Amphiphilic Janus Gold Nanoparticles Prepared by Interface‐Directed Self‐Assembly: Synthesis and Self‐Assembly

Materials with Janus structures are attractive for wide applications in materials science. Although extensive efforts in the synthesis of Janus particles have been reported, the synthesis of sub‐10 nm Janus nanoparticles is still challenging. Herein, the synthesis of Janus gold nanoparticles (AuNPs) based on interface‐directed self‐assembly is reported. Polystyrene (PS) colloidal particles with AuNPs on the surface were prepared by interface‐directed self‐assembly, and the colloidal particles were used as templates for the synthesis of Janus AuNPs. To prepare colloidal particles, thiol‐terminated polystyrene (PS‐SH) was dissolved in toluene and citrate‐stabilized AuNPs were dispersed in aqueous solution. Upon mixing the two solutions, PS‐SH chains were grafted to the surface of AuNPs and amphiphilic AuNPs were formed at the liquid–liquid interface. PS colloidal particles decorated with AuNPs on the surfaces were prepared by adding the emulsion to excess methanol. On the surface, AuNPs were partially embedded in the colloidal particles. The outer regions of the AuNPs were exposed to the solution and were functionalized through the grafting of atom‐transfer radical polymerization (ATRP) initiator. Poly[2‐(dimethamino)ethyl methacrylate] (PDMAEMA) on AuNPs were prepared by surface‐initiated ATRP. After centrifugation and dissolving the colloidal particles in tetrahydrofuran (THF), Janus AuNPs with PS and PDMAEMA on two hemispheres were obtained. In acidic pH, Janus AuNPs are amphiphilic and are able to emulsify oil droplets in water; in basic pH, the Janus AuNPs are hydrophobic. In mixtures of THF/methanol at a volume ratio of 1:5, the Janus AuNPs self‐assemble into bilayer structures with collapsed PS in the interiors and solvated PDMAEMA at the exteriors of the structures.     

Self-assembly and encoding of polymer-stabilized gold nanoparticles with surface-enhanced Raman reporter molecules

Polymer-stabilized gold nanoparticles (AuNPs) were prepared and encoded with a range of surface-enhanced Raman reporter molecules. A range of as-synthesized polymers produced by reversible addition fragmentation chain transfer (RAFT) polymerization were demonstrated to self-assemble at the surface of AuNPs dispersed in water. The method involved the coprecipitation of polymer-gold conjugates by the addition of polymer dissolved in a water-miscible solvent to gold AuNPs dispersed in water. This method represents a simplification of the preparation of polymer-stabilized AuNPs compared with other published methods, in that the AuNPs do not need to be first transferred to an organic solvent. The process enabled the polymer stabilized AuNPs to be easily recovered by filtration or by phase transfer of the AuNPs to an organic solvent in which the RAFT polymer was soluble. The polymer-stabilized AuNPs were characterized by a range of methods including UV-visible spectrophotometry, transmission electron microscopy, thermogravimetric analysis, dynamic light scattering, and attenuated total reflection Fourier transform infrared spectroscopy. Furthermore, 1H pulsed field gradient spin echo NMR was utilized to characterize the self-diffusion of the polymer-stabilized AuNPs. Finally, we then demonstrated that these polymer-stabilized AuNPs maintained their ability to be encoded with surface-enhanced Raman spectroscopy reporter molecules.     

Small Size Effect and Concentration Response of Gold Nanoparticles in Electrochemiluminescence Reaction

Recent reports have used gold nanoparticles (AuNPs) as a co‐reactant for the electrochemiluminescence (ECL) reaction of ruthenium complex. However, understanding the size effect of AuNPs on ECL reaction is very meaningful to explore its unknowns and develop its applications at the molecular level. In this paper, we examined the behavior of various small‐size AuNPs in ECL reaction, focusing on changes in ECL caused by AuNPs size and reasons for this change. Although the luminescence spectra and excitation potential have hardly changed in ECL reaction, the difference of ECL intensities induced by different sizes AuNPs is very obviously. Our experimental results revealed disparate behaviors depending on AuNPs size: the small‐sized AuNPs can lead to stronger ECL, and ECL intensities increase as the addition of AuNPs concentration in the wider range. This small size effect is related to an intermediate process of charge‐discharge in electric double layer formed by adsorbing ruthenium complex with AuNPs, and the surface and quantum size effect of AuNPs may affect this intermediate process. More importantly, AuNPs can act as a marker, has the same small size effect and concentration response, and bring about a promising platform for biochemical analysis.     

