STUDY ON THE INTERACTION BETWEEN POLYVINYLPYRROLIDONE AND PLATINUM METALS DURING THE FORMATION OF THE COLLOIDAL METAL NANOPARTICLES

Several PVP-stabilized colloidal platinum metals nanoparticles have been synthesized and characterized by FTIR and TEM.Comparing with the pure PVP,carbonyl groups of PVP in the mixture of PVP and the metal precursors or in the PVP-stabilized metal nanoparticles have obvious peak shifts in FTIR spectra.The peak shifts reveal the interaction between PVP and the metal species.The interaction between PVP and metal precursors has effect on the formation of the colloidal metal nanoparticles.Strength of the intera...

Surface Plasmon Resonance Enhanced Scattering of Au Colloidal Nanoparticles

Suspended gold nanoparticles have been synthesized via electrochemical method. The strongest resonance scattering peak is at 485 nm, which results from the surface plasmon resonance. When the excited wavelength is at 242 nm (12.4 × 1014 Hz), there have been a 1/2 fraction frequency scattering peak at 485 nm (1/2 × 12.4 × 1014 Hz) and a 1/3 fraction frequency scattering peak at 726 nm (1/3 × 12.4 × 1014 Hz) displayed. Emission spectra with different particle diameters were compared, the intensity of scattering light increases with the particle size. The frequency-dependent scattering average cross section of small particle was calculated from Mie theory. The model calculation is in agreement with the experimental results.

Determination of Particle Sizes and Crystalline Phases on Colloidal Silicon Nanoparticle Suspensions

Particle size and crystallinity of silicon nanoparticles were determined by analyzing the optical extinction spectra of colloidal suspensions. Experimental results from these colloids were anaiyzed using Mie theory in connection with effective medium theory, in order to determine particle sizes and their internal structure with the simple technique of optical transmission spectroscopy. By modeling an effective refractive index for the particles, the crystalline volume fraction can be extracted from extinction spectra in addition to information about the size. The crystalline volume fraction determined in this way were used to calibrate the ratio of the Raman cross sections for nanocrystalline and amorphous silicon, which was found to be σc./σa = 0.66

Influence of Single Use and Combination of Reductants on the Size, Morphology and Growth Steps of Gold Nanoparticles in Colloidal Mixture

A comprehensive investigation on the formation mechanism of gold nanoparticles (AuNPs) in colloidal mixture obtained from the reduction of chloroauric acid (HAuCl4) solution using a single reducing agent (sodium citrate;process-I), (tannic acid;process-II), and a combination of two reducing agents (sodium citrate plus tannic acid;process-III) is reported. The growth steps at different time intervals during synthesis of colloidal AuNPs were monitored in situ and ex situ using various methods for all the three processes. The measurement of changes in the surface plasmon band position of colloidal AuNPs, along with dynamic light scattering results gave important information for the first assessing of particle size, shape and distribution. Besides, the size and morphological changes at different stages during different processes were also analyzed by transmission electron microscopy. The final Au particles of processes-I & II exhibited different shapes (spherical and nanowires) with particle size and nano wire diameter of 12 nm and 17 nm, respectively. Nevertheless, combination of two reductants (process-III) surprisingly leads to drastically reduced size (ca. 3 nm) with spherical morphology compared to their parent solutions with either of single reducing agent. This result clearly indicates that the combination of reductants has a significant influence on the particle size, morphology and formation mechanism.

Electrochemical Aptasensor Based on Prussian Blue-Chitosan-Glutaraldehyde for the Sensitive Determination of Tetracycline

In this paper, a novel and sensitive electrochemical aptasensor for detecting tetracycline(TET)with prussian blue(PB) as the label-free signal was fabricated. A PB-chitosan-glutaraldehyde(PB-CS-GA)system acting as the signal indicator was developed to improve the sensitivity of the electrochemical aptasensor.Firstly, the PB-CS-GA was fixed onto the glass carbon electrode surface. Then, colloidal gold nanoparticles(Au NPs) were droped onto the electrode to immobilize the anti-TET aptamer for preparation of the aptasensor.The stepwise assembly process of the aptasensor was characterized by cyclic voltammetry(C-V) and scanning electron microscope(SEM). The target TET captured onto the electrode induced the current response of the electrode due to the non-conducting biomoleculars. Under the optimum operating conditions, the response of differential pulse voltammetry(DPV) was used for detecting the concentration of TET. The proposed aptasensor showed a high sensitivity and a wide linear range of 109-～ 105-M and 105-～ 102-M with the correlation coefficients of 0.994 and 0.992, respectively. The detection limit was 3.2×1010-M(RSD 4.12%). Due to its rapidity, sensitivity and low cost, the proposed aptasensor could be used as a pre-scanning method in TET determination for the analysis of livestock products.

