All-optical nanoscale pH meter.

We show that an Au nanoshell with a pH-sensitive molecular adsorbate functions as a standalone, all-optical nanoscale pH meter that monitors its local environment through the pH-dependent surface-enhanced Raman scattering (SERS) spectra of the adsorbate molecules. Moreover, we also show how the performance of such a functional nanodevice can be assessed quantitatively. The complex spectral output is reduced to a simple device characteristic by application of a locally linear manifold approximation algorithm.

Cu nanoshells: effects of interband transitions on the nanoparticle plasmon resonance.

The optical properties of metals arise both from optical excitation of interband transitions and their collective electronic, or plasmon, response. Here, we examine the optical properties of Cu, whose strong interband transitions dominate its optical response in the visible region of the spectrum, in a nanoshell geometry. This nanostructure permits the geometrical tuning of the nanoparticle plasmon energy relative to the onset of interband transitions in the metal.

Controlled texturing modifies the surface topography and plasmonic properties of Au nanoshells.

We report a facile and controllable method for the postfabrication texturing of the surface topography of Au nanoshells based on site-selective chemical etching of the polycrystalline Au nanoshell surface by a bifunctional alkanethiol molecule, cysteamine. This nanoscale surface texturing process systematically introduces dramatic changes to the plasmonic properties of the Au nanoshells. The modification of the plasmon resonant properties of nanoshells as a function of increased surface roughness was examined experimentally and modeled theoretically using three-dimensional finite difference time domain (FDTD) simulations.

Symmetry breaking in individual plasmonic nanoparticles.

The plasmon resonances of a concentric metallic nanoshell arise from the hybridization of primitive plasmon modes of the same angular momentum on its inner and outer surfaces. For a nanoshell with an offset core, the reduction in symmetry relaxes these selection rules, allowing for an admixture of dipolar components in all plasmon modes of the particle. This metallodielectric nanostructure with reduced symmetry exhibits a core offset-dependent multipeaked spectrum, seen in single-particle spectroscopic measurements, and exhibits significantly larger local-field enhancements on its external surface than the equivalent concentric spherical nanostructure.

Determining the conformation of thiolated poly(ethylene glycol) on Au nanoshells by surface-enhanced Raman scattering spectroscopic assay.

The packing density of thiolated poly(ethylene glycol) (PEG) adsorbates on Au nanoshells is determined by exploiting the surface-enhanced Raman scattering response of individual nanoshell substrates. By incorporating the linker molecule p-mercaptoaniline (pMA), the number of 2000 MW and 5000 MW PEG molecules on each nanoparticle is determined by interpolation of the Langmuir isotherm for pMA. We conclude that both PEG adsorbates maintain a compact "brush" rather than an extended "mushroom" configuration on nanoshell surfaces.

Nanorice: a hybrid plasmonic nanostructure.

We have designed and fabricated a new hybrid nanoparticle that combines the intense local fields of nanorods with the highly tunable plasmon resonances of nanoshells. This dielectric core-metallic shell prolate spheroid nanoparticle bears a remarkable resemblance to a grain of rice, inspiring the name "nanorice". This geometry possesses far greater structural tunability than either a nanorod or a nanoshell, along with much larger local field intensity enhancements and far greater sensitivity as a surface plasmon resonance (SPR) nanosensor than any dielectric-metal nanostructures reported previously.

Metal nanoshells.

Metal nanoshells are a new class of nanoparticles with highly tunable optical properties. Metal nanoshells consist of a dielectric core nanoparticle such as silica surrounded by an ultrathin metal shell, often composed of gold for biomedical applications. Depending on the size and composition of each layer of the nanoshell, particles can be designed to either absorb or scatter light over much of the visible and infrared regions of the electromagnetic spectrum, including the near infrared region where penetration of light through tissue is maximal.

Optically tunable nanoparticle contrast agents for early cancer detection: model-based analysis of gold nanoshells.

Many optical diagnostic approaches rely on changes in scattering and absorption properties to generate optical contrast between normal and diseased tissue. Recently, there has been increasing interest in using exogenous agents to enhance this intrinsic contrast with particular emphasis on the development for targeting specific molecular features of disease. Gold nanoshells are a class of core-shell nanoparticles with an extremely tunable peak optical resonance ranging from the near-UV to the mid-IR wavelengths.

Nanosphere arrays with controlled sub-10-nm gaps as surface-enhanced raman spectroscopy substrates.

We demonstrate a convenient and cost-effective chemical approach for fabricating highly ordered Au nanoparticle arrays with sub-10-nm interparticle gaps. Near-field enhancements inside the interparticle gaps create uniform periodic arrays of well-defined "hot spots" exploitable for large surface-enhanced Raman spectroscopy (SERS) enhancements. A cetyltrimethylammonium bromide (CTAB) bilayer surrounding each individual nanoparticle upon array crystallization is responsible for this periodic gap structure; displacement of the CTAB by smaller thiolated molecules does not affect the structural integrity of the arrays.

Plasmons in the metallic nanoparticle-film system as a tunable impurity problem.

We show that the plasmon resonances of a metallic nanoparticle interacting with the surface plasmons of a metallic film is an electromagnetic analogue of the spinless Anderson-Fano model. This is the same model used to describe the interaction of a localized electronic state with a continuous band of electronic states. The three characteristic regimes of this model are realized here, where the energy of the nanoparticle plasmon resonance lies above, within, or below the energy band of surface plasmon states.