CHCA-modified Au nanoparticles for laser desorption ionization mass spectrometric analysis of peptides

Gold nanoparticles (AuNPs) have been studied as a potential solid-state matrix for laser desorption/ionization mass spectrometry (LDI-MS) but the efficiency in ionization remains low. In this report, AuNPs are capped by a self-assembled monolayer of cysteamine and modified with α-cyano-4-hydroxycinnanic acid (CHCA) for effective MALDI measurements. CHCA-terminated AuNPs offer marked improvement on peptide ionization compared with citrate-capped or cysteamine-capped AuNPs. The coating also effectively suppresses formation of Au cluster ions and analyte fragment ions, leading to cleaner mass spectra. Addition of glycerol and citric acid to the peptide/AuNPs sample further improves the performance of these AuNPs for LDI-MS analysis. Glycerol appears to enhance the dispersion of AuNPs in sample spots, increasing the sample ionization and shot-to-shot reproducibility, while citric acid serves as an external proton donor, providing high production of protonated analyte ions and reducing fragmentation of peptides on the nanoparticle-based surface. Optimal ratios of citric acid, glycerol, and AuNPs in sample solution have been systematically studied. A more than 10-fold increase for desorption ionization of peptides can be achieved by combining 5% glycerol and 20 mM citric acid with the CHCA-terminated AuNPs. The applicability of the CHCA-AuNPs for LDI-MS analysis of protein digests has also been demonstrated. This work shows the potential of AuNPs for SALDI-MS analysis, and the improvement with chemical functionalization, controlled dispersion, and use of an effective proton donor.     

Self-assembly of ionic liquid (BMI-PF6)-stabilized gold nanoparticles on a silicon surface: chemical and structural aspects

Ultrafine monodisperse gold nanoparticles (AuNPs) were synthesized by an elegant sputtering of gold onto 1- n-butyl-3-methylimidazolium hexafluorophosphate (BMI-PF(6)) ionic liquid. It was found that the BMI-PF(6) supramolecular aggregates were loosely coordinated to the gold nanoparticles and were replaceable with thiol molecules. The self-assembly of BMI-PF(6)-stabilized AuNPs onto a (3-mercaptopropyl)trimethoxysilane (MPS)-functionalized silicon surface in 2D arrays, followed by dodecanethiol (DDT) treatment, have been demonstrated using X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and contact angle measurements. DDT treatment of tethered AuNPs revealed two types of interactions between AuNPs and the MPS-functionalized surface: (a) AuNPs anchor through Au-S chemisorption linkage resulting in strong immobilization and (b) some of the AuNPs are supported by physisorption, driven by BMI-PF(6). The attachment of these particles remains unchanged with sonication. The replacement of BMI-PF(6) aggregates from physisorbed AuNPs with DDT molecules advances the dilution of their interaction with the MPS-functionalized surface, and they subsequently detach from the silicon surface. The present finding is promising for the immobilization of ionic liquid-stabilized nanoparticles, which is very desirable for electronic and catalytic device fabrication. Additionally, these environmentally friendly AuNPs are expected to replace conventional citrate-stabilized AuNPs.     

用金纳米粒子修饰硅纳米线及复合结构的光谱性质研究

在溶液中以正己硫醇作稳定剂, 利用HAuCl4与HF处理后的硅纳米线(SiNWs)的氧化还原反应, 在SiNWs表面负载金纳米粒子(AuNPs). 通过调整HAuCl4的浓度, 得到了AuNPs粒径从3.2到7.0 nm的AuNPs/SiNWs复合结构, 并对这种复合结构进行了紫外-可见吸收光谱和荧光光谱研究. 紫外-可见吸收光谱研究表明, 负载不同粒径的AuNPs的SiNWs在530～580 nm间有明显的由AuNPs表面等离子体共振引起的吸收, 且随着AuNPs粒径的增加, 该吸收峰发生红移. 负载前后的荧光光谱表明, 在红光和绿光区负载AuNPs的SiNWs的荧光峰与HF处理后SiNWs的荧光峰峰形相当, 峰位变化不大; 但在蓝光区, 不同于HF处理前后SiNWs的发射峰(464 nm左右), 负载了AuNPs的SiNWs在423 nm的位置处出现了强荧光峰, 这个峰是AuNPs费米能级的电子与sp或d带的空穴辐射复合产生的.     

