Matryoshka-caged gold nanorods: Synthesis,plasmonic properties,and catalytic activity

Matryoshka-caged gold nanorods (mCGNRs) were successfully synthesized by alternating between a seed-mediated silver-coating method and galvanic replacement reactions (GRRs). As the number of matryoshka layers of the mCGNRs increased, the plasmon resonance peak broadened and was red-shifted, and the catalytic activity towards the reduction of 4-nitrophenol (4-NTP) increased. When mCGNRs with 6 layers were used as nanocatalysts in the reduction of 4-nitrophenol, the reaction rate coefficient was 5.2- and 3.7-times higher than that of the gold-nanorod- and caged-gold-nanorod-catalyzed reductions of 4-nitrophenol, respectively. In addition, the surface-plasmon-resonance-based absorption of light enhanced the catalytic performance of the mCGNRs. With the support of a polyurethane foam, the mCGNRs synthesized in this study can be applied as recyclable heterogeneous catalysts for the reduction of 4-nitrophenol.

Open image in new window

     

Chemical functionalisation and arrangement of ultrasmall gold clusters in Langmuir-Blodgett films

Phosphine ligand-stabilised gold clusters with core diameters in the region of 1–3 nm were embedded in a polymer Langmuir film matrix and deposited onto substrates suitable for TEM investigation. The Langmuir layers were either transferred from pure water or a subphase containing a thiol ligand. There is evidence for ligand exchange without the decomposition of the cluster material. TEM images reveal different lateral cluster arrangements in dependence of the subphase composition and the presence of head group charges in the polymer matrix. In addition, the size distribution of the clusters is affected by thiol addition to the subphase leading to smaller particles with a decreased size variation.     

Synthesis,stability, and in vitro oral cancer cell toxicity of human serum albumin stabilised gold nanoflowers

Gold nanoflowers (GNFs) prepared by reduction of HAuCl₄ by ascorbic acid were capped with human serum albumin (HSA) by either electrostatic or covalent attachment to prevent their self‐aggregation. Measurement of surface plasmon resonance absorbance changes under different stress conditions showed that GNFs stabilised by covalent attachment of HSA were more stable than those stabilised by electrostatic attachment. Cytotoxicity of the covalently conjugated GNF was also studied in cultured human oral cancer cell lines by measuring the metabolic activity via 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay.Inspec keywords: proteins, molecular biophysics, biomedical materials, reduction (chemical), gold, cellular biophysics, nanofabrication, biochemistry, surface plasmon resonance, cancer, nanomedicine, materials preparation, nanostructured materialsOther keywords: Au, human serum albumin stabilised gold nanoflowers, cytotoxicity, in vitro oral cancer cell toxicity, stress conditions, surface plasmon resonance absorbance, 3‐(4,5‐dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide assay, self‐aggregation, covalent attachment, electrostatic attachment, ascorbic acid, cultured human oral cancer cell lines     

Human serum albumin mediated self-assembly of gold nanoparticles into hollow spheres

The assembly of nanoparticles in topologically predefined superstructures is an important area in nanoscale architecture. In this paper, we report an unusual aggregation phenomenon involving L-lysine capped gold nanoparticles and human serum albumin into hollow nanospheres. The electrostatic interaction between positively charged L-lysine capped gold nanoparticles and negatively charged human serum albumin at physiological pH led to the assembly of the gold nanoparticles into hollow spheres. The phenomenon can be explained by the dry hole opening mechanism.     

Three-dimensional morphology and crystallography of gold nanorods

We determine the three-dimensional shape, to within 1 nm resolution, of single-crystal gold nanorods grown in the presence of silver ions using electron tomography and thickness profile measurements. We find that, contrary to the current literature, the octagonal side-facets are sparsely packed atomic planes all belonging to the same symmetry-equivalent family, {0 5 12}. Furthermore, the rod ends terminate in a pyramid with slightly different facets, and each pyramid is connected to the sides by four small {0 5 12} "bridging" facets.     

Self-assembly of small gold colloids with functionalized gold nanorods

We present a general strategy to stabilize gold nanorod suspensions with mono- and bifunctional polyethylene glycol (PEG) and to attach a controlled number of nanoparticles or biomolecules. Characterization by gel electrophoresis, transmission electron microscopy (TEM), and optical dark-field microscopy show the specific binding of functionalized nanorods to their target while avoiding nonspecific binding to substrates, matrices, and other particles. Such nanorods are well suited for self-assembly of nanostructures and single-molecule labeling.     

Surface-driven bulk reorganization of gold nanorods

Molecular dynamic simulations are used to study the structural stability of gold nanorods upon heating. We show that the global stability of the rod is governed by the free energetics of its surface. In particular, an instability of surface facets nucleates a bulk instability that leads to both surface and bulk reorganization of the rod. The surface reorganizes to form new, more stable, {111} facets, while the underlying fcc lattice completely reorients to align with this new surface structure. Rods with predominantly {111} facets remain stable until melting.     

