Various Au nanoparticle organizations fabricated through SiO2 monomer induced self-assembly

Selective Photocatalytic Activation of Ethanol C-H and O-H Bonds over Multi-Au@SiO2/TiO2: Role of Catalyst Surface Structure and Reaction Kinetics

The chemical bond diversity and flexible reactivity of biomass-derived ethanol make it a vital feedstock for the production of value-added chemicals but result in low conversion selectivity. Herein, composite catalysts comprising SiO₂-coated single- or multiparticle Au cores hybridized with TiO₂ nanoparticles (mono- or multi-Au@SiO₂/TiO₂, respectively) were fabricated via electrostatic self-assembly. The C-H and O-H bonds of ethanol were selectively activated (by SiO₂ and TiO₂, respectively) under irradiation to form CH₃CH^•(OH) or CH₃CH₂O^• radicals, respectively. The formation and depletion kinetics of these radicals was analyzed by electron spin resonance to reveal marked differences between mono- and multi-Au@SiO₂/TiO₂. Consequently, the selectivity of these catalysts for 1,1-diethoxyethane after 6 h irradiation was determined as 81 and 99%, respectively, which was attributed to the more pronounced effect of localized surface plasmon resonance for multi-Au@SiO₂/TiO₂. Notably, only acetaldehyde was formed on a Au/TiO₂ catalyst without a SiO₂ shell. Fourier transform infrared (FTIR) spectroscopy indicated that the C-H adsorption of ethanol was enhanced in the case of multi-Au@SiO₂/TiO₂, while NH₃ temperature-programmed desorption and pyridine adsorption FTIR spectroscopy revealed that multi-Au@SiO₂/TiO₂ exhibited enhanced surface acidity. Collectively, the results of experimental and theoretical analyses indicated that the adsorption of acetaldehyde on multi-Au@SiO₂/TiO₂ was stronger than that on Au/TiO₂, which resulted in the oxidative coupling of ethanol to afford 1,1-diethoxyethane on the former and the dehydrogenation of ethanol to acetaldehyde on the latter.

Electrochemically driven optical and SERS immunosensor for the detection of a therapeutic cardiac drug

Cardiovascular diseases pose a serious health risk and have a high mortality rate of 31% worldwide. Digoxin is the most commonly prescribed pharmaceutical preparation to cardiovascular patients particularly in developing countries. The effectiveness of the drug critically depends on its presence in the therapeutic range (0.8–2.0 ng mL⁻¹) in the patient's serum. We fabricated immunoassay chips based on QD photoluminescence (QDs-ELISA) and AuNP Surface Enhanced Raman Scattering (SERS-ELISA) phenomena to detect digoxin in the therapeutic range. Digoxin levels were monitored using digoxin antibodies conjugated to QDs and AuNPs employing the sandwich immunoassay format in both the chips. The limit of detection (LOD) achieved through QDs-ELISA and SERS-ELISA was 0.5 ng mL⁻¹ and 0.4 ng mL⁻¹, respectively. It is demonstrated that the sensitivity of QDs-ELISA was dependent on the charge transfer mechanism from the QDs to the antibody through ionic media, which was further explored using electrochemical impedance spectroscopy. We demonstrate that QDs-ELISA was relatively easy to fabricate compared to SERS-ELISA. The current study envisages replacement of conventional methodologies with small immunoassay chips using QDs and/or SERS-based tags with fast turnaround detection time as compared to conventional ELISA.

Cardiovascular diseases pose a serious health risk and have a high mortality rate of 31% worldwide.

Preparation and biomedical applications of bright robust silica nanocapsules with multiple incorporated InP/ZnS quantum dots

InP/ZnS quantum dots incorporated in silica capsules are robust and bright, and can image cells clearly.