Gold‐Aryl nanoparticles coated with polyelectrolytes for adsorption and protection of DNA against nuclease degradation

Binding DNA on nanoparticles was pursued to form nanoplatform for formation of non‐viral gene system. Carboxyl derivatized gold‐aryl nanoparticles can bind with biodegradable cationic polyelectrolytes such as polydiallyldimethylammonium chloride (PDADMAC). In our study, we used gold‐aryl nanoparticles (AuNPs) treated with PDADMAC to form conjugates with non‐thiol or non‐disulfide modified oligonucleotide DNA. Both AuNPs‐DNA and PDADMAC‐AuNPs‐DNA biomaterials were characterized using UV–Vis, dynamic light scattering (DLS), atomic force microscopy (AFM), transmission electron microscopy (TEM) and agarose gel electrophoresis. UV–Vis showed a red shift in the plasmon peak as compared with unconjugated AuNPs. DLS measurements also showed difference in the size of AuNPs‐DNA and PDADMAC‐AuNPs‐DNA. AFM and TEM results showed proper conjugation of DNA with AuNPs. Gel electrophoresis proved the presence of interaction between PDADMAC‐AuNPs and negatively charged DNA. The binding of DNA in the described bioconjugate enhanced its protection against nuclease degradation and prolonged its presence in the digestive environment of DNase‐I. From the results we expect that these biomaterials can be used in nanomedicine with emphasis on non‐viral gene system.     

Electrooxidation of ethylene glycol using gold nanoparticles electrodeposited on pencil graphite in alkaline medium

The electrooxidation of ethylene glycol(EG) on the surface of gold nanoparticles(AuNPs) in alkaline medium was investigated.AuNPs were electrodeposited on pencil graphite(PG) by fast scan cyclic voltammetry.Different sizes of AuNPs deposited on the surface of PG(AuNPs/PG) were used for the electrooxidation process.AuNPs were electrodeposited on PG at various deposition times in the same potential range but with different scan rates and scan cycles.Scanning electron microscopy(SEM),transmission electron microscopy(TEM) and X-ray diffraction(XRD) were used to visualize and characterize the prepared AuNPs/PG electrodes.Cyclic voltammograms were also used to investigate the electrooxidation of EG.The effects of EG and supporting electrolyte concentrations,scan rate,particle size of AuNPs and final potential limit on the electrooxidation process have been investigated.Further studies showed that the electrooxidation of EG is affected by temperature of the medium.The prepared AuNPs showed stability after long-term use.     

Vibrational spectroscopic characterization of 4-acylamidobenzenethiol-stabilized gold nanoparticles

A simple preparation method of gold nanoparticles (AuNPs) with 4-acylamidobenzenethiol derivative (BD) was improved to obtain the larger size of AuNPs which exhibited localized surface plasmon resonance. The spectroscopic characterizations of two kinds of BD-stabilized AuNPs were carried out by means of ATR-FTIR and Raman spectroscopy in order to clarify the conformation and orientation of BDs adsorbed on AuNPs. The relation between the stability of AuNPs and the adsorbed states of BDs were also discussed. The average sizes of the resulting AuNPs were 18 nm for BD1 and 30 nm for BD2, respectively. It was found that the BD1-capped AuNPs formed large aggregates. The results of vibrational spectroscopy revealed that loosely packed self-assembled monolayer (SAM) of BD1 molecules was formed on the surface of the AuNPs; on the other hand, densely packed SAM was formed in the case of BD2. We concluded the difference behavior between the two types of molecules was caused by the functional groups. The sulfuryl groups of BD2 induced highly ordered SAM and suppressed aggregate formation of AuNPs.     

Iron(III)‐Quantity‐Dependent Aggregation–Dispersion Conversion of Functionalized Gold Nanoparticles

Developing gold nanoparticles (AuNPs) with well‐designed functionality is highly desirable for boosting the performance and versatility of inorganic–organic hybrid materials. In an attempt to achieve ion recognition with specific signal expressions, we present here 4‐piperazinyl‐1,8‐naphthalimide‐functionalized AuNPs for the realization of quantitative recognition of Fe^III ions with dual (colorimetric and fluorescent) output. The research takes advantage of 1) quantity‐controlled chelation‐mode transformation of the piperazinyl moiety on the AuNPs towards Fe^III, thereby resulting in an aggregation–dispersion conversion of the AuNPs in solution, and 2) photoinduced electron transfer of a naphthaimide fluorophore on the AuNPs, thus leading to reversible absorption and emission changes. The functional AuNPs are also responsive to pH variations. This strategy for realizing the aggregation–dispersion conversion of AuNPs with returnable signal output might exhibit application potential for advanced nanoscale chemosensors.     

