Nanoshell-mediated near-infrared thermal therapy of tumors under magnetic resonance guidance

Surface-enhanced Raman scattering on tunable plasmonic nanoparticle substrates

Au and Ag nanoshells are investigated as substrates for surface-enhanced Raman scattering (SERS). We find that SERS enhancements on nanoshell films are dramatically different from those observed on colloidal aggregates, specifically that the Raman enhancement follows the plasmon resonance of the individual nanoparticles. Comparative finite difference time domain calculations of fields at the surface of smooth and roughened nanoshells reveal that surface roughness contributes only slightly to the total enhancement. SERS enhancements as large as 2.5 x 10(10) on Ag nanoshell films for the nonresonant molecule p-mercaptoaniline are measured.

Quantum dots and other nanoparticles: what can they offer to drug discovery?

Nanocrystals (quantum dots) and other nanoparticles (gold colloids, magnetic bars, nanobars, dendrimers and nanoshells) have been receiving a lot of attention recently with their unique properties for potential use in drug discovery, bioengineering and therapeutics. In this review, structural, optical and biological assets of nanocrystals are summarized and their applications to drug discovery studies are discussed. Unique properties of these nanoparticles can offer new advancements in drug discovery.

Intracellular pH Sensors Based on Surface-Enhanced Raman Scattering

We present the development of nanoscale pH sensors based on functionalized silver nanoparticles and surface-enhanced Raman scattering (SERS). The SERS spectrum from individual silver nanoparticle (50-80 nm in diameter) clusters functionalized with 4-mercaptobenzoic acid shows a characteristic response to the pH of the surrounding solution and is sensitive to pH changes in the range of 6-8. Measurements from nanoparticles incorporated in living Chinese hamster ovary cells demonstrate that the nanoparticle sensors retain their robust signal and sensitivity to pH when incorporated into a cell.

Semiconductor quantum dots as contrast agents for whole animal imaging

Recent developments in quantum dot (QD) technology have paved the way for using QDs as optical contrast agents for in vivo imaging. Pioneering papers showed the use of QDs as luminescent contrast agents for imaging cancer and guiding cancer surgery. The possible future use of QDs for clinical applications is expected to have a significant impact, however many challenges in this field have yet to be overcome.

Electronic structure and bonding of Au on a SiO2 cluster: a nanobullet for tumors

The binding of gold atoms to a small silica cluster has been studied by using density functional theory with generalized gradient approximation for exchange and correlation. It is shown that gold atoms bind to silicon atoms with dangling bonds and serve as seeds for the growth of Au islands. The large electron affinity of gold causes a significant change in the electronic structure of silica resulting in a substantial reduction in the highest occupied and the lowest unoccupied molecular orbital and the optical gap, thus allowing it to absorb near infrared radiation. This suggests that a small cluster can have a similar functionality in the treatment of cancer as the large size nanoshell, but for a different mechanism.

Nanotechnology and Tumor Imaging: Seizing an Opportunity

Nanoparticles, labeled with a signaling moiety for in vivo imaging, and one or more ligands for molecularly targeted specificity, hold considerable promise in oncology. Nanoparticles can serve as modular platforms, from which a wide variety of highly sensitive and specific imaging agents can be created. For example, many hundreds or thousands of atoms that provide imaging signals, such as radioisotopes, lanthanides, or fluorophores, can be attached to each nanoparticle, to form imaging agents that would provide higher sensitivity that can be obtained from agents based on small molecules. Similarly, many copies of targeted ligands can be attached to nanoparticles to markedly increase specific binding. Drugs or therapeutic isotopes can be added to create multifunctional nanoparticles. Appropriately labeled and targeted nanoparticles could lead to a paradigm change in which cancer detection, diagnosis, and therapy are combined in a single molecular complex.

A New Route to Obtain Shape-Controlled Gold Nanoparticles from Au(III)-β-diketonates

Ligands with a beta-diketone skeleton have been employed for the first time as reductant to produce ligand stabilized gold nanoparticles of different shapes from aqueous HAuCl(4) solution. Evolution of stable gold nanoparticles follows first order (k approximately equal to 10(-2) min(-1)) kinetics with respect to Au(0) concentration. Growth of particles of different shapes (spherical or triangular or hexagonal) goes hand in hand under the influence of different beta-diketones, which have excellent capping and reducing properties. Chlorine insertion was observed to take place in the beta-diketone skeleton.

