Papers by Keyword: Gold Nanoparticles (GNP)

Abstract: This study presents a simple and low-cost spray coating process for producing high performance CO (carbon monoxide) sensors utilizing toluene-based gold nanoparticles (Au-NPs). Thanks to the success synthesis of Au-NPs in toluene, this low surface tension organic solvent prevents Au-NPs from colligation. And therefore Au-NPs can be well dispersed on the surface of the electrodes as the sensing layer during spraying. To compare with the typical metal oxide based CO sensors that have to work at a higher working temperature of about 150~350°C, the produced sensor can work at room temperature and have a better detection limit for CO gas (5 ppm). Experimental results indicate good linear sensitivity under repeated measurements for concentration range from 5 250 ppm (R²=0.996). The repeatability is also confirmed by measuring 100 ppm CO gas, the calculated variation is less than 2.8% for six repeating measurements. The process developed in this study can be used to produce not only high performance CO gas sensors but other related gas sensors.

Abstract: Coralyne is a kind of protoberberine alkaloids with strong anticancer activity in animal models, which could induce single-stranded adenine rich nucleic acids (poly (dA)) to form a duplex structure. And poly (dA) could be absorbed on the surface of gold nanoparticles (AuNPs) to enhance the stability against NaCl induced aggregation. However, coralyne induced poly (dA) to form double-stranded DNA, which then left the AuNPs resulting in the arrgregation by NaCl. This paper investigated the conditions and effects of using poly (A40) as a probe for the coralyne detection. The detection of coralyne used 100 mM HEPES and 200 mM NaCl as the buffer solution. The poly (A40) was 250 nM in the experiment for the protection of AuNPs aggregation caused by buffer solution. UV-visible spectroscopy was employed to detect the colorimetric changes in the aggregated condition of AuNPs. From blank to 1000 nM of coralyne, a linear response was obtained with R² = 0.862. The limit of detection was 100 nM. Results showed that the detection of coralyne with poly (A40) was achievable by using unmodified AuNPs.

Abstract: A liquid phase method to synthesize gold nanoparticles (NPs) has been studied by reducing tetrachloroauric acid (HAuCl₄) with the culture medium of baker’s yeast. In general, the reducing substances in the culture medium of baker’s yeast can be divided into two categories: the metabolites and the organizations. Herein the reducing agents are mostly metabolites, along with some other components of the cells that are overlooked in the process of filtering. Different sizes of gold NPs have been obtained by merely varying pH of the medium, with size of the nanoparticles of 5~30 nm. Several characterizations have been carried out to confirm and analyze our products, such as UV-vis spectra, field emission scanning electron microscope (FE-SEM) images, transmission electron microscope (TEM) image, energy dispersive spectrum (EDS) and selected area electron diffraction (SAED) patterns. In the future study, the smaller ones can be treated as a good substitute of the traditional seeds synthesized with some chemical surfactants.

Abstract: The size and shape of gold nanoparticles controlled by pH was studied in the reacted solutions containing peptides (NH₂-Leu-Aib-Trp-Ome) as reducing agent. The resulting gold nanostructures were characterized by transmission electron microscopy (TEM), XRD and UV-vis-NIR spectra. Different shape of gold nanoparticles such as spheres, multipod and branch were prepared by changing the pH of solution. The resulting gold nanostructures may be have potential applications in the Surface Enhanced Raman Spectroscopy (SERS) and NIR-absorbing filters and coatings.

Abstract: The gold nanoparticles film has been successfully formed on the silicon wafer by self-assembled method. The gold colliods were prepared by chemical reduction method where sodium citrate (act as the reducing, capping and stabilizing agent) were added into the boiling 50ml of 0.01% tetrachloroauria acid (HAuCl₄) solution in reflux system. Different particle size of gold colloids (AuNPs_1 and AuNPs_2) were produced by altering the amount of sodium citrate. The as-prepared gold colloids were characterized by UV - Vis spectrometry, Malvern particle size analyzer, zeta potential and XRD. Self-assembled method of Au nanoparticles were first start with the cleaning of silicon wafers using standard RCA cleaning, and followed by the piranha treatment to producing an OH-terminated surface. Then, the wafers were functionalized with organosilane molecule by immersing the silicon wafer in 10mM of surfactant in methanolic solution to produce self-assemble monolayers (SAMs) on silicon wafer surface. These layers were used to immobilize the gold nanoparticles from as-prepared gold colloid and result of the gold nanoparticles film on silicon wafer. Effect of surfactant ((3-aminopropyl) trimethoxysilane (APTMS) and (3-mercaptopropyl) trimethoxysilane (MPTMS)), effect of particle size of gold colloid (AuNPs_1 and AuNPs_2) and the effect of deposition time (0.5, 1.0, 1.5 and 2 hours) to the surface morphology such as surface coverage, inter-particle distance were studied in this work. The surface morphology of gold nanoparticles films were characterized by FESEM and AFM.

