Dendrimer-encapsulated Au Nanoparticles Research Articles

Water splitting-assisted electrocatalysis based on dendrimer-encapsulated Au nanoparticles for perspiration glucose analysis

• Dendrimer-encapsulated Au nanoparticles (Au DENs) for wearable perspiration glucose analysis was achieved based on water splitting-assisted electrocatalysis. • Smaller Au DENs were found to be more electrocatalytically active toward glucose oxidation which ensures highly sensitive detection of trace glucose in perspiration. • Zwitterionically terminated dendrimer provides an anti-fouling coating of the electrocatalyst for highly selective and durable glucose monitoring. Here, we report the use of dendrimer-encapsulated Au nanoparticles (Au DENs) terminated with zwitterionic groups (G4-NH 2 -PS(Au)) for nonenzymatic perspiration glucose analysis based on water splitting-assisted electrocatalysis (WSE). The Au DENs with controllable sizes are prepared and characterized, and their electrocatalytic activities towards nonenzymatic glucose oxidation are investigated. It is found that the Au DENs with a smaller diameter (1.3 ± 0.5 nm) show higher electrocatalytic activity than larger Au DENs do (1.7 ± 0.7 nm and 2.8 ± 1.4 nm), which leads to a sensitivity of 414 μA mM −1 cm −2 for glucose detection and a detection limit of 4.9 μM. The Au DENs terminated with zwitterionic groups also exhibit acceptable selectivity, reproducibility, and long-time stability for glucose sensing in artificial perspiration samples. The sensor is then used for wearable perspiration glucose monitoring, and the results show a correlation between perspiration glucose and blood glucose.

Molecular dynamics simulations of PAMAM dendrimer-encapsulated Au nanoparticles of different sizes under different pH conditions

Molecular dynamics (MD) simulations were carried out to investigate the conformations of fourth generation polyamidoamine (G4 PAMAM) dendrimer-encapsulated Au nanoparticles (AuNPs) of different sizes at different pH conditions. The consistent valence force field (CVFF) was used to model the interaction between the atoms of G4 PAMAM dendrimer and water molecules as well as their interactions with the Au atoms of AuNP. The many-body tight-binding potential was adopted to describe the interaction between Au atoms. The simulation results show a single G4 PAMAM dendrimer can only partially cover the AuNP when its diameter is larger than 2.3nm. According to the variations of radius of gyration (Rg) values, the conformations of PAMAM dendrimers become more compact after covering the AuNP at neutral pH. According to the Stokes–Einstein (SE) relation and the diffusion coefficients obtained by the Einstein equation, it was proposed that both the PAMAM dendrimer conformation and the interaction strength between the PAMAM/AuNP and water molecules have significant influences on the diffusion behaviors of PAMAM/AuNP systems.

A Facile Strategy to Prepare Dendrimer-stabilized Gold Nanorods with Sub-10-nm Size for Efficient Photothermal Cancer Therapy.

Gold (Au) nanoparticles are promising photothermal agents with the potential of clinical translation. However, the safety concerns of Au photothermal agents including the potential toxic compositions such as silver and copper elements in their structures and the relative large size-caused retention and accumulation in the body post-treatment are still questionable. In this article, we successfully synthesized dendrimer-stabilized Au nanorods (DSAuNRs) with pure Au composition and a sub-10-nm size in length, which represented much higher photothermal effect compared with dendrimer-encapsulated Au nanoparticles due to their significantly enhanced absorption in the near-infrared region. Furthermore, glycidol-modified DSAuNRs exhibited the excellent biocompatibility and further showed the high photothermal efficiency of killing cancer cells in vitro and retarding tumor growth in vivo. The investigation depicted an optimal photothermal agent with the desirable size and safe composition.

ChemInform Abstract: Molecular Catalysis Science: Nanoparticle Synthesis and Instrument Development for Studies under Reaction Conditions

AbstractReview: 77 refs.