Gelation effect on the synthesis of high-aspect-ratio gold nanorods

The growth process of high-aspect-ratio gold nanorods in gelled surfactant solution was studied. As for the application of gold nanorods, the surface plasmon is quite useful, whose absorption depends on their aspect ratio. Hence it is important to synthesize gold nanorods with favorable aspect ratio in high yield. For shorter nanorods (aspect ratio < -10), the synthesis and the growth mechanism have been studied well. For the longer nanorods (aspect ratio > -30), however, the growth mechanism has not yet been understood well, although it has been known that the high-aspect-ratio gold nanorods could be synthesized in high yield in gelled surfactant solution. In this paper, we studied the relationship between the growth process of high-aspect-ratio gold nanorods and the gelation of surfactant growth-solution. Small angle X-ray scattering (SAXS) revealed the microscopic feature of gelation as the structural transition of self-assembly of surfactant molecules from micellar to lamellar. These results will be helpful for better understanding on the growth mechanism of high-aspect-ratio gold nanorods.     

The effect of gold nanorods on cell-mediated collagen remodeling

Cardiac fibroblasts, the noncontractile cells of the heart, contribute to myocardial maintenance through the deposition, degradation, and organization of collagen. Adding polyelectrolyte-coated gold nanorods to three-dimensional constructs composed of collagen and cardiac fibroblasts reduced contraction and altered the expression of mRNAs encoding beta-actin, alpha-smooth muscle actin, and collagen type I. These data show that nanomaterials can modulate cell-mediated matrix remodeling and suggest that the targeted delivery of nanomaterials can be applied for antifibrotic therapies.     

Multiple surface plasmon modes for a colloidal solution of nanoporous gold nanorods and their comparison to smooth gold nanorods

The paper represents a novel approach to investigating localized surface plasmon (LSP) resonance modes of nanoporous Au nanorods (NRs) in a solution phase with control over surface morphology. Au NRs, which have distinctive features such as nanopores and ligaments, showed interesting LSP resonance modes depending on the surface morphology and the total length of the structure. Compared with the analogous smooth surface NRs, the LSP modes of nanoporous NRs are red-shifted, which can be interpreted as a longer effective rod length and larger amplitude of plasmon oscillation.     

人血清蛋白与重金属离子相互作用的荧光光谱

通过荧光光谱技术研究重金属离子与人血清蛋白(HSA)间的结合作用机制.测量了人血清蛋白与重金属离子Pb2+,Cr6+,Cu2+在290K和300K温度下相互作用的荧光光谱,建立猝灭方程.3种重金属离子与HSA的猝灭均属于静态猝灭,根据静态猝灭方程Stern-Volmer分别计算出290K和300K温度下HSA与3种重金属离子相互作用结合常数,290K下结合常数Ksv分别为1.731×103,5.580×103,4.461×104;300K下结合常数Ksv分别为1.354×103,5.418×103,4.461×104,结合位点数分别为1.237,1.528,0.506.证明了重金属离子Pb2+,Cr6+,Cu2+与HSA之间的相互作用是自发的.     

硅掺杂羟基磷灰石生物活性微粉对人血清白蛋白的吸附特性

对含硅羟基磷灰石(Si-HA)与人血清白蛋白(HSA)的吸附特性及动力学特征进行了研究,计算了表观活化能,用等温吸附曲线进行拟合。结果表明,该吸附属于Langmuir型。Si-HA和HA吸附HSA的表观活化能分别为21.28和35.57 kJ.mol-1,20℃下吸附反应的速率常数分别为1.48和1.34 min-1,饱和吸附量分别为25.34和21.34 mg.g-1,Si-HA具有比纯HA更好的吸附优势。通过XRD、FTIR及荧光光谱分析,探讨了HSA在Si-HA和HA表面的吸附作用机制,表明Si-HA与蛋白表面吸附反应是以化学吸附为主、包含物理吸附的混合吸附过程。从分子结构的角度揭示了Si-HA和HA吸附蛋白质性能的差异,为进一步探讨Si-HA和HA生物相容性提供了新途径。     

Synthesis of gold nanorods in organic media

A seed mediated approach for the synthesis of anisotropic rod shaped gold nanoparticles in organic media (toluene) is demonstrated. Pre-formed gold nanoparticles stabilized in toluene by 4-hexadecylaniline (HDA) are used as seeds. These when reacted with 1-octadecylamine (ODA) hydrophobised chloroaurate ions in toluene lead to the formation of gold nanorods. ODA or alkylamines of different chain lengths which are the chloroaurate ion phase transfer agent have been found to play a key role in the formation of the nanorods. The gold nanorods that have a five-fold symmetry evolve from multiply twinned particles and are bound at the tips by [1 11] faces and at the sides by [100] faces. The gold nanorods have been shown to grow under the shape directing effect of the alkylamines which stabilize the high energy [100] faces. The concentration of the alkylamines has been found to play a critical role in the formation of the gold nanorods. Higher concentrations of the alkylamines lead to formation of spherical particles, at times of narrow size distribution.     