Abstract: A simple, fast and reliable colorimetric method for melamine detection based on gold nanoparticles (AuNPs) and poly-thymine (poly-T) is reported. Poly-T strands attract AuNPs through static electricity and keep them stable against aggregation in the presence of NaCl. The affinity between melamine and poly-T, hydrogen bond, frees AuNP from the protection provided by poly-T and thus makes AuNPs aggregate in the presence of NaCl. The color change of AuNPs from wine red to blue can be observed immediately by the naked eye during the aggregation process, and can be accurately recorded with the help of a UV/vis spetrophotometer within 5 minutes. The limit of detection (LOD) of melamine in pure water is 0.146 μmol/L with a linear range from 0.2×10^-7 mol/L to 10.0×10^-7 mol/L. In fresh milk and milk powder, the LOD is respectively as low as 2.37 μmol/L and 5.36 μmol/L.

Abstract: Hemin aptamer was used to modify gold nanoparticles (AuNPs) to obtain a stable aptamer-nanogold probe (AussDNA). In the condition of pH 8.0 Tris-HCl buffer solution containing 50mmol/L NaCl, the substrate chain of AussDNA was cracked by hemin to produce a short single-stranded DNA(ssDNA) and then further combined with hemin to form a stable hemin-ssDNA conjugate. The AuNPs released from AussDNA would be aggregated in the condition of 50mmol/L NaCl and exhibited a strong resonance Rayleigh scattering (RRS) peak at 368nm. Under the selected conditions, the increased RRS intensity (ΔI_368nm) was linear to hemin concentration in the range of 5-750nmol/L, with a detection limit of 66 pmol/L. This RRS method was applied to determination of residual hemin in serum samples, with satisfactory results. The remnant AussDNA in the solution exhibited a strong catalytic activity on the gold particle reaction of HAuCl₄-vitamine C (VC) that can be monitored by RRS technique at 368 nm. When the hemin concentration increased, the AussDNA decreased, the catalysis decreased, and the RRS intensity at 368nm decreased. The decreased RRS intensity ΔI_368nm was linear to the hemin concentration in the range of 1-200nmol/L, with a detection limit of 54 pmol/L. Accordingly, a sensitivity, selectivity, and simplicity new method of resonance Rayleigh scattering spectra to detect hemin using aptamer-modified nanogold as catalyst was established.

Abstract: In 6 mol/L HCl medium, TeO₄^2- is reduced by NaH₂PO₂ to Te that catalyze NaH₂PO₂ reducing HAuCl₄ to form gold nanoparticles (AuNPs), which exhibited a strong resonance Rayleigh scattering (RRS) peak at 370 nm. With the TeO₄^2- concentration increased, the catalytic reaction enhanced and formed more AuNPs that resulting in the RRS peak increased. Under the chosen conditions, the RRS intensity at 370 nm enhanced linearly with the concentration of TeO₄^2- in the range of 12.5-287.5 nmol/L. This RRS method was sensitivity, selectivity, and simplicity.

Abstract: In this research, effects of soaking time in melting glass process on red color development have been investigated. The red glasses were prepared from gold nanoparticles (AuNPs) with compositions of 70.475SiO₂ : 11Na₂O : 9CaO : 9K₂O : 0.005SeO₂ : 0.5SnO₂ : 0.02AuNPs % by weight and vary soaking time at 1 to 5 hours. The glasses were melted the normal melt-quench technique. The color of glasses were measured by uv-visible spectrophotometer in the wavelength range 300-900 nm and color coordinate in CIEL*a*b* system. The result found that, the glasses sample with 1 and 2 hours of soaking time are shown purple color. At 3, 4 and 5 hours of soaking time are shown red color. The results reflecting that the particle size of gold particle in glass matrices at 3, 4 and 5 hours are smaller than 1 and 2 hours of soaking time.

Abstract: Gold nanoparticles were synthesized by two bolaform cholesteryl imide derivatives with different lengths of ethyleneamine spacers at a liquid-liquid interface. By stirring the aqueous solution containing AuCl₄^- ions with the chloroform solution of bolaform amphiphile, AuCl₄^- ions were transferred into the organic phase and reduced to gold nanoparticles. Spectral and morphological measurements indicated that both bolaform amphiphiles could serve as both capping and reducing agents. Different gold nanostructures could be obtained depending on the different spacers and the molar ratios of amphiphile to AuCl₄^- ions.