金纳米颗粒在不同包裹介质中的超快等离子体动力学

Herein, we prepared four samples, namely gold/poly(sodium-p-styrenesulfonate) (Au/PSS), gold/silicon dioxide (Au/SiO₂), gold/titanium dioxide (Au/TiO₂), and gold/cuprous oxide (Au/Cu₂O) core/shell nanocomposites, to investigate how the surrounding medium affects the ultrafast plasmon dynamics of Au nanoparticles (NPs). We recorded femtosecond transient absorption spectra of Au NPs in Au/PSS, Au/SiO₂, Au/TiO₂, and Au/Cu₂O core/shell nanocomposites at various time delays. We found that the spectral features in the femtosecond transient absorption spectra of Au NPs in Au/TiO₂ and Au/Cu₂O core/shell nanocomposites were dramatically different from those of Au NPs in Au/PSS and Au/SiO₂ core/shell nanocomposites. A comprehensive analysis of the ultrafast plasmon dynamics of Au NPs in the core/shell nanocomposites revealed that following excitation of the resonance plasmon band of Au NPs, the exited electrons could be efficiently transferred into the conduction bands of TiO₂ and Cu₂O in Au/TiO₂ and Au/Cu₂O core/shell nanocomposites.     

Control of stripelike and hexagonal self-assembly of gold nanoparticles by the tuning of interactions between triphenylene ligands

We describe the self-assembly of gold nanoparticles (Au NPs) protected with newly synthesized discotic liquid crystalline molecules of hexaalkoxy-substituted triphenylene (TP) in mixed toluene/methanol solvent. The stripelike (i.e., 2D consisting of linear 1D in stripe) self-assembly is realized successfully by the aid of pi-pi stacking of TP ligand on Au NPs. The smaller Au NPs with TP (AuTP) or the longer alkyl chain between TP and the gold core provide more free spaces among TP moieties. These spaces allow easy insertion of TP on adjacent AuTPs to lead an interparticle pi-pi interaction to form the stripelike arrangement. The solvent hydrophilicity can also serve as a controlled index to tune arrangement among stripelike, hexagonal close packed (hcp), or disorder. We have changed the solvent hydrophilicity by changing the ratio of methanol to toluene, which affects the balance of solution of AuTP (in toluene) and deposition (in methanol). The larger space between TPs and appropriate solvent hydrophilicity realize stripelike self-assembly caused by a strong pi-pi interaction between TPs, which was characterized by TEM, as well as fluorescence, dynamic light scattering, and 1H NMR spectra.     

The preparation of di-t-butyl ditelluride and di-t-butyl telluride and the 125te NMR and Mössbauer spectra of some dialkyl tellurides and ditellurides

The synthesis of di-t-butyl ditelluride, t-Bu₂Te₂, and di-t-butyl telluride, t-Bu₂Te, are reported together with that of di-(neo-hexyl) ditelluride. New syntheses of Me₂Te₂ and i-Pr₂Te₂ are presented. The high resolution ¹²⁵Te NMR data and the Mössbauer data for these compounds are discussed. The use of tellurium-proton couplings in high resolution ¹²⁵Te NMR spectra in assigning the resonances in mixed dialkyl ditellurides is also illustrated.     

Biosynthesis of gold nanoparticles using Pseudomonas aeruginosa

Pseudomonas aeruginosa were used for extra-cellular biosynthesis of gold nanoparticles (Au NPs). Consequently, Au NPs were formed due to reduction of gold ion by bacterial cell supernatant of P. aeruginosa ATCC 90271, P. aeruginosa (2) and P. aeruginosa (1). The UV-vis and fluorescence spectra of the bacterial as well as chemical prepared Au NPs were recorded. Transmission electron microscopy (TEM) micrograph showed the formation of well-dispersed gold nanoparticles in the range of 15-30 nm. The process of reduction being extra-cellular and may lead to the development of an easy bioprocess for synthesis of Au NPs.     

