Design of Gold Nanoparticles for Magnetic Resonance Imaging

Improving the sensitivity of magnetic resonance imaging (MRI), a powerful non‐invasive medical imaging technique, requires the development of novel contrast agents with a higher efficiency than gadolinium chelates such as DTPA:Gd (DTPA: diethylenetriaminepentaacetic acid) that are currently used for clinical diagnosis. To achieve this objective, the strategy that we have explored involves the use of gold nanoparticles as carriers for gadolinium chelates. These nanoparticles are obtained by reducing a gold salt in the presence of a dithiolated derivative of DTPA. Characterization of these particles by transmission electron microscopy (TEM), X‐ray diffraction (XRD), thermogravimetric analysis (TGA), colorimetric titration, and X‐ray photoelectron spectroscopy (XPS) reveals the presence of a multilayered shell containing about 150 ligands on 2–2.5 nm sized particles. These particles exhibit a high relaxivity (r₁ = 585 mM ^–1 s^–1 as compared to 3.0 mM ^–1 s^–1 for DTPA:Gd), rendering them very attractive as contrast agents for MRI.     

Oligothia Dendrimers for the Formation of Gold Nanoparticles

The synthesis and characterization of oligothia dendrimers and their use for the formation of gold nanoparticles is described. The role played by these dendrimers in controlling the stability and size of the particles is discussed. It is shown that the generation of the dendrimers, as well as the position of the sulfur atoms in the dendritic structure (S₆G1 and S₉G1), influence the formation and reactivity of the nanoparticles. UV‐visible spectroscopy, ¹H nuclear magnetic resonance spectroscopy and high‐resolution transmission electron microscopy have been employed for the characterization of the nanoparticles. Furthermore, purification by Soxhlet extraction has been performed.     

纳米金增敏的压电乙肝IgM免疫传感器研究

研究了在石英晶体表面上组装纳米金,利用水溶性聚合物聚乙二醇(PEG)为凝集剂,加入聚乙烯醇(PVA)增加其凝聚力,利用金纳米粒子对传感器的信号放大增敏作用、比表面积大和较好的生物相溶性等优良特征,在晶振表面固定乙肝核心抗体(IgM),构建了一种高灵敏度的乙肝液相压电免疫传感器。应用于样本检测。该方法与酶联免疫分析方法(ELISA)无显著差异。     

Thermosensitive Nanostructures Comprising Gold Nanoparticles Grafted with Block Copolymers

Binary thermosensitive nanocomposites are fabricated by grafting block copolymers of poly(N‐isopropylacrylamide) and poly(methoxy‐oligo(ethylene glycol) methacrylate) onto gold nanoparticles through consecutive, surface‐initiated, atom‐transfer radical polymerization (ATRP). These Au@copolymer nanocomposites display a well‐defined core/shell nanostructure and have two thermosensitive points near 33 and 55 °C in an aqueous suspension corresponding to the thermally induced conformational transition of inner homopolymer segments and outer oligo(ethylene glycol)‐containing copolymer layer, respectively. Silver nanoparticles trapped within Au@copolymer nanocomposites with weakly crosslinked shells display thermally modulated catalytic activity as heterogeneous catalysts because of the thermosensitive collapse of the polymer layers.     

Electrooptical Properties of TiO2 Doped with Gold Nanoparticles

Semiconductors - In this work, a versatile method to increase the optical response of oxide nanostructures is described. Thin TiO2 films with buried gold nanoparticles (TiO2-AuNP) were synthesized...     

Fluorescence of Colloidal Gold Nanoparticles is Controlled by the Surface Adsorbate

Fluorescent gold nanoparticles are important biological labels, in particular for combined optical and electron microscopy. It is reported that density and type of surface ligands have key influence on the dominant UV‐vis fluorescence band in positively and negatively charged gold nanoparticles capped with citrate, gold oxide, and cetyltrimethyl ammonium bromide (CTAB). The peak excitation and emission energies and fluorescence intensities vary with nanoparticle size, reflecting changes in surface charge and surface potential as well as a varying density of surface adsorbates. The fluorescence peak shifts, the evolution of zeta potentials, and fluorescence intensity trends are explained by a model of the principal fluorescence transitions that takes into account the nanoparticle surface conditions, such as the adhesion of ligands. Varying surface ligands is a simple strategy to optimize fluorescence intensity and to design spectral properties of gold nanoparticles.     

