized conditions, ΔT has a linear relationship with CEA concentration in the range of 3.0–48.0 ng/mL. The detection limit is 1.3 ng/mL. The proposed method had been applied to detect CEA in serum samples with good agreement with the reference method used in hospital.

Graphene Flakes Decorated with Dispersed Gold Nanoparticles as Nanomaterial Layer for ISEs.

This paper proposes a new type of solid-contact layer based on graphene/gold nanoparticles for ion-selective electrodes. A novel approach to preparing the material for intermediate layer by modifying the graphene flakes by gold nanoparticles is presented. With this approach, we observed a large surface area of material and in consequence high electrical capacitance of electrodes. We have obtained satisfactory results demonstrating that the modification of graphene with gold allows for enhancing electrical and wetting properties of carbon nanomaterial. Electrical capacitance of designed nanocomposite-contacted electrode equals to approximately 280 µF, which in consequence ensures great long-term potential stability defined by the potential drift of 36 μV/h. The modification of graphene with nanoparticles completely changed its wetting properties, as the designed material turned out to be hydrophobic with a water contact angle of 115°. Graphene/gold nanoparticles–contacted electrodes are insensitive to the changing light conditions, exhibiting near-Nernstian response in the potassium concentration range between 10−5.9 M and 10−1 M of K+ ions and may be applied in the pH range between 2 and 10.5.

Investigation on synthesis, structural and nonlinear optical responses of cadmium selenide coated with gold nanoparticles induced by femtosecond laser excitation

Nonlinear optical signal enhancement cannot be achieved by using semiconductor materials alone. Here, we show that the recently discovered nonlinear optical behavior of plasmonic nanoparticles and hybrid nanowires enables an enhanced nonlinear optical response. A synthesis, characterization, and nonlinear optical response of synthesized hybrid nanowires structures were studied. The growth of gold nanoparticles (Au NPs) onto cadmium selenide nanowires CdSe NWs with different concentrations of gold nanoparticles coating prepared via an impregnation technique. Au nanoparticles in the CdSe/Au nanowires were uniformly dispersed on the CdSe nanowire surface. The surface morphologies and the propagation manner of hybrid nanostructures were used for transmission electron microscopy (TEM) to study the optical properties of pure and hybrid nanostructures. Dark-field scattering microscopy was used to characterize single CdSe NW and confirm the coating of hybrid CdSe/Au nanowires and characterize the concentration effect of gold nanoparticles. The dark-field scattering spectrum (DFSS) reference to the surface plasmon resonance of nearer Au NPs was observed at ca. 800 nm. By making a comparison between a single cadmium selenide with and without gold nanoparticles coating, hybrid CdSe/Au nanowires exhibit sufficient quality to produce second-harmonic generation stimulated with a pulsed, linearly polarized pump-light from a femtosecond Ti-sapphire laser. The estimated improvement of the second-harmonic generation signal is about ~ 1.8 times, ~ 5.5 times, ~ 6.9 times for low, moderate and full coating of gold nanoparticles, which was mainly due to the high quality of synthesis techniques and good dispersion of gold nanoparticles on CdSe nanowires

Multiple cooperative amplification paper SERS aptasensor based on AuNPs/3D succulent-like silver for okadaic acid quantization

Okadaic acid (OA) is the main toxic component of diarrhetic shellfish poisoning, which can cause vomiting, diarrhea, and even induce tumor formation in people who accidentally ingest it. To strengthen the front-end prevention and control of shellfish safety, a surface-enhanced Raman scattering (SERS) paper swab based on high-affinity binding and high-specific recognition performance of nucleic acid aptamer was proposed to detect OA by virtue of enhanced multistage plasmon coupling effect. Composite resonance bilayer constituted by evenly dispersed gold nanoparticles integrating with a three-dimensional (3D) succulent-like silver particle was facilely manufactured in-situ on the paper substrate. Subsequently, with the assistance of 3D nanotopography structured silver nano-octahedra connected on the signal probe, a multistage SERS signal cooperative amplification platform was formed with about 10-fold enhanced Raman intensity higher than either single-layer substrate. Owning to the unique strategy of superimposed signal enhancement, such paper SERS aptasensor possessed admirable specific recognition and sensitivity has been successfully used in the on-site quantization of OA, with a detection limit of 0.31 ng/mL. Furthermore, the construction of the SERS paper swab is of great significance to the promotion of rapid on-site analysis approach of OA content in seafood by customs, seafood market supervision departments and ordinary consumers.