电化学和紫外-可见吸收光谱法研究pH和金纳米粒子对细胞色素c的影响

制备了粒径均匀、平均粒子尺度为(4.7±0.6)nm,表面修饰3-巯基丙酸(MPA)的金纳米粒子(AuNPs).利用电化学和紫外-可见(UV-Vis)吸收光谱研究了pH和AuNPs对细胞色素c(Cytc)结构的影响.UV-Vis吸收光谱结果表明,pH为7.5-3.0时,Cytc和Cytc-AuNPs复合物的结构没有发生明显变化.当pH=2.0时,Cytc和Cytc-AuNPs复合物的Soret谱峰位置均发生明显移动,说明pH诱导其构象发生变化.循环伏安(CV)结果表明,表面修饰了MPA的AuNPs能促进Cytc和电极之间的电子传输,与修饰了柠檬酸根的AuNPs相比,其生物兼容性更好.pH的变化会引起CV中Cytc峰电流的改变和峰电位的移动.随着pH值的降低,Cytc电活性的量逐渐减小,并且pH诱导Cytc发生不可逆变性.AuNPs的引入使自由态的Cytc耐酸性增强,而使得吸附态的Cytc耐酸能力减弱.     

Preparation of gold-tellurium hybrid nanomaterials for surface-enhanced Raman spectroscopy

We report a simple method for preparing three different SERS-active substrates. Concentrated hydrazine solution as the reducing agent and tellurium dioxide as the precursor were used to prepare Te nanowires (NWs). The as-prepared Te NWs have an average length of 547.7 +/- 111.6 nm and an average width of 15.1 +/- 2.7 nm. Through the reaction of Te NWs with sodium tetrachloroaurate in the presence of hexadecyltrimethylammonium bromide (CTAB) over reaction times of 10, 20, and 60 min, gold-tellurium nanodumbbells, gold-tellurium nanopeapods, and gold pearl-necklace nanomaterials (Au PNNs) were obtained, respectively. By controlling the reaction time, the distance between adjacent gold nanoparticles (Au NPs) in each Te nanowire was tunable, allowing us to investigate its effect on the SERS signals. Having shorter distances among Au NPs (greater electromagnetic fields), the Au PNNs provided a reproducible enhancement factor of 5.6 x 10(9).     

Gold nanoparticles with perfluorothiolate ligands

Two syntheses of gold nanoparticles with fluorinated alkyl and aryl thiolate ligands are reported. The fluorous Au nanoparticles are smaller than previous gold fluor-capped examples, and are in the 44-75 Au atom size range. Fluoroalkyl thiolate-protected (1H,1H,2H,2H-perfluorodecanethiolate) nanoparticles synthesized by a Brust reaction are a mixture of (mainly) approximately 8.5 kDa (ca. 44 core atoms) and approximately 14 kDa (ca. 75 core atoms) species, by MALDI-mass spectrometry. This composition is consistent with thermogravimetric analysis (TGA) results of the ligand shell composition. 19F NMR spectra display a progressive line broadening of resonances for fluorine sites closer to the Au core. A second synthetic route used a (ligand replacement) reaction of pentafluorobenzenethiol with Au55(PPh3)12Cl6. The exchange is (as previously observed for nonfluorinated thiols) accompanied by nanoparticle core size changes to produce a polydisperse mixture within which a Au75 core species could be electrochemically discerned by its characteristic 0.74 V electrochemical energy gap. Further characterization of the polydisperse nanoparticle product was done by HPLC, TEM, TGA, optical spectroscopy, and NMR data. Both varieties of fluorous nanoparticles exhibit solubilities typical of perfluorinated materials, as opposed to proteo versions.     