Catalytic Behavior of Different Sizes of Dendrimer-Encapsulated Aun Nanoparticles in the Oxidative Degradation of Morin with H2O2

Different sizes of icosahedral-like dendrimer-encapsulated Au nanoparticles (Au55- and Au147-DENs) were prepared in the presence of generation 6 amine-terminated dendrimers (G6-PAMAM-NH2) as a template. The synthesis is carried out by the complexation of a Au metal precursor (AuHCI4) with the tertiary amine groups within the dendrimer framework. The addition of excess reducing agent, NaBH4, results in the formation of Au nanoparticles encapsulated within the dendrimer cavities. The as-prepared catalysts were characterized using UV-visible (UV-vis) spectroscopy, high-resolution transmission electron microscopy (HRTEM), energy-dispersive X-ray analysis (EDX), and Fourier transform infrared (FTIR). The average sizes of Au55- and Au147-DENs were determined to be 1.7 ± 0.4 and 2.0 ± 0.3 nm, respectively. The catalytic activity of these Au-DEN catalysts was evaluated in the oxidative decomposition of morin by H2O2. Since morin has a maximum absorption band at λ 410 nm at pH 10, this catalyzed oxidation process was monitored by time-resolved UV-vis spectroscopy. The catalytic activities of these two catalysts were compared by fitting the kinetic data to the Langmuir-Hinshelwood model. This model allows the determination of adsorption constants of both morin (K(morin)) and H2O2 (K(H2O2)) on the catalyst surface. A full kinetic study for this Au-DEN-catalyzed oxidative degradation of morin is reported.

A novel PAMAM-Au nanostructure-amplified CdSe quantum dots electrochemiluminescence for ultrasensitive immunoassay

A novel PAMAM dendrimers-Au nanostructure was prepared and used to develop an amplified CdSe quantum dots (QDs) probe for ultrasensitive electrochemiluminescence (ECL) immunoassay. The unique dendrimer-encapsulated Au nanoparticles have numerous functional groups for loading enough QDs, and the ECL of QDs was enhanced by the localized surface plasmon resonance (LSPR) of gold nanoparticles (Au NPs). After the PAMAM dendrimer was used to form an effective immobilization matrix for biomolecules, the capture antibody (Ab1) was covalently conjugated to the dendrimers. In the presence of the target human IgG (Ag), the secondary antibody (Ab2) modified PAMAM-Au–CdSe QDs signal probe was attached to the electrode. On the basis of the amplified ECL signal of the CdSe QDs, an ultrasensitive signal-on ECL immunosensor was developed. The PAMAM-Au–CdSe QDs nanostructure opens a new promising material direction for ECL biosensing; this method shows considerable promise for diverse clinical applications.

Molecular catalysis science: Nanoparticle synthesis and instrument development for studies under reaction conditions

The synthesis of architecturally designed catalytic nanostructures and their in situ characterization under reaction conditions enable the development of catalysts with improved stability, reactivity, and product selectivity. Throughout this review paper, we will explore three recent reports that demonstrate the invaluable synergetic impact of combining synthesis, catalysis, and in situ spectroscopy for catalysts development. In the first example, product selectivity in 1,3 butadiene hydrogenation reaction was tuned by employing size-selected Pt nanoparticles as catalysts. SFG vibrational spectroscopy measurements uncovered the mechanism that induced the size-dependent selectivity. The important role of metal/metal-oxide interface during CO oxidation reaction is demonstrated in the second part of this review paper. In situ synchrotron-sourced X-ray spectroscopy correlated between the oxidation state of the metal-oxide support and its impact on the catalytic reactivity of supported Pt nanoparticles. In the third example, dendrimer-encapsulated Au nanoparticles were used as catalyst for cascade reactions, which were previously catalyzed by homogeneous catalysts. Reactants into product evolution and the oxidation state of catalytically active Au nanoparticles within the flow reactor were mapped with micrometer-sized IR and X-ray beams. These three examples demonstrate the important role of colloidal synthesis and in situ spectroscopy measurements for in-depth analysis of structure–reactivity correlations.

