pH敏感的金纳米颗粒的制备及表征

利用立方硅氧烷(odaaps)作为保护剂合成了金纳米颗粒,利用紫外-可见(UV-vis)吸收光谱、透射电镜(TEM)对纳米颗粒进行了表征。通过改变纳米溶胶的pH值,从而改变立方硅氧烷上羧基的存在形式,控制纳米颗粒表面的电荷,实现金纳米颗粒的可逆聚集与分散;当将其pH值降低至2.5时,颗粒能够完全沉淀,加碱调节其pH与原始值(pH=9)一致时,聚集的颗粒会自动重新分散形成溶胶,其具有与起始一致的高分散性。     

Local structural characterization of Au/Pt bimetallic nanoparticles

In this study, we examined the amount-dependent change in morphology for a series of Au/Pt bimetallic nanoparticles synthesized using chemical reduction. The Au/Pt molar ratio was varied from 1/1 to 1/4 to synthesize Pt shell layers with different thicknesses. We have obtained that these bimetallic nanoparticles can form flower-like nanoparticles. Moreover, an extended X-ray absorption fine structure (EXAFS) analysis was used to demonstrate the structure of Au/Pt bimetallic nanoparticles. The EXAFS results confirmed the formation of a core–shell structure and inter-diffusion between Au and Pt atoms. The composition of the shell layer was found to be Pt-enriched Au/Pt alloy.     

Pt/Au双金属纳米粒子的制备及表征

Poly (N-vinyl-2-pyrrolidone)-protected Pt/Au bimetallic nanoparticles were obtained by reducing the mixture of HAuCl4 and H2PtCl6 with sodium borohydride. UV-vis spectra, transmission electronic microscopy and X-my diffraction reveal that the prepared bimetallic nanoparticles are of alloy structure.     

二维金纳米粒子结构的制备及影响因素

用电泳沉积方法制备了金纳米粒子的二维排列结构。研究了电场强度、沉积时间、溶胶浓度、温度和方波脉冲等对沉积结构的影响。提高外加电场强度和旋加方波脉冲可以提高金粒子结构的有序性。粒子浓度减小,温度升高不利于粒子的电泳沉积。     

Gas-phase experiments on Au(III) photochemistry

Irradiation of AuCl(4)(-) and AuCl(2)(OH)(2)(-) in the gas-phase using ultraviolet light (220-415 nm) leads to their dissociation. Observed fragment ions for AuCl(4)(-) are AuCl(3)(-) and AuCl(2)(-) and for AuCl(2)(OH)(2)(-) are AuCl(2)(-) and AuClOH(-). All fragment channels correspond to photoreduction of the gold atom to either Au(II) or Au(I) depending on the number of neutral ligands lost. Fragment branching ratios of AuCl(4)(-) are observed to be highly energy dependent and can be explained by comparison of the experimental data to calculated threshold energies obtained using density functional theory. The main observed spectral features are attributed to ligand-to-metal charge transfer transitions. These results are discussed in the context of the molecular-level mechanisms of Au(III) photochemistry.     

Synthesis and characterization of Au102(p-MBA)44 nanoparticles

The synthesis of Au(102)(p-MBA)(44) nanoparticles on a preparative scale in high yield is described. Various analytical methods are shown to give results consistent with the composition and known structure of the particles, showing the preparation is essentially homogeneous, and attesting to the validity of the methods as well. Derivatization of the particles with proteins and DNA is demonstrated, and conditions are described for imaging individual particles by cryo-EM at low electron dose, close to focus, conditions optimal for recording high-resolution details.     

Facile preparation and characterization of highly antimicrobial colloid Ag or Au nanoparticles

A series of colloid silver or gold nanoparticles (AgNPs or AuNPs) were successfully prepared by in situ reduction and stabilization of hyperbranched poly(amidoamine) with terminal dimethylamine groups (HPAMAM-N(CH(3))(2)) in water, and they all exhibited highly antimicrobial activity. The particle size could be controlled easily by adjusting the molar ratio of N/Ag (or N/Au) in feed. When the molar ratio was 2, some aggregates of the nanoparticles separated from the colloidal solution, which showed some limited antimicrobial activity with the bacterial inhibition ratio of below 15%. As the molar ratio increased from 10 to 30, the average particle diameters decreased (from ca. 7.1 to 1.0 nm for AgNPs and from ca. 7.7 to 3.9 nm for AuNPs, respectively) and they all showed high dispersion stability and excellent antimicrobial efficiency. All the bacterial inhibition ratios reached up to ca. 98% at the low silver content of ca. 2.0 microg/mL or at the low gold content of ca. 2.8 microg/mL. The AgNPs or AuNPs with smaller particle size can provide much more effective contact surface with the bacteria, thus enhancing their antimicrobial efficiency. Besides, the cationic HPAMAM-N(CH(3))(2) can also do some contribution to the antimicrobial activity through the strong ionic interaction with the bacteria.     