Ligand heterogeneity on monolayer-protected gold clusters

This paper describes the effects of oxidative electronic charging of the Au cores of the monolayer-protected clusters (MPCs), Au140(S(CH2)5CH3)53 and Au38(SCH2CH2Ph)24, on nuclear magnetic resonance (NMR) spectra of their monolayer ligand shells. Previously unresolved fine structure in the 13C NMR hexanethiolate methyl and C5 methylene resonances is seen in spectra of solutions of monodisperse Au140(S(CH2)5CH3)53 MPCs, reflecting magnetically inequivalent ligand sites. Incremented increases in positive cluster core charge, effected by electrochemical charging, cause the spectral fine structure of the methyl resonance to coalesce, becoming a single peak at the Au140(3+) charge state. The spectral changes are reversible; charging back to the original core charge state regenerates the methyl 13C resonance fine structure. Adding an equimolar quantity of a Au(I) thiolate complex, Au(I)[SCH2(C6H4)C(CH3)3], to an uncharged Au140(S(CH2)5CH3)53 MPC solution in d2-methylene chloride causes partial spectral coalescence. 13C NMR spectra of Au38(SCH2CH2Ph)24 MPCs exhibit roughly comparable spectral changes upon positive core charging to the '0', '+1', and '+2' states. The NMR results indicate that exchange between magnetically inequivalent sites occurs at rates of 100 to 400 s(-1), a rate believed to be too fast to be accountable by actual exchanges of ligands between different sites on the Au core. We also describe changes in core electronic spectra of Au140(S(CH2)5CH3)53 induced by positive charging, measured using spectroelectrochemistry.     

A Xyloside-Based Ligand to Stabilize Gold Nanoparticles: Preparation and Application

Water-soluble and air-stable gold nanoparticles stabilized by a xyloside-based ligand containing a pyridine ring-functionalized 1,2,3-triazole backbone were prepared in the presence of a reducing agent. During their preparation, UV-vis and NMR spectroscopic techniques were used to study the interaction between the xyloside ligand and Au(III) ions. These AuNPs were characterized by UV-vis spectroscopy, TEM and DLS and showed a small size (average diameter<10 nm determined by TEM). Their catalytic activity was tested in the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) in water.     

Alkyl chain conformation and the electronic structure of octyl heavy chalcogenolate monolayers adsorbed on Au(111)

Adsorption states of dioctyl dichalcogenides (dioctyl disulfide, dioctyl diselenide, and dioctyl ditelluride) arranged on Au(111) have been studied by X-ray photoelectron spectroscopy (XPS), infrared-visible sum-frequency generation (SFG), and ultraviolet photoelectron spectroscopy (UPS). XPS measurements suggest that dioctyl dichalcogenides dissociatively adsorbed on Au(111) surfaces to form the corresponding monolayers having chalcogen-gold covalent bonds. The elemental compositions of octanechalcogenolates on Au(111) indicate that the saturation coverages of the octyl heavy chalcogenolate (OcSe, OcTe) monolayers are lower than that of the octanethiolate (OcS) self-assembled monolayers (SAMs). The SFG observations of the CH(2) vibrational bands for the heavy chalcogenolate monolayers strongly suggest that a discernible amount of gauche conformation exists in the monolayers, while OcS SAMs adopt highly ordered all-trans conformation. The intensity ratio of the symmetric and asymmetric CH(3) stretching vibration modes measured by SFG shows that the average tilt angle of the methyl group of the OcSe monolayers is greater than that of the OcS SAMs. The larger tilt angle of the methyl group and the existence of a discernible amount of gauche conformation in the OcSe monolayers are due to the lower surface coverage of the OcSe monolayers compared with the OcS SAMs. The smaller polarization dependence in the angle-resolved UPS (ARUPS) spectra of the OcSe monolayers than that of the OcS SAMs is caused by the more disordered structures of the alkyl chain in the former. XPS, SFG, and ARUPS measurements indicate a similar tendency for the OcTe monolayers. The density of states (DOS) observed by UPS at around 1.3 eV for OcS adsorbed on Au(111) is considered to be the antibonding state of the Au-sulfur bond. Similar DOS is also observed by UPS at around 1.0 eV for the OcSe monolayers and at approximately 1.6 eV for the OcTe monolayers on Au(111).     

