Thermostability of modified enzymes: a detailed study

Three enzymes (lysozyme, EC 3.2.1.17; α‐chymotrypsin, EC 3.4.21.1; and Candida rugosa lipase, EC 3.1.1.3) have been modified in order to alter their surface hydrophobic/hydrophilic balance in opposite directions, by chemoenzymatic glycosylation and chemical binding of polyethylene glycol (PEG). The thermal stability in aqueous environment of the produced biocatalysts was studied, and two different approaches were considered: the determination of half‐life times and the mechanistic analysis of the deactivation kinetics. The comparison of half‐life times indicated that an increase in enzyme surface hydrophobic character induced a remarkable amelioration in thermostability, while the increase in hydrophilic character produced the opposite effect. However, the investigation of kinetic and thermodynamic parameters of enzyme deactivation revealed, in some cases, secondary stabilisation effects during some step of the mechanism, which would not have been detected if only half‐life times had been considered. © 1999 Society of Chemical Industry     

Magnetism in gold nanoparticles

Gold nanoparticles currently elicit an intense and very broad research activity because of their peculiar properties. Be it in catalysis, optics, electronics, sensing or theranostics, new applications are found daily for these materials. Approximately a decade ago a report was published with magnetometry data showing that gold nanoparticles, most surprisingly, could also be magnetic, with features that the usual rules of magnetism were unable to explain. Many ensuing experimental papers confirmed this observation, although the reported magnetic behaviours showed a great variability, for unclear reasons. In this review, most of the experimental facts pertaining to "magnetic gold" are summarized. The various theories put forth for explaining this unexpected magnetism are presented and discussed. We show that despite much effort, a satisfying explanation is still lacking and that the field of hypotheses should perhaps be widened.     

Synthesis of silicon nanoparticles with a narrow size distribution: A theoretical study

This work presents a study of the processes involved in synthesis of narrowly distributed silicon nanoparticles from the thermal decomposition of silane. Two models are proposed, one which simultaneously solves the kinetic mechanism of Swihart & Girshick (1999, Journal of Physical Chemistry B 103, 64–76) while adjusting the sintering parameters; and another which adjusts the kinetic and surface growth mechanisms while neglecting coagulation and sintering. The models are applied to simulate the centreline of the hot-wall reactor and process conditions of Körmer et al. (2010, Journal of Aerosol Science 41, 998–1007). Both models are shown to give good agreement with experimental PSDs at a range of process conditions. However, it is reported that an unphysical sintering process is obtained when attempting to use Swihart & Girshick's kinetic mechanism, while solving for the sintering parameters. The model with adjusted gas-phase and surface growth processes gives better quantitative and qualitative agreement with experimental results. It is therefore recommended that further study into the kinetic and heterogeneous growth mechanisms be conducted in order to better understand the fundamental processes occurring in this hot-wall reactor.     

Peptide-capped gold nanoparticles: towards artificial proteins

Peptides can be designed to form self-assembled monolayers on gold nanoparticles to give nanomaterials with some chemical properties analogous to those of proteins. A variety of molecular-recognition properties are readily integrated within the peptide monolayer. Monofunctionalized nanoparticles are obtained by using separation methods that have been optimized for proteins. Recent applications as artificial enzymes and artificial enzyme substrates are presented. The limitations and long-term potential of peptide-capped nanoparticles as artificial proteins are discussed.     

Size control of gold nanoparticles synthesized in a DNA hydrogel

A DNA crosslinked hydrogel, which efficiently absorbs Au³⁺, was used as a ‘reactor’ for in‐gel synthesis of gold nanoparticles. Chemical reduction of Au³⁺ absorbed by the DNA hydrogel proceeds inside the hydrogel volume and yields well‐dispersed gold nanoparticles with a narrow size distribution. The average diameter of the nanoparticles varies from 1 to 2 to 5 nm on changing the pH during the reduction. The electrostatic properties of DNA hydrogels containing gold nanoparticles are discussed. © 2014 Society of Chemical Industry     

A novel class of potential prion drugs: preliminary in vitro and in vivo data for multilayer coated gold nanoparticles

Gold nanoparticles coated with oppositely charged polyelectrolytes, such as polyallylamine hydrochloride and polystyrenesulfonate, were examined for potential inhibition of prion protein aggregation and prion (PrPSc) conversion and replication. Different coatings, finishing with a positive or negative layer, were tested, and different numbers of layers were investigated for their ability to interact and reduce the accumulation of PrPSc in scrapie prion infected ScGT1 and ScN2a cells. The particles efficiently hampered the accumulation of PrPSc in ScN2a cells and showed curing effects on ScGT1 cells with a nanoparticle concentration in the picomolar range. Finally, incubation periods of prion-infected mice treated with nanomolar concentrations of gold nanoparticles were significantly longer compared to untreated controls.     

