Danielle K. Smith

Iodide in CTAB prevents gold nanorod formation.

The gold nanocrystal seed-mediated approach using cetyltrimethylammonium bromide (CTAB) as a stabilizing surfactant is commonly used to make large quantities of monodisperse gold nanorods. This method, however, has been at times difficult to reproduce in different laboratories. We recently showed [Smith, D. K.; Korgel, B. A. Langmuir 2008, 24, 644-649] that a very low concentration impurity in CTAB obtained from some suppliers prevents nanorod growth but were not able to identify the impurity. Here, we report that the impurity is iodide. Inductively coupled plasma mass spectroscopy (ICP-MS) revealed that iodide concentrations vary in CTAB from different suppliers, from less than 2.75 ppm up to 840 ppm. When CTAB with iodide concentrations greater than 50 ppm is used, nanorods do not form and the product consists entirely of spherical nanocrystals. Iodide slows the reduction of Au(III) to Au0. Iodide adsorption on Au {111} surfaces inhibits nanorod growth.

Two-photon-induced photoluminescence imaging of tumors using near-infrared excited gold nanoshells

We report strong two-photon-induced photoluminescence (TPIP) from silica/gold nanoshells (NS). We demonstrate its potential application for imaging the 3D distribution of NS in tumors using a NIR laser scanning multi-photon microscope.

Self-Assembled Simple Hexagonal AB2 Binary Nanocrystal Superlattices : SEM, GISAXS, and Defects

Binary superlattices (BSLs) of sterically stabilized, hydrophobic, large (A; 11.5 nm diameter) Fe(2)O(3) and small (B; 6.1 nm diameter) Au nanocrystals were assembled by slow evaporation of colloidal dispersions on tilted substrates. A detailed analysis of the BSL structure was carried out using transmission and scanning electron microscopy (TEM and SEM) and grazing incidence small-angle X-ray scattering (GISAXS). The BSLs were simple hexagonal (sh) AB(2) superlattices (isostructural with the compound AlB(2); space group 191, P6/mmm) of large nanocrystals occupying a simple hexagonal lattice with small nanocrystals in the interstitial spaces. SEM and GISAXS confirmed long-range order of the BSLs and GISAXS revealed that the superlattice is slightly contracted (8-12%) perpendicular to the substrate as a result of solvent drying in the deposition process. When the sh-AB(2) superlattice deposits on a (100) plane, this shrinkage occurs in the [210] direction and changes the lattice symmetry to centered orthorhombic. Additionally, nearly periodic superlattice dislocations consisting of inserted half-planes of gold nanocrystals were observed by SEM in some BSLs.

Single Gold Nanorod Detection Using Confocal Light Absorption and Scattering Spectroscopy

Gold nanorods have the potential to be employed as extremely bright molecular marker labels for fluorescence, absorption, or scattering imaging of living tissue. However, samples containing a large number of gold nanorods usually exhibit relatively wide spectral lines. This linewidth limits the use of the nanorods as effective molecular labels, since it would be rather difficult to image several types of nanorod markers simultaneously. In addition, the observed linewidth does not agree well with theoretical calculations, which predict significantly narrower absorption and scattering lines. The discrepancy could be explained by apparent broadening because of the contribution of nanorods with various sizes and aspect ratios. We measured native scattering spectra of single gold nanorods with the confocal light absorption and scattering spectroscopy system, and found that single gold nanorods have a narrow spectrum as predicted by the theory, which suggests that nanorod-based molecular markers with controlled narrow aspect ratios, and to a lesser degree size distributions, should provide spectral lines sufficiently narrow for effective biomedical imaging.

Observation of plasmon line broadening in single gold nanorods

Attempts to realize the important potential of gold nanorods as extremely bright molecular markers have been limited by the broad spectroscopic linewidths usually observed. We identify the origin of this broadening as inhomogeneous broadening due to the extreme sensitivity of the surface plasmon resonance to the nanorod aspect ratio. Using confocal light scattering spectroscopic microscopy, we observed the narrow homogeneously broadened plasmon lines of single gold nanorods and obtained the first quantitative measurements of this homogeneous broadening. We show that homogeneous broadening can be predicted from first principals.