Shell cross-linked Au nanoparticles

The organic layer of thiol-protected Au nanoparticles (ca.3 nm in diameter) was cross-linked using ring-opening metathesis polymerization or Michael addition of polyfunctional amines. The shell cross-linked nanoparticles showed increased stability toward thermal treatment and oxidative etching. The Au core of cross-linked nanoparticles was removed in an attempt to prepare hollow capsules. However, Au etching resulted in insoluble materials.     

XPS characterization of Au (Core)/SiO2 (shell) nanoparticles

Core-shell nanoparticles with ca. 15-nm gold core and 6-nm silica shell were prepared and characterized by XPS. The Au/Si atomic ratio determined by XPS is independent of the electron takeoff angle because of the concentric spherical shape of the nanoparticles. The formula given by Wertheim and DiCenzo (Phys. Rev. B 1988, 37, 844) for spherical nanoparticles and the modified one by Yang et. al. (J. Appl. Phys. 2005, 97, 024303) for core-shell nanoparticles are used to correlate the XPS-derived composition with the geometry of the nanoparticles only after significantly modifying either the bulk density of the silica shell or the attenuation length of the photoelectrons.     

Synthesis and characterization of Au and Ag nanoparticles protected by PAMAM and its derivative

1,8-naphthalimide-labelled polyamidoamine dendrimer (PAMAM-N) was synthesized and used to stabilize Au and Ag nanoparticles, which were characterized by UV-Vis absorption and fluorescence spectroscopies, and transmission electron microscopy. The dimensions of Au and Ag nanoparticles protected by PAMAM-N were smaller and the size distribution was narrower when compared to those of polyamidoamine dendrimer. The presence of chromophore fragment (1,8-naphthalimide) allowed the fluorescent labeling of Au and Ag nanoparticles.     

Micropatterns constructed from Au nanoparticles

Covalently linked Au-NPs micropatterns have been successfully fabricated from the self-assembly film composed of 4-mercaptophenol-capped Au nanoparticles (Au-NPs) and -N2+ containing polymers of nitro-diazoresin (NDR) by selective exposure to UV light and development in sodium dodecyl sulfate (SDS) aqueous solution. The resultant well-defined micropatterns were characterized with AFM and XPS.     

Phase-resolved detection in ion-mobility spectrometry

Throughput has been improved in an ion-mobility spectrometer by means of continuous ion-beam modulation and phase-resolved detection. Conventional ion-mobility spectrometry (IMS) utilizes brief packets of ions for separation in the gas phase. In contrast, this preliminary report outlines a new detection method based on phase resolution and involves monitoring the ion signal continuously, which raises the duty cycle of the instrument from approximately 1% (conventional IMS) to 50%. The greater duty cycle is shown to improve signal-to-noise ratios (S/N). However, the higher S/N levels did not translate into higher sensitivity values when calibration plots were constructed. It is demonstrated that even analytes with small differences in drift times can be modulated at frequencies that maximize the measured phase differences between ions. Phase-resolved signals can be processed with a Fourier transform and chemometric data reduction to simplify identification of the analyte from its phase spectra.     

Designing caps for colloidal Au nanoparticles

The plasmonic property of a nanostructure is highly dependent on its morphology, but there are few methods for appending a domain as the “functional group” or modifier. As a means of modulating plasmonic properties, we create and modulate Au hats on Au nanoparticles, including mortarboards, beret hats, helmets, crowns, antler hats and antenna hats. The structural control arises from the active surface growth as a result of dynamic competition between ligand absorption and metal deposition. It allows the continuous tuning of hat morphologies, from the facet-controlled growth of mortarboards, to the spreading-favored growth of beret hats and helmets, and to the vertical growth of pillars in crowns, antler hats and antenna hats. Among these plasmonic nanostructures, the mortarboards show excellent SERS enhancement of 8.1 × 10⁵, which is among the best in colloidal nanostructures; and the antler hats show the photothermal conversion efficiency of 66.2%, which compares favorably with the literature reports.

