Papers by Keyword: Gold Nanoparticle

Abstract: Abstract. In this paper we report the biological synthesis of gold nanoparticles (GNPs) by the reduction of gold ions using a suspension and supernatant of P. aeruginosa. The biosynthesis method was straightforward and yielded good results without using toxic chemicals. The size distribution of the gold nanoparticles synthesized by P. aeruginosa at higher temperatures was larger than that synthesized at lower temperatures. The GNPs morphology was isotropic at various temperatures. With an increase in the temperature, the stability of the GNPs decreased. The absorption and fluorescence spectra accorded well with the size distribution of the particles, with the nanoparticle size increasing as the absorption and fluorescence increased too. The optical properties of the GNPs observed in the study accorded well with the scanning electron microscopy (SEM) observations. The visible photoluminescence (PL) around 435 nm indicated the possible use of the obtained colloids, which consisted of GNPs and capping biomaterial, in therapeutic applications. Moreover, the synthesized GNPs showed good antibacterial activity toward E. coli indicating their potential in biological applications.

Abstract: Prion protein has drawn great attention due to its pathological potential to prion diseases. Discriminate and detection of the trace quantities PrP^Sc is an important measure for prion disease diagnosis at the presymptomatic stage. In this study, we developed a novel sandwich surface plasmon resonance (SPR) assay for the detection of PrP^Sc, involving bare gold surfaces and bare gold nanoparticles. PrP^Sc can be captured by the SPR sensing surface via a surface assisted coupling reaction between its intra-molecular disulfide bond and the gold atoms, while PrP^C cannot bind to the gold surface strongly. The gold nanoparticles were proved to amplify the SPR detection signals via the coupling of their localized surface plasmon (LSP) with the propagating plasmon on the SPR gold surface. Our results confirmed that the bare SPR gold surface successfully captured the PrP^Sc from the solution with a LOD of 0.5ng/mL and a linear detection range from 0.5ng/mL to 500ng/mL. Injecting the gold nanoparticles after PrP^Sc yielded a dramatic enhancement of signal, with a lower LOD of 0.001ng/mL and a linear detection range from 0.001ng/mL to 10ng/mL. The gold nanoparticles permitted 4 to 322-fold increase of the signals. The required detection time was controlled in 15 min. PrP^C, cys-protein G and their mixtures with PrP^Sc, were also detected via this sandwich SPR detection assay. Atomic force microscope (AFM) was used to evaluate the surface morphology of the SPR gold substrate after the detection. All the obtained results suggested that this novel SPR sandwich detection assay in our work was efficient, sensitive and specific for the detection of trace PrP^Sc

Abstract: In this report, we present a new method for visual and colorimetric detection of Hg (II) ion by using in-situ composited gold nanoparticle (GNP). GNP was formed in one step at room temperature, using NaBH₄ as reducing agent incorporated with 2-[5-(2-aminoethylsulfanyl)-pentylsulfanyl]-ethylamine (5-AEPE) as a stabilizer. A 5-AEPE ligand displayed an effective stabilizer for preventing the aggregation of gold nanoparticle in the absence of Hg (II) ion, showing a rose-red color. On the other hand, in the presence of Hg (II) ion, reduced Hg (0) can also deposit on the surface of gold nanoparticle, resulting solution turn to purple and blue immediately. Based on naked eye detection optimization, 125 μM Au (III), 0.6 mM 5-AEPE, 0.8 mM NaBH₄ and 0.1%(v/v) Triton X-100 was achieved. By measuring at a wavelength of 680 nm, absorbance values increased linearly as two levels of concentration of Hg (II) ion range of 0.125-2.5 μM (low) and 2.5-15 μM (high). This method offer advantage of simplicity, rapidity, cost effectiveness and no requirement of any sophisticated instruments. Moreover, this method has several potential advantages as optical sensor, especially no as-prepared gold nanoparticle synthesis and shorter observation time.

Abstract: A novel near-infrared fluorescence quenching method has been developed for the determination of hydrogen peroxide based on N-acetyl-L-cysteine-capped gold nanoparticles (NAC-AuNPs) as a fluorescence probe. The prepared gold nanoparticles with the size of about 1.91 nm exhibited strong near-infrared fluorescence emission at 693 nm with excitation wavelength at 450 nm in aqueous solution. The fluorescence intensity of NAC-AuNPs was quenched dramatically by adding hydrogen peroxide. Therefore, it could be used to detect hydrogen peroxide based on the fluorescence quenching intensity was linear with the concentration of hydrogen peroxide. Under the optimal experimental conditions, the linear range and detection limit were 1.0×10^-6 –3.0×10^-2 mol/L and 1.0×10^-7 mol/L, respectively. The possible quenching mechanism was investigated by time-resolved fluorescence spectroscopy. The proposed method was simple, sensitive and showed good repeatability and stability.