Template synthesis of subnanometer gold clusters in interfacially cross-linked reverse micelles mediated by confined counterions

A cationic surfactant with a triallylammonium headgroup was cross-linked photochemically in the presence of a hydrophilic dithiol in the reverse micelle (RM) configuration. The interfacially cross-linked reverse micelles (ICRMs) are unusual templates for nanomaterials synthesis. Our previous work indicated that the ICRMs could extract anionic metal salts such as tetracholoroaurate into the hydrophilic interior, and the entrapped aurate was reduced without externally added reducing agent to form subnanometer luminescent gold clusters [Zhang, S.; Zhao, Y. ACS Nano 2011, 5, 2637-2646]. In this work, the bromide counterions were established as the reducing agent in the template synthesis. The reduction of tetrachloroaurate was proposed to happen through ligand exchange on the aurate by the bromide ions, reductive elimination of halogen, and disproportionation of the Au(I) intermediate. The size of the gold clusters could be tuned rationally by the water-to-surfactant ratio (W(0)) and the reducing agent. Monodisperse Au(4) and Au(9-10) clusters as well as larger Au(18) and Au(23) clusters were obtained from the ICRM templates. The as-prepared, metastable gold clusters were subject to reconstruction triggered by ligand exchange on the surface but could be stabilized through proper surface protection using a chelating dithiol.     

Wavelength Dependence of the Fluorescence Quenching Efficiency of Nearby Dyes by Gold Nanoclusters and Nanoparticles: The Roles of Spectral Overlap and Particle Size

The efficiency of the glutathione monolayer-protected gold nanocluster (NC) Au(25) (1.2 nm metal core diameter (d)) in quenching the emission of dyes intercalated into DNA is compared to that of 2 and 4 nm gold nanoparticles (NPs). In all cases, the DNA/dye moieties and the gold particles are not covalently attached but rather form non-covalent ground state complexes. Under these conditions, steady-state measurements reveal that the quenching efficiency of Au(25) is a factor of 10 lower than that of plasmonic 4 nm gold NPs but comparable to that of 2 nm particles which do not show a distinct plasmon band. Nonetheless, significant emission quenching is observed even at very low (nM) concentrations of Au(25). The quenching efficiency of the 4 nm NPs is significantly higher for dyes emitting near the wavelength of the plasmon peak whereas that of the 2 nm gold NPs is well described by the nano-surface energy transfer (NSET) model proposed by the Strouse group (J. Am. Chem. Soc. 127, 3115 2005). Interestingly, for Au(25) the maximum quenching efficiency occurs for dyes emitting in the same wavelength range as that of the 2 and 4 nm NPs (490-560 nm), where it shows no discrete absorption features, rather than for wavelengths coincident with its HOMO-LUMO, intra-band or inter-band transitions. The fluorescence quenching properties of Au(25) NCs are therefore found to be distinct from those of larger NCs and NPs but do not appear to conform to theoretical predictions advanced thus far.     

Coordination-based gold nanoparticle layers

Gold nanoparticle (NP) mono- and multilayers were constructed on gold surfaces using coordination chemistry. Hydrophilic Au NPs (6.4 nm average core diameter), capped with a monolayer of 6-mercaptohexanol, were modified by partial substitution of bishydroxamic acid disulfide ligand molecules into their capping layer. A monolayer of the ligand-modified Au NPs was assembled via coordination with Zr4+ ions onto a semitransparent Au substrate (15 nm Au, evaporated on silanized glass and annealed) precoated with a self-assembled monolayer of the bishydroxamate disulfide ligand. Layer-by-layer construction of NP multilayers was achieved by alternate binding of Zr4+ ions and ligand-modified NPs onto the first NP layer. Characterization by atomic force microscopy (AFM), ellipsometry, wettability, transmission UV-vis spectroscopy, and cross-sectional transmission electron microscopy showed regular growth of NP layers, with a similar NP density in successive layers and gradually increased roughness. The use of coordination chemistry enables convenient step-by-step assembly of different ligand-possessing components to obtain elaborate structures. This is demonstrated by introducing nanometer-scale vertical spacing between a NP layer and the gold surface, using a coordination-based organic multilayer. Electrical characterization of the NP films was carried out using conductive AFM, emphasizing the barrier properties of the organic spacer multilayer. The results exhibit the potential of coordination self-assembly in achieving highly controlled composite nanostructures comprising molecules, NPs, and other ligand-derivatized components.     