We show that active surface growth is an effective method to create structural variety in the appending domain of Au seeds. The dynamic competition between the growth sites led to different Au hats on seeds.     

DNA-embedded Au/Ag core-shell nanoparticles

Here, we synthesized highly stable DNA-embedded Au/Ag core-shell nanoparticles (NPs) by a straightforward silver-staining of DNA-modified Au nanoparticles (AuNPs); unlike conventional DNA-surface modified NPs that present particle stability issues, DNA-embedded core-shell NPs offer an extraordinary stability with nanoscale controllability of silver shell thickness; these DNA-embedded core-shell NPs show excellent biorecognition properties and Ag shell-thickness-based optical properties, distinctively different from those of a mixture of AuNPs and AgNPs or Ag/Au alloy nanoparticles.     

Progress on phthalocyanine-conjugated Ag and Au nanoparticles: Synthesis,characterization, and photo-physicochemical properties

Phthalocyanine (Pc) complexes are an important class of dyes with numerous (e.g., biological, photophysical, and analytical) applications. Among the methods used to improve the properties of these complexes, one should mention the introduction of different substituents, variation of the central metal ion, ligand exchange, and conjugation to nanomaterials (e.g., carbon-based nanomaterials and metal nanoparticles (NPs)). This work briefly reviews Pc complex conjugation to Ag and Au NPs, highlights the different NP shapes, and discusses the diversity of conjugation approaches. Moreover, the use of UV–Vis spectroscopy, powder X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy, atomic force microscopy, dynamic light scattering and Fourier transform infrared spectroscopy to characterize Pc-NP hybrids is summarized. The effect of conjugation on Pc photo-physicochemical properties (fluorescence, singlet oxygen generation, triplet state formation, and optical limiting behavior) is discussed, and future perspectives for the synthesis and applications of new hybrids are provided.     

Morphology dependent electrocatalytic activity of Au nanoparticles

The electrocatalytic activity of spherical shape Au particles chemically grown on a sol–gel derived 3D silicate network modified conducting surface has been studied using ascorbate as a model. The nanostructured Au particles show morphology dependent electrocatalytic activity towards ascorbate. Unusual voltammetric behavior for ascorbate has been observed. Unlike the polycrystalline Au electrode, the nanostructured electrode shows two well defined voltammetric peaks for ascorbate at 0 and 0.3 V in neutral and alkaline pHs. These voltammetric peaks are assigned for the oxidation of ascorbate to dehydroascorbate (DHA) and the further oxidation of 2,3-diketogluonic acid (DKG), the hydrolyzed product of DHA. The voltammetric peak corresponding to the oxidation of DKG is very sensitive to the supporting electrolyte anions and solution pH. Voltammetric behavior of DHA has been investigated to support the oxidation pathway of ascorbate on the nanostructured electrode. Surface morphology of the particle controls the electrocatalytic activity.     

Grignard functionalization of Weinreb amide-modified Au nanoparticles

Reactions of Grignard and organolithium reagents are staple transformations in organic chemistry. However, their use in the chemical functionalization of monolayer-protected metallic nanoparticles is unprecedented. In this letter, we report the reaction of Au nanoparticles bearing a mixed monolayer of alkanethiol ligands that are methyl- and N-methoxy- N-methyl amide-terminated. The latter of these rapidly undergoes reaction with organometallic reagents, achieving high yields (in some cases, nearly quantitative) in only a few hours without the need for high pressure, temperature or catalysts. We assess the feasibility of this reaction with a range of organometallic reagents on the basis of both surface reaction yield and also the stability of the particles (defined as the mass % Au particles recovered vs a control). Demonstrating the utility of these strong organometallic reagents opens the door to a large class of reactions that are underutilized within the field of nanomaterials.     

Electrospinning nanosuspensions loaded with passivated Au nanoparticles

Aqueous polyethylene oxide (PEO) solutions (2 MDa, 2-5 wt %) with or without citrate passivated Au nanoparticles (5.7×10⁻⁷ wt %) have been electrospun, producing fibres with diameters from 290 μm to 55 nm. The incorporation of nanoparticles suppresses the diameter of the fibres and increases the degree of crystallinity. Such nanocomposite fibres are of interest as self-assembled templates for bottom-up fabrication methodologies.