Controlling the cellular uptake of gold nanorods

Gold nanorods coated with cetyltrimethylammonium bromide (CTAB), a cationic micellar surfactant used in nanorod synthesis, were rapidly and irreversibly internalized by KB cells via a nonspecific uptake mechanism. Internalized nanorods near the cell surface were monitored by two-photon luminescence (TPL) microscopy and observed to migrate toward the nucleus with a quadratic rate of diffusion. The internalized nanorods were not excreted but formed permanent aggregates within the cells, which remained healthy and grew to confluence over a 5-day period. Nonspecific nanorod uptake could be greatly reduced by displacing the CTAB surfactant layer with chemisorptive surfactants, particularly by the conjugation of poly(ethylene glycol) chains onto nanorods using in situ dithiocarbamate formation.     

Spectrally-resolved atomic-scale length variations of gold nanorods

Functionality of gold nanorod structures as ultra-sensitive optical rulers is demonstrated. Arrays of gold nanorods were fabricated by electron beam lithography and lift-off techniques with high accuracy and uniformity. Their longitudinal plasmon scattering spectra were found to exhibit extreme sensitivity to the length of the nanorods. This phenomenon enables optical detection of the nanorod length variations comparable to the thickness of a few atomic layers of gold.     

Crystal overgrowth on gold nanorods: tuning the shape, facet, aspect ratio, and composition of the nanorods

Electrochemically prepared Au nanorods were used as seeds for the overgrowth of thin shells of gold, silver, and palladium by using a mild reducing agent, ascorbic acid, in the presence of surfactants at ambient condition. The unique crystal facets of the starting nanorods results in anisotropic crystal overgrowth. The overgrowth rates along different crystallographical directions can be further regulated by adding foreign ions or by using different metal reduction methods. This overgrowth study provides insights on how different metal ions could be reduced preferentially on different Au nanorod surfaces, so that the composition, aspect ratio, shape, and facet of the resulting nanostructures can be rationally tuned. These surfactant-stabilized bimetallic Au(core)M(shell) (M=Au, Ag, Pd) nanorod colloids might serve as better substrates in surface-enhanced Raman spectroscopy as well as exhibiting enhanced catalytic properties.     

Changes in the shape and mobility of colloidal gold nanorods with electrospray and differential mobility analyzer methods

The potential of the electrospray technique in analyzing the structure of nonspherical colloidal particles that are below 100 nm in volume-equivalent diameter was demonstrated by online size measurement using a differential mobility analyzer (DMA) with a condensation nucleus counter (CNC) system. The measured mobility of gold nanorods was confirmed by electron microscope images and the theoretical calculation of particle mobility using the dynamic shape factor and slip correction factor. To evaluate the mobility, rod particles were modeled as both a cylinder and a prolate spheroid. This study also showed that the organic surfactant coated on rod particles might be removed and that the rod particles became spherical upon the elevation of the ambient temperature during the gas-phase dispersion of colloidal nanoparticles. Moreover, the thickness of the surfactants coated on rod particles was estimated by comparing the theoretically and experimentally obtained mobilities.     

pH-triggered assembly of gold nanorods

The self-assembly of surfactant-protected gold nanorods (aspect ratio 3.3 +/- 0.3, 20.6 +/- 5.5 nm width, and 67.5 +/- 9.0 nm length) into ordered structures using adipic acid is presented. As made, the gold nanorods are coated with cationic surfactant, which gives them a net positive charge in aqueous solution. The pH-dependent assembly is directed by electrostatic interactions between the positively charged nanorods and negatively charged, deprotonated adipic acid. Absorption spectra and light scattering measurements of these nanorods suggest that aggregation is initiated in solution in the presence of adipic acid at pH 7-8, but not at pH 3, to form small assemblies of nanorods. Zeta potential measurements show that the assembly is significantly less positively charged in the presence of deprotonated adipic acid than when adipic acid is fully protonated.     

Photochemical synthesis of gold nanorods

Gold nanorods have been synthesized by photochemically reducing gold ions within a micellar solution. The aspect ratio of the rods can be controlled with the addition of silver ions. This process reported here is highly promising for producing uniform nanorods, and more importantly it will be useful in resolving the growth mechanism of anisotropic metal nanoparticles due to its simplicity and the relatively slow growth rate of the nanorods.     