Colloidal magnetic nanocrystals: synthesis, properties and applications

There has been a tremendous research effort in the past few years in colloidal magnetic nanocrystals. New synthetic methods have been developed that enable a wide variety of magnetic materials to be synthesized in nanocrystal form, including ferromagnetic transition metals, intermetallics and metal oxides. These nanocrystals can be obtained with controlled size, shape and composition. Nanocrystal heterostructures, such as core/shell particles and heterodimers can be synthesized. New materials such as doped magnetic semiconductor quantum dots and nanowires have been made. The magnetic properties of these unique nanostructures have been measured and their applications in medicine, information storage and processing and sensing are being developed. This review attempts to provide a summary and a flavor for this exciting research area as it has evolved during the past few years.

Gold nanorods for optimized two-photon luminescence imaging of cancerous tissue

We demonstrate the use of gold nanorods as molecularly targeted contrast agents for two-photon luminescence (TPL) imaging of cancerous cells 150 μm deep inside a tissue phantom. We synthesized gold nanorods of 50 nm x 15 nm size with a longitudinal surface plasmon resonance of 760 nm. Gold nanorods were conjugated to antibodies against epidermal growth factor receptor (EGFR) and labeled to A431 human epithelial skin cancer cells in a collagen matrix tissue phantom. Using a 1.4 NA oil immersion objective lens, we found that excitation power needed for similar emission intensity in TPL imaging of labeled cells was up to 64 times less than that needed for two-photon autofluorescence (TPAF) imaging of unlabeled cells, which would correspond to a more than 4,000 times increase in emission intensity under equal excitation energy. However, the aberrations due to refractive index mismatch of the immersion oil and the sample limit imaging depth to 75 μm. Using a 0.95 NA water immersion objective lens, we observe robust two-photon emission signal from gold nanorods in the tissue phantoms from at depths of up to 150 μm. Furthermore, the increase in excitation energy required to maintain a constant emission signal intensity as imaging depth was increased was the same in both labeled and unlabeled phantom, suggesting that at the concentrations used, the addition of gold nanorods did not appreciably increase the bulk scattering coefficient of the sample. The remarkable TPL brightness of gold nanorods in comparison to TPAF signal makes them an attractive contrast agent for early detection of cutaneous melanoma.

Two-photon luminescence imaging using a MEMS-based miniaturized probe

We present two-photon luminescence (TPL) imaging of cancer cells through a 10 times 15 times 40 mm3 miniaturized probe employing a two-axis MEMS scanning mirror and an air-core photonic crystal fiber. The combination of TPL imaging with a small probe represents a potential method of distinguishing cancerous cells in tissue for diagnosis.

Two-photon luminescence imaging of cancerous tissue using gold nanorods as bright contrast agents

We demonstrate the use of gold nanorods as molecularly targeted contrast agents for two-photon luminescence (TPL) imaging of cancerous cells 150 µm deep inside a tissue phantom. We synthesized gold nanorods of 50 nm x 15 nm size with a longitudinal surface plasmon resonance of 760 nm. Gold nanorods were conjugated to antibodies against epidermal growth factor receptor (EGFR) and labeled to A431 human epithelial skin cancer cells in a collagen matrix tissue phantom. Using a 1.4 NA oil immersion objective lens, we found that excitation power needed for similar emission intensity in TPL imaging of labeled cells was up to 64 times less than that needed for two-photon autofluorescence (TPAF) imaging of unlabeled cells, which would correspond to a more than 4,000 times increase in emission intensity under equal excitation energy. However, the aberrations due to refractive index mismatch of the immersion oil and the sample limit imaging depth to 75 µm. Using a 0.95 NA water immersion objective lens, we observe robust two-photon emission signal from gold nanorods in the tissue phantoms from at depths of up to 150 µm. Furthermore, the increase in excitation energy required to maintain a constant emission signal intensity as imaging depth was increased was the same in both labeled and unlabeled phantom, suggesting that at the concentrations used, the addition of gold nanorods did not appreciably increase the bulk scattering coefficient of the sample. The remarkable TPL brightness of gold nanorods in comparison to TPAF signal makes them an attractive contrast agent for early detection of cutaneous melanoma.

Observation of narrow spectral linewidths from single gold nanorods

Nanorods have the potential to be employed as bright molecular biomedical labels. However, nanorod samples usually exhibit relatively wide spectral lines. Using CLASS microscopy we found that single gold nanorods have a narrow spectrum.