Aggregation-induced emission of lead halide perovskites modulated by dispersed/aggregated gold nanoparticles for application in the detection of dopamine

A new kind of lead halide perovskites (LHPs) with aggregation induced emission (AIE) feature is developed. These LHPs are nonemissive when they disperse in good solvent (DMF), but show high brightness when they aggregate in water. The morphology of LHPs changes from nanometer-sized irregular shape to micrometer-sized needle-like, and then to stick-like with increasing water fraction. However, their AIE is quenched by only a few pM of dispersed gold nanoparticles (AuNPs). Dopamine (DA) induces aggregation of AuNPs, resulting in AIE recovery of LHPs. A good linear range of DA is obtained from 0.5 to 50 μM with the limit of detection (LOD) 0.12 μM. In the catalysis of tyrosinase (TYR), DA is oxidized to dopaquinone, resulting in the fluorescence quenching of LHPs again. Therefore, this system is further used for monitoring TYR activity and evaluating inhibitor of TYR. Finally, this method is successfully applied to detecting DA in urine samples.

Hard core proof of the polyvinyl alcohol as a reducer for the formation of gold nanoparticles

In this paper, we report the direct synthesis of water dispersed gold nanoparticles encapsulated in polyvinyl alcohol (PVA), which acting as reducer to gold ion to gold metal and capping agent. The syntheses of the gold nanoparticles were carried with the direct addition of the aqueous HAuCl4 solution to aqueous PVA solution at 50 °C. Initially, the PVA solution was prepared by using 2 g of PVA per 100 ml of distilled water in a round bottom flask which was placed in oil bath placed over the magnetic stirrer. Subsequently, the aqueous solution HAuCl4 was added drop-wise to the PVA solution. Afterward, the solution was made viscous by heating at same temperature and casted in form of nanocomposites films. Various compositions of HAuCl4 (0.2 wt%, 0.5 wt%, 1.0 wt% and 1.5 wt%) with respect to PVA (films of Au-PVA nanocomposites) were prepared. Upon drying in ambient condition these films were analyzed with XRD, SEM, EDX, TGA, UV–Visible, and IR techniques. The XRD analysis reveals the fcc crystal structure with crystallite size nearly 22 nm. The crystallite size is in agreement with that obtained by SEM analysis which is in range of 25–30 nm and particles are nearly spherical in shape. Furthermore, the UV–visible analysis showed the surface plasmon resonance (SPR) band at ~ 550 nm which confirmed the formation of gold nanoparticles. It is further supported by the EDX analysis that showed the gold peaks in the spectrum.

Single‐Atom Catalysis: Sustainable Synthesis of Bimetallic Single Atom Gold‐Based Catalysts with Enhanced Durability in Acetylene Hydrochlorination (Small 16/2021)

In article number 2004599, Javier Pérez-Ramírez and co-workers demonstrate that platinum chloride in aqueous solution promotes the dispersion of large gold nanoparticles on carbon carriers into single atoms, forming bimetallic single-atom catalysts with improved resistance against sintering at high temperatures and under the harsh reductive reaction conditions of vinyl chloride production via acetylene hydrochlorination.