Amphiphilic gold nanoparticles with V-shaped arms

Here we describe a very efficient method to produce well-defined amphiphilic gold nanoparticles (Au NPs) with an equal number of hydrophobic and hydrophilic arms which are distributed along the surface of a 2-nm gold core in an alternating fashion. The strategy involves direct coupling of V-shaped block copolymer amphiphile 2 with a carboxylic group at its junction point to mercaptophenol-terminated Au NPs. The reaction proceeds under mild esterification conditions and yields the product with a molecular weight of 40 kDa, high grafting density (2.9 chains/nm2), and extremely low polydispersity (1.07). The big advantage of this approach is the opportunity to avoid the use of expensive and often inaccessible polymeric thiols. The method described here is applicable to any carboxyl-terminated molecules and can be used for the preparation of complex, yet well-defined, macromolecular hybrid structures such as 1 (Au(PB-PEG)n). The new product, which was characterized by a combination of SEC, NMR, UV-vis, DLS, and TEM, represents a unique example of gold nanoparticles soluble in any conventional solvent.     

Amine‐Functionalized Polyglycidyl Methacrylate Microsphere as a Unified Template for the Synthesis of Gold Nanoparticles and Single‐Crystal Gold Plates

Polyglycidyl methacrylate (PGMA) microspheres, crosslinked and surface‐functionalized by amine, can be used as a solid‐state template for the synthesis of gold (Au) crystals in the forms of either nanoparticles (NPs) or plates. It is discovered that the polymer microsphere acts as an internal template to cultivate Au NPs inside the microsphere or an external template to generate the single‐crystal plates depending on the critical concentration (C_cr) of gold ions. The ion–dipole interaction and the structure‐dependent solubility of gold induce two distinct gold nanostructures in the presence of the functionalized polymer microspheres. The catalytic activity and long‐term storage of the developed gold nanostructures that can be easily scaled‐up for mass production through the developed novel methodology is demonstrated.     

Gold nanoparticles stabilized by thioether dendrimers

Ligand-stabilized gold nanoparticles (Au NPs) are promising materials for nanotechnology with applications in electronics, catalysis, and sensors. These applications depend on the ability to synthesize stable and monodisperse NPs. Herein, the design and synthesis of two series of dendritic thioether ligands and their ability to stabilize Au NPs is presented. The dendrimers have 1,3,5-trisubstituted benzene branching units bridged by either meta-xylene or ethylene moieties. A comparison between the two ligands shows how both size control and the stability of the NPs are influenced by the nature of the ligand-NP wrapping interaction. The meta-xylene-bridged ligands provided NPs with a narrow size distribution centered around a diameter of 1.2 nm, whereas the NPs formed with ethylene-bridged dendrimers lack long-term stability with NP aggregation detected by UV/Vis spectroscopy and transmission electron microscopy. The bulkier tert-butyl-functionalized meta-xylene bridges form larger ligand shells that inhibit further growth of the NPs and thus provide a simple route to stable and monodisperse Au NPs that may find use as functional components in nanoelectronic devices.     