金纳米粒子作掩模的硅纳米柱阵列的加工

利用自组装的方法在硅基片表面形成一层均匀的金纳米粒子掩模,分析了偶联剂对自组装的影响,以金纳米粒子作掩模进行反应离子刻蚀,研究了刻蚀时间对硅纳米柱阵列的影响,提供了一种简单、便宜并且有效的在硅基底上大面积形成纳米柱阵列的纳米加工方法。实验中发现,超过一定刻蚀时间时,有过刻蚀现象发生,在120 s刻蚀时间下,得到了直径小于20 nm,深宽比高达10∶1以上规则、致密、大面积分布的硅纳米柱或硅纳米锥状结构。     

Preparation and Organization of Nanoscale Polyelectrolyte‐Coated Gold Nanoparticles

The layer‐by‐layer (LbL) desposition of oppositely charged polyelectrolytes from adsorption solutions of different ionic strength onto ～7 nm diameter carboxylic acid‐derivatized gold nanoparticles has been studied. The polyelectrolyte‐modified nanoparticles were characterized by UV‐vis spectrophotometry, microelectrophoresis, analytical ultracentrifugation, and transmission electron microscopy. UV‐vis data showed that the peak plasmon absorption wavelength of the gold nanoparticles red‐shifted after each adsorption step, and microelectrophoresis experiments revealed a reversal in the surface charge of the nanoparticles following deposition of each layer. These data are consistent with the formation of polyelectrolyte layers on the nanoparticles. Analytical ultracentrifugation showed an increase in mean nanoparticle diameter on adsorption of the polyelectrolytes, confirming the formation of gold‐core/polyelectrolyte‐shell nanoparticles. Transmission electron microscopy studies showed no signs of aggregation of the polyelectrolyte‐coated nanoparticles. The adsorption of the polyelectrolyte‐coated gold nanoparticles onto oppositely charged planar supports has also been examined. UV‐vis spectrophotometry and atomic force microscopy showed increased amounts of nanoparticles were adsorbed with increasing ionic strength of the nanoparticle dispersions. This allows control of the nanoparticle surface loading by varying the salt content in the nanoparticle dispersions used for adsorption. The LbL strategy used in this work is expected to be applicable to other nanoparticles (e.g., semiconductors, phosphors), thus providing a facile means for their controlled surface modification through polyelectrolyte nanolayering. Such nanoparticles are envisaged to have applications in the biomedical and bioanalytical fields, and to be useful building blocks for the creation of advanced nanoparticle‐based films.     

Ultra-Small ATP-Decorated Gold Nanoparticles for Targeting Amyloid Fibrils in Neurodegenerative Diseases

Ultrafine Gold nanoparticles (Au NPs) functionalized with various biomolecules constitute an alternative to antibodies as anti-amyloidogenic agents. However, generating stable ultrafine Au NPs with high surface activity is challenging. Here, the capacity of phosphate groups in biomolecules is used to stabilize Au NPs. The characteristics of Au NPs decorated with adenosine mono-, di-, and tri-phosphate are compared as well as adenosine and peptide nucleic acid-containing adenosine as controls. Among them, ATP-Au NPs are found to be superior having small size (2–4 nm) and stability (for several months) when analysed by spectroscopy and electron microscopy. Spectroscopy analysis also revealed that each ATP-stabilized Au NP is decorated with 7–8 molecules of ATP. ThT binding analysis and TEM imaging showed that the ATP-Au NPs efficiently prevented amyloid fibril formation in vitro by Aβ-42, α-Synuclein as well as by the Glucosylceramide metabolite, and disaggregated their pre-formed fibrils. NMR analysis revealed the interaction of the ATP-Au NPs with the amyloid fibrils. The ATP-Au NPs are safe toward cultured SH-SY5Y cells and when co-incubated with α-Synuclein amyloids inhibited their cytotoxicity and readily enter the cells to inhibit formation of amyloid fibrils within them. The results indicates the pharmacological potentials of ATP decorated Au NPs.     