Lead halide perovskites with aggregation-induced emission feature coupled with gold nanoparticles for fluorescence detection of heparin

Herein, a new kind of lead halide perovskite (LHP, (C12H25NH3)2PbI4) with aggregation-induced emission (AIE) feature is developed as a fluorescent probe for heparin (Hep). The LHPs exhibit high emission when they aggregate in water. Interestingly, a few picomoles of dispersed gold nanoparticles (AuNPs) can quench the emission of LHPs, but the aggregated AuNPs are invalid. When protamine (Pro) is mixed with AuNPs at first, the negatively charged AuNPs aggregate through electrostatic interaction, producing the AIE recovery. Nevertheless, Hep disturbs the interaction between AuNPs and Pro due to its strong electrostatic interaction with Pro. Therefore, the dispersed AuNPs quench the fluorescence of LHPs again. A response linear range of Hep of 0.8–4.2 ng ml−1 is obtained, and the detection limit is 0.29 ng ml−1. Compared with other probes for determination of Hep with AuNPs, this strategy exhibits better sensitivity due to the small quantity of AuNPs used. Finally, it is also successfully applied to detect Hep in human serum samples with satisfactory recoveries.

Tuning stable noble metal nanoparticles dispersions to moderate their interaction with model membranes

HypothesisThe properties of stable gold (Au) nanoparticle dispersions can be tuned to alter their activity towards biomembrane models. ExperimentsAu nanoparticle coating techniques together with rapid electrochemical screens of a phospholipid layer on fabricated mercury (Hg) on platinum (Pt) electrode have been used to moderate the phospholipid layer activity of Au nanoparticle dispersions. Screening results for Au nanoparticle dispersions were intercalibrated with phospholipid large unilamellar vesicle (LUV) interactions using a carboxyfluorescein (CF) leakage assay. All nanoparticle dispersions were characterised for size, by dynamic light scattering (DLS) and transmission electron microscopy (TEM). FindingsCommercial and high quality home synthesised Au nanoparticle dispersions are phospholipid monolayer active whereas Ag nanoparticle dispersions are not. If Au nanoparticles are coated with a thin layer of Ag then the particle/lipid interaction is suppressed. The electrochemical assays of the lipid layer activity of Au nanoparticle dispersions align with LUV leakage assays of the same. Au nanoparticles of decreasing size and increasing dispersion concentration showed a stronger phospholipid monolayer/bilayer interaction. Treating Au nanoparticles with cell culture medium and incubation of Au nanoparticle dispersions in phosphate buffered saline (PBS) solutions removes their phospholipid layer interaction.

A capacitive humidity sensor based on all-protein embedded with gold nanoparticles @ carbon composite for human respiration detection

Wool and silk fiber are the most extensive resources of protein fibers and have been used in the textile field for many years. The extracted biocompatible proteins are more and more widely used in flexible devices, sensors, tissue engineering, etc. Here, a fully biomaterial based flexible humidity sensor has been successfully fabricated for the first time. Interdigital electrodes of humidity sensor are printed on a transparent sensor substrate made of silk protein by inkjet printing. The humidity sensitive material is gold nanoparticles hosted nitrogen doped carbon (AuNPs@NC), which is fabricated by in situ dispersion of gold nanoparticles in a wool keratin assisted porous carbon precursor. The best treatment condition of the sensitive materials is obtained by comparing the sensitivity of humidity response. Moreover, the as-prepared biocompatible flexible sensor was successfully used to detect human respiration.

Aptamer-Facilitated Design of Gold Nanoparticle-Based Logic Gates for Cyromazine and Melamine Detection in Milk

In this paper, we developed a simply designed detection method for logic gates by using aptamers, cetyltrimethyl ammonium bromide, together with melamine and cyromazine to control the aggregation and dispersion of gold nanoparticles (AuNPs). First, either melamine or cyromazine can induce the aggregation of AuNPs, supporting an OR gate to detect whether they were present or not. Second, based on the fact that aptamer T31 can specifically bind with melamine, preventing the aggregation of AuNPs, an improved INHIBIT gate was also fabricated to find whether there was melamine. It has a detection limit of 0.12 ppm by the naked eye for the detection of melamine, and the limit of detection (LOD) by spectrophotometer is 2.2 ppb. Third, with the adsorption of aptamer Tcy1 on AuNPs and the strong coordination of Tcy1 with cyromazine, the addition of cyromazine and CTAB immediately resulted in the aggregation of AuNPs, giving rise to an AND gate. This gate has a detection limit of 0.17 ppm by the naked eye and the limit of detection (LOD) is 9.0 ppb by spectrophotometer. The system provided a good platform for the development of functional logic systems.