Anisotropic gold nanoparticles: Preparation and applications in catalysis

Despite the high amount of scientific work dedicated to the gold nanoparticles in catalysis, most of the research has been performed utilising supported nanoparticles obtained by traditional impreg‐nation of gold salts onto a support, co‐precipitation or deposition‐precipitation methods which do not benefit from the recent advances in nanotechnologies. Only more recently, gold catalyst scien‐tists have been exploiting the potential of preforming the metal nanoparticles in a colloidal suspen‐sion before immobilisation with great results in terms of catalytic activity and the morphology con‐trol of mono‐and bimetallic catalysts. On the other hand, the last decade has seen the emergence of more advanced control in gold metal nanoparticle synthesis, resulting in a variety of anisotropic gold nanoparticles with easily accessible new morphologies that offer control over the coordination of surface atoms and the optical properties of the nanoparticles （tunable plasmon band） with im‐mense relevance for catalysis. Such morphologies include nanorods, nanostars, nanoflowers, den‐dritic nanostructures or polyhedral nanoparticles to mention a few. In addition to highlighting newly developed methods and properties of anisotropic gold nanoparticles, in this review we ex‐amine the emerging literature that clearly indicates the often superior catalytic performance and amazing potential of these nanoparticles to transform the field of heterogeneous catalysis by gold by offering potentially higher catalytic performance, control over exposed active sites, robustness and tunability for thermal‐, electro‐and photocatalysis.

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.

Preparation and Characterization of Nimodipine-loaded Methoxy Poly(ethylene glycol)-poly(lactic acid) Diblock Copolymer Nanoparticles

Amphiphilic diblock copolymers, methoxy poly （ ethylene glycol）-poly（lactic acid） （MePEG-PLA）, were synthesized from monomers of DL-lactide and methoxy poly （ethylene glycol） by a ring opening bulk polymerizatiou in the presence of stannous octoate. Their chemical structure and physical properties were investigated using FTIR, NMR, GPC, and fluorescence spectroscopy. To estimate the feasibility as colloidal drug carrier, nimodipine （ND） was loaded into MePEG-PLA block copolymer nanoparticles by phaseseparation/dialysis method. The mean diameter and drug loading efficiency of ND-loaded MePEG-PLA copolymer nanoparticles depended ou PLA/MePEG block composition of the copolymer and drug/polymer feed ratio in preparatiou. NMR study confirmed that nimodipine was entrapped into the hydrophobic inner core of MePEG-PLA copolymer nanoparticles and hydrophilic PEG chains were located ou the surface of the drug-loaded polymer nanoparticles. In vitro release experiments exhibited the sustained release behavior of nimodipine from MePEG-PLA copolymer nanoparticles, without any burst effect.

Optical Nonlinearity of Surface Plasmon Resonance Emission from Au Colloidal Nanoparticles

Suspended gold nanoparticles have been synthesized via electrochemical method.Fluorescence excitation and emission spectra were obtained using a spectrofluorophotometer.With varying the excitation wavelength,an emission peak fixed at 485 nm has always been observed.We believe that this peak is attributed to the surface plasmon resonance.When the detection wavelength was fixed at 485 nm (0.619×10 15 Hz),a double frequency exciting peak at 242 nm(2×0.619×10 15 Hz), a 3/2 fraction frequency exciting peak at 330 nm (about 3/2×0.619×10 15 Hz)and a 3/4 fraction frequency exciting peak at 640 nm(3/4×0.619×10 15 Hz)display.The nonlinear exciting peak at 640 nm corresponds to the two-photon absorption.Therefore,as the excitation wavelength is at 320 and 640 nm respectively,single-photon and two-photon absorption induced surface plasmon resonance emission peaks were observed. These nonlinear surface plasmon resonance emission characters of Au colloidal nanoparticles make it possible to enhance the sensitivity of conventional surface plasmon resonance device.

Investigation of Influence of Magnetic Nanoparticles on the Quality-Factor of the Oscillatory Circuit

In this study, author investigated the spectral response of EM （electromagnetic） energy absorption in a colloidal system of Fe3O4 nanoparticles with an average size of 9.50 nm immersed in a 2% aqueous solution of SDS （sodium dodeci[ sulfate）. The temperature of the nanoparticles and the SDS solution was evaluated by a novel method based on measuring the Q-factor （quality-factor） of a resonant circuit. The Q-factor of the investigated system as a function of the frequency of the EM field was obtained. The nanoparticles-SDS liquid system exhibited a resonance-like behavior of the absorption, where the resonance frequency was about 170 MHz, and the absorption rise up to the resonance frequency was rather slow. The observed absorption of EM energy was accompanied by a small temperature increasing of the system. Measurements of the ESR （electron spin resonance） spectrum of the Fe3O4 nanoparticles have presented a slightly asymmetric singlet with the proportionality factor g = 2 and a line-width of the magnetic field strength △H = 0.1 mT. It was shown that the observed absorption spectrum corresponds to paramagnetic behavior of the investigated nanoparticles.

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.

A bioactive nanocomposite integrated specific TAMs target and synergistic TAMs repolarization for effective cancer immunotherapy

Reactive oxygen species(ROS)generated from photosensitizers exhibit great potential for repolarizing immunosuppressive tumor-associated macrophages(TAMs)toward the anti-tumor M1 phenotype,representing a promising cancer immunotherapy strategy.Nevertheless,their effectiveness in eliminating solid tumors is generally limited by the instability and inadequate TAMs-specific targeting of photosensitizers.Here,a novel core-shell integrated nano platform is proposed to achieve a coordinated strategy of repolarizing TAMs for potentiating cancer immunotherapy.Colloidal mesoporous silica nanoparticles(CMSN)are fabricated to encapsulate photosensitizer-Indocyanine Green(ICG)to improve their stability.Then ginseng-derived exosome(GsE)was coated on the surface of ICG/CMSN for targeting TAMs,as well as repolarizing TAMs concurrently,named ICG/CMSN@GsE.As expected,with the synergism of ICG and GsE,ICG/CMSN@GsE exhibited better stability,mild generation of ROS,favorable specificity toward M2-like macrophages,enhancing drug retention in tumors and superior TAMs repolarization potency,then exerted a potent antitumor effect.In vivo,experiment results also confirm the synergistic suppression of tumor growth accompanied by the increased presence of anti-tumor M1-like macrophages and maximal tumor damage.Taken together,by integrating the superiorities of TAMs targeting specificity and synergistic TAMs repolarization effect into a single nanoplatform,ICG/CMSN@GsE can readily serve as a safe and high-performance nanoplatform for enhanced cancer immunotherapy.

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.

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.

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.