Organo-soluble chiral thiol-monolayer-protected gold nanorods

Here, we report the synthesis and characterization of organo-soluble chiral thiol-monolayer-protected gold nanorods. The resulting gold nanorods respectively covered with two opposite enantiomers via the strong covalent Au-S linkage were found to not only be stable in both organic media and solid state, but also show optical activity. Their circular dichroism (CD) spectra exhibited a mirror image relationship, indicating that enantiomeric thiol surfactant on gold surface can produce the corresponding enantiomeric gold nanorods. The densely packed azobenzene thiol monolayer on gold surface exhibited a photoresponsive behavior upon irradiation with 254 nm light instead of 365 nm light, which was found to have an effect on plasmonic absorption of gold nanorods.     

Fabrication and self-assembly of hydrophobic gold nanorods

Hydrophobic gold nanorods were fabricated from hydrophilic gold nanorods coated with hexadecyltrimethylammonium bromide by treating with mercaptopropyltrimethoxysilane (MPS) and subsequently octadecyltrimethoxysilane (ODS). The fabrication of the hydrophobic shell went through the process of (1) binding MPS onto the nanorods, (2) hydrolysis of methoxysilanes, and (3) immobilization of ODS by dehydration condensation. The 2- or 3-D ordered structures of hydrophobic nanorods were self-assembled by the evaporation of solvent on a substrate. The aspects of 2-D assemblies were dependent on the concentration of the nanorods, as was seen in transmission electron microscopic images. At a low concentration, the nanorods assembled parallel to the substrate, whereas they stood on the substrate at a high concentration. On the other hand, in a solid of the gold nanorods, the formation of the 3-D assembly was confirmed by small-angle X-ray scattering. The assembly consisted of hexagonal arrays of the gold nanorods and their lamellar accumulation.     

Directly monitoring the growth of gold nanoparticle seeds into gold nanorods

This paper describes the use of atomic force microscopy to directly image surface-attached 3-5 nm diameter gold nanoparticle seeds before and after seed-mediated growth into gold nanorods (Au NRs) and other shapes (spheres, triangles, and hexagons). Results show that Au NRs form from seeds growing in either one or two directions. A direct correlation exists between seed diameter and NR diameter; small diameter seeds form small diameter NRs. However, correlation between seed diameter and nanostructure shape or NR length is less evident. We describe our results in terms of growth mechanisms proposed in the literature and discuss possible reasons for the large size dispersity observed for surface-grown Au NRs. A better understanding of Au NR and other metal and semiconductor one-dimensional (1D) growth processes is necessary to improve synthesis, tailor their properties, and utilize 1D nanostructures for useful technological applications.     

High-temperature seedless synthesis of gold nanorods

We demonstrate seedless synthesis of gold nanorods at high temperatures up to 97 degrees C. Using the correct silver nitrate concentration is crucial for formation of rod-shaped particles at all temperatures. We observed a decrease of nanorod length with increasing temperature, while the width stays constant throughout the temperature range. From kinetics studies, we show 3 orders of magnitude increase in nanorod growth rate when the temperature is raised from room temperature to 97 degrees C. From the temperature dependence of the growth rate, we obtain a average activation energy for growth on all facets of 90 +/- 10 kJ mol(-1). High-temperature synthesis of gold nanorods presents a more attractive method for scalable flow-based production of gold nanorods.     

金纳米棒自组装的研究进展

金纳米棒具有独特的光电性能,其自组装形成的功能组装体能够展现出更加优异的整体协同性能,在纳米材料科学和生物医学领域中有广泛而重要的应用前景.本文从诱导自组装各种驱动作用力的角度,综述了金纳米棒自组装的最新研究进展,具体内容包括:表面张力引发的自组装、化学作用驱动如静电作用或氢键作用等引发的自组装以及生物分子识别作用引发的自组装.     

Preparation and optical properties of worm-like gold nanorods

A type of worm-like nanorods was successfully synthesized through conventional gold nanorods reacting with Na2S2O3 or Na2S. The generated worm-like gold nanorods comprise shrunk nanorod cores and enwrapped shells. Therefore, a gold-gold sulfide core-shell structure is formed in the process, distinguishing from their original counterparts. The formation of the gold chalcogenide layers was confirmed by transmission electron microscopy and X-ray photoelectron spectroscopy. Experimental results showed that the thickness of the gold chalcogenide layers is controllable. Since the increase of shell thickness and decrease of gold nanorod core take place simultaneously, it allows one to tune the plasmon resonance of nanorods. Proper adjustment of reaction time, temperature, additives and other experimental conditions will produce worm-like gold nanorods demonstrating desired longitudinal plasmon wavelength (LPW) with narrow size distributions, only limited by properties of starting original gold nanorods. The approach presented herein is capable of selectively changing LPW of the gold nanorods. Additionally, the formed worm-like nanorods possess higher sensitive property in localized surface plasmon resonance than the original nanorods. Their special properties were characterized by spectroscopic methods such as Vis-NIR, fluorescence and resonance light scattering. These features imply that the gold nanorods have potential applications in biomolecular recognition study and biosensor fabrications.     