Abstract: In this article, the relations between extinction cross section and Gold nanoparticle's parameters such as dimensions have been investigated. In this work, the extinction cross section of the core-shell nanoparticles is analyzed by changing the shell material and its thickness. By this, the interesting results such as shifting resonant peak in optical response are obtained. Moreover, a new model of nanostructure is proposed in which the resonant peak of extinction cross section can be controlled by adding silicon nanoparticles and impurity in the shell. This method can be used for tuning of the scattering properties of the core-shell nanoparticle. In the following, we demonstrate that the effective epsilon properties can be used for tuning of the desired optical response in the combinational structure of the spherical nanoparticles. At the end, the effective relative epsilon is also calculated for the selected structures. The operational frequency band is selected from 300 (THz) to 900 (THz).

Abstract: The purpose of this research was to prepare gold nanoparticle (AuNP) modified disposable pencil graphite electrode (PGE). The AuNP was prepared using trisodium citrate reduced gold ion solution. The PGE surface modification was carried out by immersing a bare PGE in poly (diallyldimethylammonium chloride) (PDDA) and then in AuNP solution at room temperature. The characterization of the bare and modified PGE surfaces was carried out using field emission scanning electron microscopy (FESEM) and cyclic voltammetry in the presence of 0.1 M NaOH. The electrochemical behavior of the modified PGE electrode was investigated using cyclic voltammetry, and impedance spectroscopy in the presence of 5 mM [Fe (CN)₆]^3-/4- redox probe solution. The obtained result indicated that the modification of AuNP on the PGE surface provided a good electrochemical signal. In order to obtain more sensitive electrochemical signals, the effect of adsorbed AuNP on the PGE surface was also studied.

Abstract: Synthesis and immobilization of Au nanoparticles (AuNPs) was performed on transparent fluorine-doped tin oxide (FTO) substrate by pulse electrodeposition method. The method was cost effective, simple and capable of producing nanoparticles strongly attached to the substrate. Effects of several influencing factors such as duty cycle, pulse frequency, current density, solution concentration, deposition period and annealing procedure on the optical properties of AuNPs-FTO electrode were investigated. AuNPs-FTO electrodes were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV-Vis absorption analysis. Controllability of the plasmon absorption of the electrodeposited film by tuning of the electrodeposition conditions and thermal annealing procedure was important achievements helpful to the progress of the AuNP film applications in the tunable localized surface plasmon resonance spectroscopy (LSPR) manufacturing industry.

Abstract: The UV and IR block properties of superparamagnetic magnetite nanoparticles (SPMN) and SPMN/gold composite nanoparticles are investigated. The composite nanoparticles were prepared via sonochemical assisted reduction of gold precursor and deposition of gold nanoparticles (GNP) on amine functionalized SPMN. Protective properties of the SPMN and the composite nanoparticles were demonstrated via spectrophotometer measurements. Unlike in the visible and infrared region, there was 0% transmission of radiation through bare SPMN in the UV region. The presence GNP in the composites nanoparticles affects the protecting properties of the SPMN with almost 40% transmission in the UV region. The SPMN/GNP composite nanoparticles were able to block some radiation in the visible region. On the other hand, there was nearly uniform 90% and continuous transmission of infrared rays in naked SPMN and SPMN/GNP composite nanoparticles, respectively.

Abstract: Surface enhanced Raman scattering (SERS) has been proved to be a highly sensitive method to detect organic molecules at very low concentrations. In recent years, many researchers have reported that 1-dimension semiconductor nanomaterials assembled noble metal nanoparticles can get a strong SERS effect. In this paper, we succeeded to synthesize TiO₂ nanorod thin films on fluorine-doped tin oxide (FTO) glass with hydrothermal synthesis which were able to be used as SERS substrates. Gold nanoparticles were assembled to TiO₂ nanorod thin films using the physical sputtering method and the citrate reduction method, respectively. The field emission scanning electron microscope (FESEM) images show that the later method could achieve the more desirable and uniform distribution of gold nanoparticles. Rhodamine 6G (R6G) was chosen as the probe molecule to study the SERS performance of our novel SERS substrates. Raman scattering measurement proved that the substrates were able to enhance Raman signals by several orders of magnitude and could be applied to biochemical detection. The whole fabrication process was facile and cost-effective, and the SERS activity and reproducibility of the substrates were pretty good.

Abstract: The optical properties of triangular gold nanoparticle pairs are investigated by numerical simulations using Finite-difference time-domain (FDTD) method. The simulation results show the significant red shifts of plasmon resonances as the size of nanoparticle is increased. The large electric field enhancement is also verified by calculating the local electric field distributions.