Optical Properties of Quasi One‐Dimensional Chains of Gold Nanoparticles

Nanopores in alumina membranes can serve as reaction vessels for the generation of nanosized gold particles. In addition, they enable a quasi one‐dimensional arrangement of nanoparticles, the optical properties of which can easily be investigated due to their transparency in the visible and near ultraviolet (UV) regions. Gold colloids inside the pores were produced either by thermal decomposition of [Au₅₅(PPh₃)₁₂Cl₆] clusters or by loading the pores with preformed colloids. The clusters as well as the colloids were transferred into the pores by simple immersion, and if necessary supported by applying a vacuum. The [Au₅₅(PPh₃)₁₂Cl₆] clusters were decomposed over the temperature range of 100 to 800 °C, using pores of different diameters. Transmission electron microscopy (TEM) was used to investigate the resulting nanoparticles. At decomposition temperatures up to ca. 500 °C, no specific influence of pore size or temperature was observed: 4–5 nm colloids were formed. However, temperatures > 500 °C resulted in colloids of up to 10–11 nm being formed. The optical properties of these and of preformed gold colloids in the membranes were studied. The extinction spectra of the colloidal assemblies generated from clusters exhibited two absorption peaks, caused by excitation of the plasmon resonance along the long and the short axes of the wire‐like arranged particles. The optical extinctions were measured with unpolarized and polarized light (0 and 90°). Depending on the angle of polarization, the polarized light caused either a blue‐ or a red‐shift in the absorption maximum. Theoretical calculations, using the so‐called generalized Mie theory and Maxwell Garnet theory, confirmed the experimentally observed behavior of these gold/alumina nanocomposites.     

原位形成的金纳米颗粒对溶菌酶结构的影响

在溶菌酶水溶液中,用NaBH4原位还原HAuCl4得到了溶菌酶稳定的金纳米颗粒。这些溶菌酶稳定的金纳米颗粒具有亲水性、生物兼容性以及良好的溶胶稳定性。紫外-可见光谱、透射电子显微镜以及动态光散射实验对所得产物的表征结果说明实验中形成了分散性良好的直径约2 nm的金纳米颗粒。傅里叶变换红外光谱和圆二色谱实验表明,与金纳米颗粒作用之后的溶菌酶分子仍然保持了结构的完整性,金纳米颗粒的形成没有对蛋白质的一级和二级结构造成影响。基于其良好的溶胶稳定性及生物兼容性,这些溶菌酶稳定的金纳米颗粒在纳米科技和生物医学领域具有潜在的应用价值。     

基于金纳米颗粒的激光钛合金表面处理研究

钛合金的表面质量直接决定了种植体的成活率。针对传统表面处理方法带来的问题,文中基于时域有限差分法,提出了一种基于直径200 nm金颗粒的钛合金表面激光处理方法,研究了激光参数对钛合金表面光场分布的影响规律。仿真结果表明,由200 nm金纳米颗粒激发的近场增强分布区域为环形;增强倍数超过了6 500倍;通过改变入射光的角度可以进一步提高增强倍数;而背景折射率对金纳米颗粒激发的近场增强效果影响微小,能够在多种介质中进行表面处理。     

Tuning Dichroic Plasmon Resonance Modes of Gold Nanoparticles in Optical Thin Films

A simple method is presented to tune the gold surface plasmon resonance (SPR) modes by growing anisotropic nanoparticles into transparent SiO₂ thin films prepared by glancing angle deposition. In this type of composite film, the anisotropy of the gold nanoparticles, proved by gracing incidence small angle X‐ray scattering, is determined by the tilted nanocolumnar structure of the SiO₂ host and yields a strong film dichroism evidenced by a change from an intense colored to a nearly transparent aspect depending on light polarization and/or sample orientation. The formation in these films of lithographic non‐dichroic SPR patterns by nanosecond laser writing demonstrates the potentialities of this procedure to develop novel optical encryption or anti‐counterfeiting structures either at micrometer‐ or macroscales.     

Colloidal Photonic Crystals Doped with Gold Nanoparticles: Spectroscopy and Optical Switching Properties

Polystyrene artificial opals with few gold nanoparticles (AuNp) embedded in the interstices (doping) are grown by using the meniscus technique starting from a mixed suspension of microspheres and AuNp. Samples having different sphere diameters and nanoparticle loads have been prepared. Their reflectance spectra clearly show a dramatic bathochromic shift of the photonic stop band (up to 1400 cm^–1) and a reduction of its full width half maximum, due to an increase of the effective refractive index of about 8 % with respect to bare opals, which is accounted for by analytical theoretical models. Reflectance spectra do not show any direct evidence of AuNp absorption even at the higher AuNp doping level. Nanosecond transient absorption measurements on these systems indicate that a variation of transmission (optical switching) of about 150 % is observed for AuNp doped opals upon photoexcitation with 9 ns laser pulses at 532 nm. No switching is instead observed for bare opals.     