Label-free biosensing with lipid-functionalized gold nanorods

The fabrication of a label-free mass spectrometry and optical detection-based biosensor platform for the detection of low-abundance lipophilic analytes in complex mixtures is described. The biosensor consists of a lipid layer partially tethered to the surface of a gold nanorod. The effectiveness of the biosensor is demonstrated for the label-free detection of a lipophilic drug in aqueous solution and a lipopeptide in serum.     

Multipole plasmon resonances in gold nanorods

The optical properties of gold rods electrochemically deposited in anodic aluminum oxide templates have been investigated. Homogeneous suspensions of rods with an average diameter of 85 nm and varying lengths of 96, 186, 321, 465, 495, 578, 641, 735, and 1175 nm were fabricated. The purity and dimensions of these rod nanostructures allowed us to observe higher-order multipole resonances for the first time in a colloidal suspension. The experimental optical spectra agree with discrete dipole approximation calculations that have been modeled from the dimensions of the gold nanorods.     

CeO2 nanorods and gold nanocrystals supported on CeO2 nanorods as catalyst

The formation mechanism of uniform CeO2 structure at the nanometer scale via a wet-chemical reaction is of great interest in fundamental study as well as a variety of applications. In this work, large-scale well-crystallized CeO2 nanorods with uniform diameters in the range of 20-30 nm and lengths up to tens of micrometers are first synthesized through a hydrothermal synthetic route in 5 M KOH solution at 180 degrees C for 45 h without any templates and surfactants. The nanorod formation involves dehydration of CeO2 nanoparticles and orientation growth along the 110 direction in KOH solution. Subsequently, gold nanoparticles with crystallite sizes between 10 and 20 nm are loaded on the surface of CeO2 nanorods using HAuCl4 solution as the gold source and NaBH4 solution as a reducing agent. The synthesized Au/CeO2 nanorods demonstrate a higher catalytic activity in CO oxidation than the pure CeO2 nanorods.     

Hemoprotein bioconjugates of gold and silver nanoparticles and gold nanorods: structure-function correlations

Bioconjugates of the hemoproteins, myoglobin, and hemoglobin have been synthesized by their adsorption on spherical gold and silver nanoparticles and gold nanorods. The adsorption of hemoproteins on the nanoparticle surface was confirmed by their molecular ion signatures in matrix assisted laser desorption ionization mass spectrometry and specific Raman features of the prosthetic heme b units. High-resolution transmission electron microscopy (HRTEM) and UV-visible spectroscopy showed that the particles retain their morphology and show aggregation only in the case of silver. The binding of azide ion to the Fe(III) center of the prosthetic heme b moiety caused a red shift of the Soret band, both in the case of the bioconjugates and in free hemoproteins. This was further confirmed by the characteristic signature at 2050 cm-1 in the Fourier-transform infrared spectra, which corresponds to the asymmetric stretching of the Fe(III) bound azide. The retention of the chemical behavior of the prosthetic heme group after adsorption on the nanoparticle is interesting due to its implications in nanoparticle supported enzyme catalysis. The absence of morphology changes after the reaction of bioconjugates with azide ion observed in HRTEM studies implies the stability of nanoparticles under the reaction conditions. All these studies indicate the retention of protein structure after adsorption on the nanoparticle surface.     

Cysteine-assisted growth of silver on gold nanorods

Au–Ag core–shell (Au@Ag) nanobars could be synthesized from gold nanorod (NR) seeds with cysteine additives by a two-step process of reaction temperatures. The lateral sides of gold NRs surrounded by surfactant bilayers render cysteine additives binding on both ends of the NRs, and restricted silver deposition to their lateral sides at room temperature. Further, silver deposition can take place at first on the pre-formed silver layers on the lateral sides at higher temperatures and finally resulted in the formation of Au@Ag nanobars in which gold NRs are in the corner positions of the nanobars and their longitudinal axes parallel to the longer sides of the nanobars.     

Plasmon mode imaging of single gold nanorods

We have investigated two-photon-induced photoluminescence images and spectra of single gold nanorods by using an apertured scanning near-field optical microscope. The observed PL spectrum of single gold nanorod can be explained by the radiative recombination of the electron-hole pair near the X and L symmetry points. PL images reveal characteristic features reflecting an eigenfunction of a specific plasmon mode as well as electric field distributions around the nanorod.