Dynamic photocatalytic hydrogen production from ethanol–water mixtures in an optical fiber honeycomb reactor loaded with Au/TiO2

Cordierite honeycombs loaded with different amounts of Au/TiO2 have been used in an optical fiber photoreactor illuminated with UV LEDs to produce hydrogen from ethanol and water–ethanol mixtures. The photoreactions have been carried out at 298–348K, volume hourly space velocities of 300–2100h−1, Au contents of 0.5–2wt.% with respect to TiO2, and ethanol molar contents of 1–100%. Excellent dispersion and homogeneous particle size of gold has been obtained by using pre-formed, dendrimer-encapsulated Au nanoparticles. The best photocatalytic performance has been obtained over monoliths loaded with ca. 0.5mgcm−2 of Au/TiO2 (1.0–1.5wt.% Au), which corresponds to a photocatalyst layer thickness of about 1μm. In gas phase, acetaldehyde adsorption onto the photocatalyst surface plays an important role in the dynamics of the photoprocess by affecting hydrogen evolution sites, which is improved with temperature and short contact times. Hydrogen photogeneration in liquid phase is significantly enhanced (fivefold increase) in the optical fiber honeycomb photoreactor with respect to a conventional slurry photoreactor.

A theoretical and experimental examination of systematic ligand-induced disorder in Au dendrimer-encapsulated nanoparticles

In this paper we present a new methodology for the analysis of 1–2 nm nanoparticles using extended X-ray absorption fine structure (EXAFS) spectroscopy. Different numbers of thiols were introduced onto the surfaces of dendrimer-encapsulated Au nanoparticles, consisting of an average of 147 atoms, to systematically tune the nanoparticle disorder. An analogous system was investigated using density functional theory molecular dynamics (DFT-MD) simulations to produce theoretical EXAFS signals that could be directly compared to the experimental results. Validation of the theoretical results by comparing to experiment allows us to infer previously unknown details of structure and dynamics of the nanoparticles. Additionally, the structural information that is learned from theoretical studies can be compared with traditional EXAFS fitting results to identify and rationalize any errors in the experimental fit. This study demonstrates that DFT-MD simulations accurately depict complex experimental systems in which we have control over nanoparticle disorder, and shows the advantages of using a combined experimental/theoretical approach over standard EXAFS fitting methodologies for determining the structural parameters of metallic nanoparticles.

Sensitive electrochemical immunosensor for α-synuclein based on dual signal amplification using PAMAM dendrimer-encapsulated Au and enhanced gold nanoparticle labels

A novel electrochemical immunosensor for sensitive detection of α-synuclein (α-SYN), a very important neuronal protein, has been developed based on dual signal amplification strategy. Herein, G4-polyamidoamine dendrimer-encapsulated Au nanoparticles (PAMAM-Au nanocomposites) were covalently bound on the poly- o-aminobenzoic acid (poly- o-ABA), which was initially electropolymerized on the electrode surface to perform abundant carboxyl groups. The formed immunosensor platform, PAMAM-Au, was proved to provide numerous amino groups to allow highly dense immobilization of antigen, and facilitate the improvement of electrochemical responses as well. Subsequently, the enhanced gold nanoparticle labels ({HRP-Ab 2-GNPs}) were fabricated by immobilizing horseradish peroxidase-secondary antibody (HRP-Ab 2) on the surface of gold nanoparticles (GNPs). After an immunoassay process, the {HRP-Ab 2-GNPs} labels were introduced onto the electrode surface, and produced an electrocatalytic response by reduction of hydrogen peroxide (H 2O 2) in the presence of enzymatically oxidized thionine. On the basis of the dual signal amplification of PAMAM-Au and {HRP-Ab 2-GNPs} labels, the designed immunosensor displayed an excellent analytical performance with high sensitivity and stability. This developed strategy was successfully proved as a simple, cost-effective method, and could be easily extended to other protein analysis schemes.

Electrochemical Synthesis and Electrocatalytic Properties of Au@Pt Dendrimer-Encapsulated Nanoparticles

Dendrimer-encapsulated Au nanoparticles comprised of an average of 147 atoms were synthesized and immobilized on a glassy carbon electrode. A one-atom-thick shell of Cu was added to the Au core by electrochemical underpotential deposition, and then this shell was replaced with Pt by galvanic exchange. The results indicate that this synthetic approach leads to well-defined core/shell nanoparticles <2 nm in diameter. The rates of oxygen reduction at the Au@Pt electrocatalysts were compared to Pt-only and Au-only, 147-atom dendrimer-encapsulated nanoparticles.