Computer simulations and in vivo convection-enhanced delivery of fluorescent nanoparticles demonstrate variable distribution geometry

ObjectiveConvection-enhanced delivery (CED) has emerged as a promising technique for bypassing the blood–brain barrier to deliver therapeutic agents. However, animal studies and clinical trials that utilize the technique suggest that it may require further optimization before it can be safely used in humans. In particular, while volume of distribution in the target tissue can be controlled, the geometrical spread into a desired target region is highly variable from experiment to experiment. In the present paper we have sought to characterize the non-uniform distribution geometry using fluorescent nanoparticles in both a rat model and computer simulations.MethodsUsing diffusion tensor imaging MRI data of the rat brain, we performed computer simulations of a 0.5 μL/min CED infusion. A step design catheter targeting the striatum was simulated to infuse 20 μL of infusate. Using the same infusion parameters, we then performed in vivo CED experiments where we infused fluorescently labeled polyethylene glycol-polylactide-polycaprolactone nanoparticles (FPNPs) into the rat striatum. Fluorescence microscopy was used to examine the distribution geometry histologically.ResultsThe computer simulations demonstrated large variations in distribution patterns when catheter placement was shifted by only 1 mm. Animal infusions also exhibited highly irregular and variable distribution geometries despite the use of relatively small flow rates.ConclusionComputer simulations and repeated in vivo infusions demonstrate the difficulty of achieving desired drug distribution in target tissue. We have proposed a calculation for sphericity which, along with the ubiquitous volume of distribution measure, may prove helpful in describing distribution geometry. Taken together, our results suggest that CED's limitations must be considered and further optimization may be required before the technique sees widespread use in humans.     

Grain size effects in polycrystalline gold nanoparticles

We report a structure-property relationship in gold nanoparticles (NPs), grain-size effects, which not only allow material properties observed on different characteristic length scales to be engineered in a single NP but further enhance those properties due to the coupling among different-size grains. The grain size effects were achieved by creating polycrystalline gold NPs (pAuNPs) with two distinct grain-size populations (5 and 1 nm) comparable to electron mean free path and electron Fermi wavelength (EFW), respectively. Successful integration of molecular and plasmonic properties into a single nanostructure without additional fluorophores enables these highly polycrystalline AuNPs to serve as multimodal probes in a variety of optical microscopic imaging techniques.     

XPS and reactivity study of bimetallic nanoparticles containing Ru and Pt supported on a gold disk

We report a new method of immobilization of catalytic metal/alloy nanoparticles on a gold disk for transfer from an electrochemical cell to UHV (without sample exposure to air) for XPS analyses. Using this immobilization approach, several samples were examined: a core-shell Pt-on-Ru catalyst prepared from Ru black onto which Pt was spontaneously deposited, commercial Pt/Ru 50:50 nanoparticle alloy, as well as single metal Ru and Pt nanoparticle samples. The catalysts were characterized for the Ru oxidation state and for the methanol electrooxidation activity (as Pt was always metallic). For all bimetallic samples, we found that the reduced nanoparticles were more active towards methanol oxidation than the fully or partially oxidized samples. Regardless the Ru oxidation state however, the activity was lower than that previously reported for Ru decorated Pt nanoparticle catalysts (Ru-on-Pt). Possible reasons for the reactivity differences are discussed.     

Catalytically active gold: from nanoparticles to ultrathin films

Ordered gold (Au) mono- and bilayer structures have been synthesized on a highly reduced titania surface. The Au bilayer exhibits a significantly higher catalytic activity for carbon monoxide oxidation than does the Au monolayer structure. This is the first report of Au completely wetting an oxide surface and demonstrates that ultrathin Au films on an oxide surface have exceptionally high catalytic activity, comparable to the activity observed for Au nanoparticles. This discovery is a key to understanding the nature of the active site of supported Au catalysts.     

Size-dependent direct electrochemical detection of gold nanoparticles: application in magnetoimmunoassays

The effect of the AuNPs size, ranging from 5 nm to 80 nm, on the electrochemical response of screen-printed carbon electrodes (SPCEs) used as electrochemical transducers is investigated for the first time. A simple hydrodynamic modelling and calculation at the nanoscale level is applied so as to find the effect of the size of AuNP upon the electrochemical response. The results show that the best electrochemical response for AuNP suspension for the same concentration of total gold is obtained for the 20 nm sized nanoparticles. It is concluded that the Brownian motions avoid a better response for smaller AuNPs that should in fact be related with the best electrochemical signal due to their higher surface area. Finally, the size effect is studied for AuNPs acting as electroactive labels in an immunosensor that employs magnetic beads as platforms of the bioreactions. The best response for the 5 nm AuNPs in this case is due to the fact that in the immunosensing conditions the Brownian motions are minimized because the AuNPs contact with the electrotransducer surface is induced by the immunoreaction and the fast magnetic collection of the nanoparticles used as antibody labels upon application of a magnetic field.     