Colorimetric Enzyme Sensing Assays via In Situ Synthesis of Gold Nanoparticles

We report a successful facile and novel approach for in situ synthesis of gold nanoparticles (AuNPs) via enzymatic dephosphorylation reaction at room temperature. Fmoc-tyrosine phosphate and cytidine-5-mono phosphate are used to sense the activities of an enzyme alkaline phosphatase. Formation of AuNps is highly selective towards biomolecules and it is readily detected colorimetrically and UV–Vis analysis. In this procedure, dephosphorylated product plays both roles as reducing and stabilizing agent to direct the formation of AuNPs in aqueous media. Transmission electron microscopic study reveales that hexagonal AuNPs were synthesized by using Fmoc-tyrosine phosphate and alkaline phosphatase. Wide angle X-ray scattering data confirms the formation of AuNPs. FT-IR studies confirm that biomolecules play crucial role to stabilize the AuNPs by molecular interactions with the surface of AuNPs. In situ synthesized AuNPs are applied for the sensing of enzyme activity.     

Electropolymerized polythiophene photoelectrodes with density-controlled gold nanoparticles

A polythiophene thin film was fabricated on gold nanoparticle (AuNP)-deposited indium-tin-oxide (ITO) electrodes with electropolymerization, whereas AuNPs were predeposited on the ITO surface. A photocurrent via photoexcited polythiophene increased with AuNPs which was attributed to the localized surface plasmon resonance. Investigation of the AuNP-density dependence on the relative enhancement of photocurrent revealed the maximum effect at 14% of AuNP-density, while 68% of AuNP-density exhibited smaller photocurrent than the polythiophene electrode without AuNPs. We have revealed that the effects of AuNPs saturate in the fairly low density region, and that the excess AuNPs even in the range of submonolayer resulted in the decrement of photocurrents.     

Preparation of Resorcinarene-Functionalized Gold Nanoparticles and Their Catalytic Activities for Reduction of Aromatic Nitro Compounds

Resorcinarene‐functionalized gold nanoparticles (AuNPs) were prepared conveniently in aqueous solution in the presence of amphiphilic tetramethoxyresorcinarene tetraaminoamide. The obtained AuNPs were characterized and analyzed by UV‐vis, FT‐IR, XRD and TEM, respectively. The results showed that the size of AuNPs and the standard deviations were all decreasing with the increase of resorcinarene concentration. In addition, the catalytic activity of the obtained AuNPs in the reduction of aromatic nitro compounds was also investigated. In aqueous solution the reaction follows a first order kinetics and the size of AuNPs has influence on the rate of reduction.     

Hetero-assembly of gold nanoparticles on a DNA origami template

Hetero-assembling of spherical building blocks with well-defined spatial distribution holds great significance in developing chiral nanostructures. Herein, a strategy for hetero-assembling of gold nanoparticles(Au NPs) was demonstrated using rigid bifacial DNA origami as templates. By tuning the sizes and the fixed location of Au NPs on DNA origami, right-handed and left-handed Au NPs nanostructures were respectively constructed. Gel electrophoresis indicated the formation of the DNA origami-Au NPs complex and transmission electron microscopy(TEM) visually displayed the arrangement of Au NPs in these two chiral structures. The spatial configuration and 3D geometry of Au NPs were further illustrated by the stereographic TEM with tilting angles from ?30° to 30°. This strategy provides a universal approach to construct the asymmetrical 3D geometries, which may have potential applications in biomimicking and nanophotonics.     

溶胶-凝胶法原位复合PVA/HA水凝胶的结构表征与性能研究

采用溶胶-凝胶原位复合的方法制备了聚乙烯醇/羟基磷灰石生物活性复合水凝胶,探讨了HA含量对复合水凝胶结构性能的影响,用X射线衍射分析、红外光谱分析、DSC、扫描电镜等方法对HA在PVA水凝胶体系中的晶态结构及分散状态进行了表征,并与物理共混复合法进行了比较.研究发现,采用溶胶-凝胶法原位复合可在PVA水凝胶中形成具有生物活性的HA结晶结构,且分散良好,分布均匀.HA粉体作为异相成核剂,促进了PVA水凝胶基体的结晶,提高了复合水凝胶的力学性能.     

Gold nanoparticles prepared by glycinate ionic liquid assisted multi-photon photoreduction

We have successfully prepared gold nanoparticles (AuNPs) with flower-like and spherical morphology through multi-photon photoreduction (MPR) of an aqueous solution of HAuCl(4) and (2-hydroxyethyl) trimethylammonium glycinate ([HETMA][Gly]) ionic liquid (IL) through the use of a femtosecond laser. The results of (1)H NMR and UV-Vis absorption indicated that AuNPs were produced from the photoreduction of the [Gly]-Au(iii) complex. Spherical AuNPs of about 2.5 nm were obtained on the solution when irradiated for 2 h, then aggregated into flower-like AuNPs of several tens of nanometers assisted by the IL with an increase in the irradiation time. Furthermore, precipitates of spherical AuNPs with the size of around 15 nm were formed after being irradiated for 6 h. The mechanisms of the MPR reaction and controlled growth of AuNPs have also been discussed.     