Photo-thermal tumor ablation in mice using near infrared-absorbing nanoparticles

The following study examines the feasibility of nanoshell-assisted photo-thermal therapy (NAPT). This technique takes advantage of the strong near infrared (NIR) absorption of nanoshells, a new class of gold nanoparticles with tunable optical absorptivities that can undergo passive extravasation from the abnormal tumor vasculature due to their nanoscale size. Tumors were grown in immune-competent mice by subcutaneous injection of murine colon carcinoma cells (CT26.WT). Polyethylene glycol (PEG) coated nanoshells (approximately 130 nm diameter) with peak optical absorption in the NIR were intravenously injected and allowed to circulate for 6 h. Tumors were then illuminated with a diode laser (808 nm, 4 W/cm2, 3 min). All such treated tumors abated and treated mice appeared healthy and tumor free >90 days later. Control animals and additional sham-treatment animals (laser treatment without nanoshell injection) were euthanized when tumors grew to a predetermined size, which occurred 6-19 days post-treatment. This simple, non-invasive procedure shows great promise as a technique for selective photo-thermal tumor ablation.

Biological synthesis of triangular gold nanoprisms

The optoelectronic and physicochemical properties of nanoscale matter are a strong function of particle size. Nanoparticle shape also contributes significantly to modulating their electronic properties. Several shapes ranging from rods to wires to plates to teardrop structures may be obtained by chemical methods; triangular nanoparticles have been synthesized by using a seeded growth process. Here, we report the discovery that the extract from the lemongrass plant, when reacted with aqueous chloroaurate ions, yields a high percentage of thin, flat, single-crystalline gold nanotriangles. The nanotriangles seem to grow by a process involving rapid reduction, assembly and room-temperature sintering of 'liquid-like' spherical gold nanoparticles. The anisotropy in nanoparticle shape results in large near-infrared absorption by the particles, and highly anisotropic electron transport in films of the nanotriangles.

Nanoshell-enabled photonics-based imaging and therapy of cancer

Metal nanoshells are a novel type of composite spherical nanoparticle consisting of a dielectric core covered by a thin metallic shell which is typically gold. Nanoshells possess highly favorable optical and chemical properties for biomedical imaging and therapeutic applications. By varying the relative the dimensions of the core and the shell, the optical resonance of these nanoparticles can be precisely and systematically varied over a broad region ranging from the near-UV to the mid-infrared. This range includes the near-infrared (NIR) wavelength region where tissue transmissivity peaks. In addition to spectral tunability, nanoshells offer other advantages over conventional organic dyes including improved optical properties and reduced susceptibility to chemical/thermal denaturation. Furthermore, the same conjugation protocols used to bind biomolecules to gold colloid are easily modified for nanoshells. In this article, we first review the synthesis of gold nanoshells and illustrate how the core/shell ratio and overall size of a nanoshell influences its scattering and absorption properties. We then describe several examples of nanoshell-based diagnostic and therapeutic approaches including the development of nanoshell bioconjugates for molecular imaging, the use of scattering nanoshells as contrast agents for optical coherence tomography (OCT), and the use of absorbing nanoshells in NIR thermal therapy of tumors.

Mechanistic Study on the Replacement Reaction between Silver Nanostructures and Chloroauric Acid in Aqueous Medium

The replacement reaction between silver nanostructures and an aqueous HAuCl(4) solution has recently been demonstrated as a versatile method for generating metal nanostructures with hollow interiors. Here we describe the results of a systematic study detailing the morphological, structural, compositional, and spectral changes involved in such a heterogeneous reaction on the nanoscale. Two distinctive steps have been resolved through a combination of microscopic and spectroscopic methods. In the first step, silver nanostructure (i.e., the template) is dissolved to generate gold atoms that are deposited epitaxially on the surface of each template. Silver atoms also diffuse into the gold shell (or sheath) to form a seamless, hollow nanostructure with its wall made of Au-Ag alloys. The second step involves dealloying, a process that selectively removes silver atoms from the alloyed wall, induces morphological reconstruction, and finally leads to the formation of pinholes in the walls. Reaction temperature was found to play an important role in the replacement reaction because the solubility constant of AgCl and the diffusion coefficients of Ag and Au atoms were both strongly dependent on this parameter. This work has enabled us to prepare metal nanostructures with controllable geometric shapes and structures, and thus optical properties (for example, the surface plasmon resonance peaks could be readily shifted from 500 to 1200 nm by controlling the ratio between Ag and HAuCl(4)).

Reversible generation of gold nanoparticle aggregates with changeable interparticle interactions by UV photoactivation

Evolution of exclusively spherical tiny gold nanoparticle aggregates is reported by UV photoactivation of aqueous HAuCl4 solution in cetyltrimethylammonium chloride micelles. In the photoactivation process, citrate is introduced for the first time to obtain aggregates of interacting particles with a tight size distribution. It is seen that the spectrum is substantially altered from the usual Au plasma resonance while the particles are present in the aggregate. Due to the interparticle interaction, the solution renders a blue color. Blue-pink color transformation of the gold sol has been observed in relation to the change in the interparticle distances without any change in the aspect ratio of the particles.