Self-assembled organic monolayers on gold nanoparticles: A study by sum-frequency generation combined with UV-vis spectroscopy

We use sum-frequency generation spectroscopy (SFG) in the infrared 2800-3000 cm⁻¹ spectral range and UV-vis spectroscopy (transmission) in the 450-650 nm spectral range in order to characterize vibrational and electronic properties of various interfaces composed of organic monolayers adsorbed on gold nanoparticles (AuNPs) with 19 nm average diameter. SFG signal is observed for AuNPs films deposited on glass substrates using the following silane intermediates: 3-(aminopropyl) triethoxysilane and 3-(mercaptopropyl) trimethoxysilane. The density of AuNPs and their aggregates are measured with a scanning electron microscope. For the samples showing a strong well-defined surface plasmon resonance (SPR), we also observe an enhancement of their non-linear optical properties. Furthermore, the SFG measurements show that 1-dodecanethiol films are rather well ordered on specific AuNPs substrates. In this way, the presence of the SFG signal, which comes from both the bulk electronic s-d interband transition and the vibrational states of the adsorbed molecules, depends on a SPR process. This phenomenon is evidenced on the AuNPs by the incident visible beam located at 532 nm, i.e. near the SPR energy maximum of these interfaces. These results open the door to experiments involving macromolecular and biological materials networks deposited on ultrathin metal electrodes in a controlled electrochemical environment.     

Synthesis of gold nanoparticles in hyperbranched polyol dispersions

In this study, a series of different generation hyperbranched poly(amine‐ester) with hydroxyl as terminal group were synthesized and used as protectants to synthesize gold nanoparticles with a facile and highly reproducible method. The effect of hyperbranched poly(amine‐ester) generation on size and their distribution of gold nanopartciels were discussed. The results of ultraviolet visible absorption spectroscopy, Transmission electron microscopy and scanning electron microscopy showed that the mean diameter were 24.3 ± 2.6 nm, 18.2 ± 2.1 nm, and 13.6 ± 1.5 nm corresponding to the different generation hyperbranched poly(amine‐ester), and the synthesized gold nanoparticles were almost monodisperse with a narrow size distribution. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Analysis of the contrast in icosahedral gold nanoparticles

When observing nanoparticles with the transmission electron microscope very often we observe a contrast that can be interpreted at first sight as coming from a some kind of a quasicrystalline array, i.e. with order but not periodicity. In the case of icosahedral particles their structure has been well studied by many years and their contrast explained in terms of twins. In this work we present the analysis of the quasi-periodic contrast observed in icosahedral gold nanoparticles along the five-fold direction, which resembles the contrasts of a quasicrystalline structures. A detailed analysis led us to demonstrate that it could correspond to a Moiré-pattern artifact produced in an array of Mackay icosahedra. Dedicated to Professor Konrad Hayek.     

Methanol oxidation on gold nanoparticles in alkaline media: Unusual electrocatalytic activity

Methanol oxidation on gold nanoparticles has been studied using cyclic voltammetry in alkaline media. The onset for methanol oxidation in 0.1 M NaOH solutions is at ca. 0.3 V (RHE) and the currents reach a maximum value at 0.8 V. In 1 M NaOH solutions, oxidation currents are measured at potentials as low as 0.1 V. Although the currents are significantly smaller than the expected limiting diffusion current for methanol oxidation, oxidation currents are partially controlled by diffusion, as revealed by rotating disk experiments. This suggests that only a small fraction of the nanoparticles is active for the oxidation. It is proposed that formate is the final product of the oxidation and formaldehyde is an active intermediate in the process.     

金纳米粒子在毛细管电泳中的应用进展

对近年来金纳米粒子作为毛细管电色谱开管柱、整体柱和电泳微芯片固定相及缓冲溶液添加剂的应用进行了综述,并对该研究领域未来的发展方向进行展望,包括设计开发新型杂化材料、结合多种毛细管柱制备技术及深入进行相关机理研究等,为该领域今后的相关研究提供借鉴和依据。     

Plasmonic device based on a PAAm hydrogel/gold nanoparticles composite

Stimuli‐resposive hydrogels, such as poly(acrylamide), are smart materials that can be loaded with gold nanoparticles to explore the localized surface plasmon resonance effect to develop an optical device. Here we used electropolymerized poly(acrylamide) hydrogel for entrapped gold nanoparticles into gel structure (composite) to prepare a plasmonic device. Sensing tests were performed; for this bovine serum albumin molecules were placed into the composite by diffusion from an aqueous solution. The presence of the molecules alters the refractive index around the gold nanoparticles, changing its resonance conditions. The plasmonic band shifted ～3.8 nm when the composite was incubated at the 20 µg/mL bovine serum albumin solution, which is a result comparable to reports elsewhere using gold nanoparticles on glass substrates. The device showed that it was possible to detect significantly low concentrations up to 10 ng/mL of protein in aqueous solution. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42449.