Quantitative optical trapping of single gold nanorods

We report a quantitative analysis of the forces acting on optically trapped single gold nanorods. Individual nanorods with diameters between 8 and 44 nm and aspect ratios between 1.7 and 5.6 were stably trapped in three dimensions using a laser wavelength exceeding their plasmon resonance wavelengths. The interaction between the electromagnetic field of an optical trap and a single gold nanorod correlated with particle polarizability, which is a function of both particle volume and aspect ratio.     

Luminescence quantum yield of single gold nanorods

We study the luminescence quantum yield (QY) of single gold nanorods with different aspect ratios and volumes. Compared to gold nanospheres, we observe an increase of QY by about an order of magnitude for particles with a plasmon resonance >650 nm. The observed trend in QY is further confirmed by controlled reshaping of a single gold nanorod to a spherelike shape. Moreover, we identify two spectral components, one around 500 nm originating from a combination of interband transitions and the transverse plasmon and one coinciding with the longitudinal plasmon band. These components are analyzed by correlating scattering and luminescence spectra of single nanorods and performing polarization sensitive measurements. Our study contributes to the understanding of luminescence from gold nanorods. The enhanced QY we report can benefit applications in biological and soft matter studies.     

Grafting of gold nanoparticles and nanorods on plasma-treated polymers by thiols

Grafting of gold nanoparticles and nanorods on the surface of polymers, modified by plasma discharge, is studied with the aim to create structures with potential applications in electronics or tissue engineering. Surfaces of polyethyleneterephthalate and polytetrafluoroethylene were modified by plasma discharge and subsequently, grafted with 2-mercaptoethanol, 4,4′-biphenyldithiol, and cysteamine. The thiols are expected to be fixed via one of –OH, –SH or –NH₂ groups to reactive places on the polymer surface created by the plasma treatment. “Free” –SH groups are allowed to interact (graft) with gold nanoparticles and nanorods. Gold nano-objects were characterized before grafting by transmission electron microscopy and UV–Vis spectroscopy. X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and electrokinetic analysis (zeta potential determination) were used for the characterization of polymer surface at different modification phases. It was proved by FTIR and XPS measurements that the thiols were chemically bonded on the surface of the plasma-treated polymers, and they mediate subsequent grafting of the gold nano-objects. On the surfaces, modified polymers were indicated some objects by AFM, size of which was dramatically larger in comparison with that of original nanoparticles and nanorods. This result and the other results of UV–Vis spectroscopy indicate an aggregation of deposited gold nano-objects.     

Photoacoustic flow measurements based on wash-in analysis of gold nanorods

In this study, photoacoustic flow measurement methods based on wash-in analysis are presented. These methods use the rod-to-sphere shape transformations of gold nanorods induced by pulsed-laser irradiation. Due to the shape dependence of the optical absorption of the gold nanorods, these shape transitions are associated with a change in the peak optical absorption wavelength. Pulsed-laser irradiation at the wavelength corresponding to the peak optical absorption of the original gold nanorods allows the particles that undergo shape changes to be viewed as "being destructed" by the laser irradiation at that wavelength, hence, flow information can be derived from the change in ultrasound intensity that is directly related to the wash-in rate of the gold nanorods and the laser intensity. Two flow estimation methods based on the wash-in analysis are described. The first method first applies high-energy laser pulses that induce shape changes in all the nanorods. A series of low-energy pulses then are applied to monitor the acoustic signal change as new nanorods flow into the region of interest. The second method uses single-energy laser pulses such that the "destruction" and "detection" are performed simultaneously. The simulation results show that it is valid to fit the time-intensity curves by exponential models. To demonstrate the validity of the proposed methods, an Nd:YAG pulsed laser operating at 1064 nm was used for optical irradiation, and a 1-MHz ultrasonic transducer was used for acoustic detection. Gold nanorods with a peak optical absorption at 1018 nm and a concentration of 0.26 nM were used to estimate flow velocities ranging from 0.35 to 2.83 mm/s. The linear regression results show that the correlation coefficients between the measured velocities and the true values are close to unity (> or = 0.94), thus demonstrating the feasibility of the proposed photoacoustic techniques for relative flow estimation.     

In situ organization of gold nanorods on mixed self-assembled-monolayer substrates

A method is described for assembling gold nanorods, end-to-end, into long chains attached on top of a mixed self-assembled monolayer that has been functionalized with streptavidin. Methods to prepare chains of nanorods in colloidal suspension have been reported by others, but our protocol offers a way to directly form such structures on a substrate. The rods are spaced approximately 5 nm apart in the resulting chains, which extend for over a micrometer in length. The assembly and morphology of the nanorod structures were characterized by surface plasmon resonance spectroscopy, as well as by scanning electron microscopy and scanning probe microscopy. Structures of this type could conceivably serve as plasmonic waveguides in future nanodevices.