Synthesis and Properties of Au Nanoparticles with Various Sizes

Properties of Au nanoparticles (NPs) caused by various sizes (5-12 nm) were studied in this article. Au NPs capped with citrate of various sizes were synthesized by two methods including trisodium citrate dihydrate reduction of chloroauric acid tetrahydrate and sodium borohydride reducion of chloroauric acid tetrahydrate. Au NPs were characterized and measured by using transmission electron microscope (TEM), UV-vis-NIR absorption spectroscopy, and surface Raman scattering. The results of experiment indicated that the size of Au NPs was related to the type of reducing agent and molar ratio of reducing agent and chloroauric acid. The weaker the reducing capacity of the reducing agent or the lower the molar ratio, the bigger the size of Au NPs is. The max wavelength of absorption peak for the citrate-capped Au NPs is red-shifted with the increase of particle diameter. Raman scattering observed from Au NPs of various sizes is found to be NP size-dependent. It is clear that the bigger Au NPs are more apparent in the Raman scattering determination. Size-tunable Au NPs should be crucial for biosensors, particularly as Raman-tag particles.

A combined size sorting strategy for monodisperse plasmonic nanostructures

The fabrication of highly monodisperse silica coated Au NPs by the microemulsion approach and the selection of the nanostructure morphology have been described. Several experimental conditions, synthetic parameters and post-preparative strategies such as reaction time, precursor concentration, size selection techniques and NP surface treatments have been suitably investigated in order to fabricate Au and Au@SiO2 NPs with peculiar and tuneable plasmonic properties that strongly depend on the specific size distribution and nanostructure morphology. In particular, size selected precipitation of oleylamine-capped Au NPs by antisolvent titration has successfully offered a strategy to discriminate and collect monodisperse fractions with different average size and narrow size distribution. Moreover, for the first time, a deep insight into the microemulsion mechanism for the silica shell growth has been provided, highlighting the critical role played by the density of oleylamine at the Au NP surface. Specifically the capping agent has been demonstrated to strongly determine the multiplicity of the core in the final Au@SiO2 nanostructures. Density gradient centrifugation has been finally performed to sort the achieved Au@SiO2 NPs with different morphologies, which was ultimately able to recover a significant fraction formed of two Au NPs in one silica shell. A systematic characterization of the Au and Au@SiO2 NPs has been carried out by complementary morphological and spectroscopic techniques. These deeply investigated materials, with tuneable plasmonic properties, have been proposed as versatile building blocks useful for the design and fabrication of plasmonic and photonic structures as well as metamaterials for device applications.

One-step synthesis and characterization of core-shell Fe@SiO2 nanocomposite for Cr (VI) reduction

A facile one-step method was developed to fabricate mono-dispersed Fe nanoparticles (Fe NPs) coated with SiO(2) shell by aqueous reduction method combined with modified Stöber method. Borohydride was acted not only as a reductant for iron salt but also as a catalyst for hydrolysis and polycondensation reaction of tetraethylorthosilicate (TEOS), and more importantly, there was no need to use surface primer for the generation of Fe NPs and catalyst NH(4)OH for SiO(2). Both the Fe NPs agglomeration and SiO(2) shell thickness can be controlled through the synthetic conditions. Lower potassium borohydride (KBH(4)) injection speed was preferable to assemble Fe NPs. The SiO(2) shell thickness increased gradually with the increase of TEOS amount. Under the condition of TEOS amount of 0.1mL and KBH(4) injection speed of 5mL/min, 25nm single Fe NP was coated with SiO(2) shell with thickness of about 9nm. The resulting nanoporous SiO(2) shell was proved to allow reactant to reach the Fe NPs while at the same time protect them from aggregation. The reactivity characterization of the SiO(2)-coated Fe nanoparticles (Fe@SiO(2)) showed that both TEOS concentration and KBH(4) injection speed had effect on Cr (VI) degradation ability. The highest removal capacity of Fe@SiO(2) can reach 467mgCr/gFe at an initial Cr (VI) concentration of 70mg/L under pH 6.0±0.1. XPS and TEM results showed that Cr (VI) was converted to nontoxic Cr (III) and the reaction product was completely adsorbed to SiO(2) shell.

Nanoparticle PEGylation for imaging and therapy

Nanoparticles are an essential component in the emerging field of nanomedical imaging and therapy. When deployed in vivo, these materials are typically protected from the immune system by polyethylene glycol (PEG). A wide variety of strategies to coat and characterize nanoparticles with PEG has established important trends on PEG size, shape, density, loading level, molecular weight, charge and purification. Strategies to incorporate targeting ligands are also prevalent. This article presents a background to investigators new to stealth nanoparticles, and suggests some key considerations needed prior to designing a nanoparticle PEGylation protocol and characterizing the performance features of the product.