Characterization of colloidal arsenic at two abandoned gold mine sites in Nova Scotia, Canada, using asymmetric flow-field flow fractionation-inductively coupled plasma mass spectrometry

Asymmetric flow-field flow fractionation-inductively-coupled plasma-mass spectrometry was used to determine whether colloidal arsenic（As） exists in soil pore water and soil extract samples at two arsenic-contaminated abandoned gold mines（Montague and Goldenville, Nova Scotia）. Colloidal arsenic was found in 12 out of the 80 collected samples（= 15%）, and was primarily associated with iron（Fe） in the encountered colloids. The molar Fe/As ratios indicate that the colloids in some samples appeared to be discrete iron–arsenic minerals, whereas in other samples, they were more consistent with As-rich iron（oxy）hydroxides. Up to three discrete size fractions of colloidal As were encountered in the samples, with mean colloid diameters between 6 and 14 nm. The pore water samples only contained one size fraction of As-bearing colloids（around 6 nm diameter）, while larger As-bearing colloids were only encountered in soil extracts.

Glucose oxidase as a blocking agent-based signal amplification strategy for the fabrication of label-free amperometric immunosensors

An effective electrochemical signal amplification strategy based on enzyme membrane modification and redox probe immobilization was proposed to construct an amperometric immunosensor.L-cysteine@ferrocene functionalized chitosan,which possessed not only efficient redox-activity but also excellent film-forming ability,was coated on the bare glass carbon electrode. Moreover,the thiol groups(SH)in the ferrocenyl compound were used for gold nanoparticles immobilization via the strong bonding interaction,which could further be utilized for the immobilization of antibody biomolecules with well-retained bioactivities.Finally,glucose oxidase(GOD)as the enzyme membrane was employed to block the possible remaining active sites and avoid the nonspecific adsorption.With the excellent electrocatalytic properties of GOD towards glucose,the amplification of antigen-antibody interaction and the enhanced sensitivity could be achieved.Under the optimal conditions,the linear range of the proposed immunosensor for the determination of carcinoembryonic antigen(CEA)was from 0.05 to 100 ng/mL with a detection limit of 0.02 ng/mL(S/N=3).Moreover,the immunosensor exhibited good selectivity,stability and reproducibility, which provided a promising potential for clinical immunoassay.

Zeta potential measurement on lithium lanthanum titanate nanoceramics

The zeta potential, isoelectric point, and agglomeration of Lio.sLao.sTiO3 （LLTO） nanoparticles dispersed in aqueous media at different ionic strengths have been studied. The zeta potential was determined from electrophoretic mobility measurements, according to Smoluchowski＇s equation, for Li0.5La0.5TiO3 suspen- sions in NaCl and KCI electrolytes with ionic strengths of 1, 10, and 100 mmol/dm3. The isoelectric point （IEP）, zeta potential （ζ）, and the agglomeration were shown to strongly depend on the ionic strength of the Li0.5La0.5TiO3 aqueous colloidal suspension in both NaCI and KCI electrolytes, which allows the deter- mination of the effects of environmental conditions for Lio.sLao.sTiO3 manipulation in aqueous colloidal systems. The suspensions of Li0.5La0.5TiO3 nanoparticles reach the IEP in the pH range 0f3-5. The （ of Li0.5La0.5TiO3 nanoparticles varied from positive to negative values with a pH increase, which allows for the control of the surface charge depending on the purpose. The pH range of 7-g and an ionic strength ≤1 mmol/dm3 are recommended as the most suitable conditions for both the LLTO colloidal shaping techniques application and the LLTO-based nanocomposite formation.