Strong Photoacoustic Signal Enhancement by Coating Gold Nanoparticles with Melanin for Biomedical Imaging

Photoacoustics is a powerful biomedical imaging and detection technique, because it is a noninvasive, nonionizing, and low‐cost method facilitating deep tissue penetration. However, suitable contrast agents need to be developed to increase the contrast for in vivo imaging. Gold nanoparticles are often discussed as potential sonophores due to their large absorption cross‐section and their tunable plasmon resonance. However, disadvantages such as toxicity and low photoacoustic efficiency in the tissue transparency window prevail, preventing their clinical application. As a result, there remains a strong need to develop colloidal photoacoustic contrast agents which absorb in the tissue transparency window, exhibit high photoacoustic signal, and are biocompatible. Here, a facile synthetic approach is presented to produce melanin shells around various gold nanoparticle geometries, from spheres to stars and rods. These hybrid particles show excellent dispersability, better biocompatibility, and augmented photoacoustic responses over the pure melanin or pristine gold particles, with a rod‐shape geometry leading to the highest performance. These experimental results are corroborated using numerical calculations and explain the improved photoacoustic performance with a thermal confinement effect. The applicability of melanin coated gold nanorods as gastrointestinal imaging probes in mouse intestine is showcased.     

Supported Faceted Gold Nanoparticles with Tunable Surface Plasmon Resonance for NIR‐SERS

A novel dry plasma methodology for fabricating directly stabilized substrate‐supported gold nanoparticle (NP) ensembles for near infrared surface enhanced Raman scattering (NIR SERS) is presented. This maskless stepwise growth exploits Au‐sulfide seeds by plasma sulfidization of gold nuclei to produce highly faceted Au NPs with a multiple plasmon resonance that can be tuned from the visible to the near infrared, down to 1400 nm. The role of Au sulfidization in modifying the dynamics of Au NPs and of the corresponding plasmon resonance is discussed. The tunability of the plasmon resonance in a broad range is shown and the effectiveness as substrates for NIR SERS is demonstrated. The SERS response is investigated by using different laser sources operating both in the visible and in the NIR. SERS mapping of the SERS enhancement factor is carried out in order to evaluate their effectiveness, stability, and reproducibility as NIR SERS substrates, also in comparison with gold NPs fabricated by conventional sputtering and with the state‐of‐the‐art in the current literature.     

Reversible and Rapid Laser Actuation of Liquid Crystalline Elastomer Micropillars with Inclusion of Gold Nanoparticles

It is highly desirable for liquid crystal elastomer (LCE) based microactuators to activate and actuate in a highly controlled fashion without perturbing the surrounding environment. To reach this goal, in this study, a novel experimental protocol is developed to successfully incorporate gold nanosphere (AuNS) and gold nanorod (AuNR) into polyacrylate based LCE elastomer to fabricate LCE/AuNR and LCE/AuNS micropillars or microactuators. The effect of gold nanoparticle inclusion has been studied by spectroscopy (UV–vis‐near‐infrared), microscopy (transmission electron microscopy), thermal analysis (differential scanning calorimetry and thermogravimetric analysis), and x‐ray scattering (wide‐angle x‐ray scattering and small‐angle x‐ray scattering). Finite element analysis is performed to examine the feasibility of utilizing the photothermal effect of AuNR/AuNS to enable photothermal actuation of LCE/AuNR and LCE/AuNS micropillars. The comparative experimental studies on the thermal and photothermal actuation behavior of the LCE, LCE/AuNS, and LCE/AuNR micropillar suggested that AuNR is an excellent candidate for developing high‐performance LCE actuators with photothermal actuation capability. With inclusion of less than 1 wt% of AuNR, the very high maximum actuation strain (30%) and rapid response (a few seconds) have been achieved in LCE/AuNR micropillar actuators under 635 nm laser irradiation.