Synthesis, characterization, and self-assembly of protein lysozyme monolayer-stabilized gold nanoparticles

Lysozyme monolayer-protected gold nanoparticles (Au NPs) which are hydrophilic and biocompatible and show excellent colloidal stability (at low temperature, ca. 4 degrees C), were synthesized in aqueous medium by chemical reduction of HAuCl4 with NaBH4 in the presence of a familiar small enzyme, lysozyme. UV-vis spectra, transmission electron microscopy (TEM), atomic force microscopy, and X-ray photoelectron spectroscopy characterization of the as-prepared nanoparticles revealed the formation of well-dispersed Au NPs of ca. 2 nm diameter. Moreover, the color change of the Au NP solution as well as UV-vis spectroscopy and TEM measurements have also demonstrated the occurrence of Ostwald ripening of the nanoparticles at low temperature. Further characterization with Fourier transform infrared spectroscopy (FTIR) and dynamic light scattering indicated the formation of a monolayer of lysozyme molecules on the particle surface. FTIR data also indicated the intactness of the protein molecules coated on Au NPs. All the characterization results showed that the monodisperse Au NPs are well-coated directly with lysozyme. Driven by the dipole-dipole attraction, the protein-stabilized Au NPs self-assembled into network structures and nanowires upon aging under ambient temperature. On the basis of their excellent colloidal stability, controlled self-assembly ability, and biocompatible surface, the lysozyme monolayer-stabilized Au NPs hold great promise for being used in nanoscience and biomedical applications.     

Gold complexes containing organoselenium and organotellurium ligands

This article reviews the synthesis, structures, reactions and spectroscopic studies of gold complexes containing organoselenium and organotellurium ligands, i.e. compounds containing an Au–Se–C and Au–Te–C unit. The literature up to June 2009 has been covered. Appendix 1 lists important structural data of complexes which have been characterised by X-ray diffraction, whilst Appendix 2 contains a compilation of ⁷⁷Se and ¹²⁵Te NMR data for these compounds.     

Water-soluble gold nanoparticles protected by fluorinated amphiphilic thiolates

The preparation and the properties of gold nanoparticles (Au NPs) protected by perfluorinated amphiphiles are described. The thiols were devised to form a perfluorinated region close to the gold surface and to have a hydrophilic portion in contact with the bulk solvent to impart solubility in water. The monolayer protected clusters were prepared, in an homogeneous phase using sodium thiolates because of the low nucleophilicity of the alpha-perfluorinated thiols, and fully characterized with (1)H, (19)F NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Au NPs with core diameters ranging from 1.6 to 2.9 nm, depending on the reaction conditions, were obtained. Water-soluble NPs (MPC-F8-PEGs) were obtained with the thiol HS-F8-PEG ending with a short poly(ethylene glycol) unit (PEG-OMe 550), whereas thiols with shorter PEG chains give rise to NPs insoluble in water. MPC-F8-PEGs undergo an exchange reaction with amphiphilic alkyl thiols. ESR investigations, using a hydrophobic radical probe, indicate that the MPC-F8-PEG monolayer shows a greater hydrophobicity compared to the analogous hydrogenated monolayer.     

Electrochemically controlled assembly and logic gates operations of gold nanoparticle arrays

The reversible assembly of β-cyclodextrin-functionalized gold NPs (β-CD Au NPs) is studied on mixed self-assembled monolayer (SAM), formed by coadsorption of redox-active ferrocenylalkylthiols and n-alkanethiols on gold surfaces. The surface coverage and spatial distribution of the β-CD Au NPs monolayer on the gold substrate are tuned by the self-assembled monolayer composition. The binding and release of β-CD Au NPs to and from the SAMs modified surface are followed by surface plasmon resonance (SPR) spectroscopy. The redox state of the tethered ferrocene in binary SAMs controls the formation of the supramolecular interaction between ferrocene moieties and β-CD-capped Au NPs. As a result, the potential-induced uptake and release of β-CD Au NPs to and from the surface is accomplished. The competitive binding of β-CD Au NPs with guest molecules in solution shifted the equilibrium of the complexation-decomplexation process involving the supramolecular interaction with the Fc-functionalized surface. The dual controlled assembly of β-CD Au NPs on the surface enabled to use two stimuli as inputs for logic gate activation; the coupling between the localized surface plasmon, associated with the Au NP, and the surface plasmon wave, associated with the thin metal surface, is implemented as readout signal for "AND" logic gate operations.