Hybrid supramolecular hydrogels induced by Au nanoparticles protected with MPEG-b-PCL copolymers with α-cyclodextrin

To fabricate supramolecular hydrogel hybridised with well-dispersed gold nanoparticles (AuNPs), water-soluble AuNPs protected with methoxy poly(ethylene glycol)-b-poly(?-caprolactone) (MPEG-b-PCL) self-assembled monolayers (MPEG-b-PCL/AuNPs) were synthesised and used as guest molecules to interact with α-cyclodextrin (α-CD) in aqueous solutions. Transmission electron microscopy measurement results showed that the diameter of the AuNPs produced was about 6–10 nm with a narrow particle size distribution, and stained MPEG-b-PCL/AuNPs micelles made in water clearly displayed the formation of a core-shell structure with a single gold core per micelle. X-ray diffraction measurement results confirmed that there existed the characteristic peaks of both AuNPs and polypseudorotaxanes formed via the inclusion complexation of MPEG-b-PCL moieties with α-CD in as-obtained hydrogels. UV–visible spectra displayed that the same surface plasma resonance absorption peaks appeared at 526 nm for both aqueous dispersion of MPEG-b-PCL/AuNPs and resultant hybrid hydrogel with α-CD. Rheological measurements showed that the hybrid hydrogel has a lower mechanical strength and viscosity, and a relatively prolonged gelation time in comparison with the corresponding native hydrogel. The mechanical strength of the hydrogel nanocomposites could be tailored by modulating the concentration of MPEG-b-PCL/AuNPs and α-CD as well as the composition of MPEG-b-PCL/AuNPs.     

Structural organization of gold nanoparticles onto the ITO surface and its optical properties as a function of ensemble size

Self-assembly of citrate-stabilized gold nanoparticles (AuNPs) onto an optically transparent indium tin oxide (ITO) surface followed by neutralization of these particles using dodecanethiol as a surfactant have been demonstrated. X-ray photoelectron spectroscopic (XPS) studies revealed the partial removal of citrate ions from the immobilized AuNPs, which advances the dilution of electrostatic attraction between AuNPs and the APS (amino-terminated monolayer)-functionalized ITO surface. The resultant AuNPs restore their mobility to some extent and form small ensembles. Some of the immobilized AuNPs were completely removed from the surface due to neutralization, as confirmed by XPS studies. Interparticle distance and size of ensembles were manipulated by consecutive cycles of immobilization and neutralization of AuNPs. Controlled nanostructural fabrication progression, which leads to two-dimensional lateral growth of AuNPs, provides a method for systematically shifting the surface plasmon resonance band based on the increase in plasmon coupling among the closely placed AuNPs of an ensemble. The magnitude of shift increases with the size of ensemble. This manipulated chemical strategy offers a convenient and simple method to tune the optical properties of materials on a nanoscale.     

Effect of freeze-thawing on lipid bilayer-protected gold nanoparticles

In this study, varieties of lipid bilayer-protected gold nanoparticles (AuNPs) were synthesized through a simple wet chemical method, and then the effect of freeze-thawing on the as-prepared AuNPs was investigated. The freeze-thawing process induced fusion or fission of lipid bilayers tethered on the AuNPs. The UV-vis spectra and transmission electron microscopy experiments revealed that the disruption of lipid bilayer structures on the nanoparticles led to the fusion or aggregation of AuNPs. The role of freeze-thawing in the evolution of lipid bilayer-protected AuNPs was studied. The addition of adequate sucrose, a well-known cryoprotectant, effectively prevented the fusion or aggregation of lipid bilayer-protected AuNPs undergoing the freeze-thawing process. The possible mechanism of sucrose preserving the integrity of the lipid bilayer-protected AuNPs was also discussed.     

组装在贵金属基底上的金纳米粒子对CO的电化学催化氧化

研究了组装在Au, Pt电极表面的金纳米粒子对CO的电化学催化氧化行为, 首次在实验上观察到较大粒径金纳米粒子(粒径＞10 nm)对CO的电催化氧化活性. 考察了金粒子表面金氧化物对粒子电催化活性的影响, 发现表面金氧化物的形成是金纳米粒子对CO具有电催化氧化活性的前提. 对于相同粒径的金纳米粒子, 随着粒子表面金氧化物量的增加,催化活性增大.