Surface-enhanced Raman scattering from individual au nanoparticles and nanoparticle dimer substrates.

Surface-enhanced Raman scattering (SERS) intensities for individual Au nanospheres, nanoshells, and nanosphere and nanoshell dimers coated with nonresonant molecules are measured, where the precise nanoscale geometry of each monomer and dimer is identified through in situ atomic force microscopy. The observed intensities correlate with the integrated quartic local electromagnetic field calculated for each specific nanostructure geometry. In this study, we find that suitably fabricated nanoshells can provide SERS enhancements comparable to nanosphere dimers.

Near infrared laser-tissue welding using nanoshells as an exogenous absorber.

Background And Objective: Gold nanoshells are a new class of nanoparticles that can be designed to strongly absorb light in the near infrared (NIR). These particles provide much larger absorption cross-sections and efficiency than can be achieved with currently used chemical chromophores without photobleaching. In these studies, we have investigated the use of gold nanoshells as exogenous NIR absorbers to facilitate NIR laser-tissue welding.

Independent Optical Control of Microfluidic Valves Formed from Optomechanically Responsive Nanocomposite Hydrogels.

Independent optical control of microfluidic valves formed from optomechanically responsive nanocomposite hydrogels is achieved using strongly absorbing Au nanoparticles or nanoshells embedded within a thermally responsive polymer. Valves formed from composites with different nanoparticles could be independently controlled by changing the illumination wavelength.

Whole-blood immunoassay facilitated by gold nanoshell-conjugate antibodies.

In this chapter, we outline a simple procedure using gold nanoshells as a substrate for an immunoassay that is capable of detecting subnanogram levels of analyte within whole blood on the order of minutes. Unique to metallic nanoshells is their optical tunability over a large range of wavelengths. We describe the design of nanoshells that attenuate light strongly in a region of light where blood does not (i.

Gold nanoshell bioconjugates for molecular imaging in living cells.

Advances in scattering-based optical imaging technologies offer a new approach to noninvasive point-of-care detection, diagnosis, and monitoring of cancer. Emerging photonics technologies provide a cost-effective means to image tissue in vivo with high resolution in real time. Advancing the clinical potential of these imaging strategies requires the development of optical contrast agents targeted to specific molecular signatures of disease.

Immunotargeted nanoshells for integrated cancer imaging and therapy.

Nanoshells are a novel class of optically tunable nanoparticles that consist of a dielectric core surrounded by a thin gold shell. Based on the relative dimensions of the shell thickness and core radius, nanoshells may be designed to scatter and/or absorb light over a broad spectral range including the near-infrared (NIR), a wavelength region that provides maximal penetration of light through tissue. The ability to control both wavelength-dependent scattering and absorption of nanoshells offers the opportunity to design nanoshells which provide, in a single nanoparticle, both diagnostic and therapeutic capabilities.

Fluorinated nanodiamond as a wet chemistry precursor for diamond coatings covalently bonded to glass surface.

The chemical reaction between fluoro-nanodiamond (F-ND) powder, solubilized in o-dichlorobenzene, and a glass surface, functionalized with the silane coupling agent, 3-aminopropyltriethoxysilane (APTES), was found to proceed under heating at 130 degrees C for 24-40 h and to result in covalent bonding of F-ND particles to a glass substrate, forming a 10-40 nm thick nanocrystalline film. The observed process presents a novel and cost-effective approach to fabrication of diamond coatings on glass by using wet chemistry instead of CVD and can be extended to other materials.

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.

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.

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.

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

Metal nanoshells are a class of nanoparticles with tunable optical resonances. In this article, an application of this technology to thermal ablative therapy for cancer is described. By tuning the nanoshells to strongly absorb light in the near infrared, where optical transmission through tissue is optimal, a distribution of nanoshells at depth in tissue can be used to deliver a therapeutic dose of heat by using moderately low exposures of extracorporeally applied near-infrared (NIR) light.

A hybridization model for the plasmon response of complex nanostructures.

We present a simple and intuitive picture, an electromagnetic analog of molecular orbital theory, that describes the plasmon response of complex nanostructures of arbitrary shape. Our model can be understood as the interaction or "hybridization" of elementary plasmons supported by nanostructures of elementary geometries. As an example, the approach is applied to the important case of a four-layer concentric nanoshell, where the hybridization of the plasmons of the inner and outer nanoshells determines the resonant frequencies of the multilayer nanostructure.

Engineered nanomaterials for biophotonics applications: improving sensing, imaging, and therapeutics.

Advances in chemistry and physics are providing an expanding array of nanostructured materials with unique and powerful optical properties. These nanomaterials provide a new set of tools that are available to biomedical engineers, biologists, and medical scientists who seek new tools as biosensors and probes of biological fluids, cells, and tissue chemistry and function. Nanomaterials are also being used to develop optically controlled devices for applications such as modulated drug delivery as well as optical therapeutics.

A whole blood immunoassay using gold nanoshells.

A rapid immunoassay capable of detecting analyte within complex biological media without any sample preparation is described. This was accomplished using gold nanoshells, layered dielectric-metal nanoparticles whose optical resonance is a function of the relative size of its constituent layers. Aggregation of antibody/nanoshell conjugates with extinction spectra in the near-infrared was monitored spectroscopically in the presence of analyte.

Applications of nanotechnology to biotechnology commentary.

The ability to systematically modify the properties of nanostructures by controlling their structure and their surface properties at a nanoscale level makes them extremely attractive candidates for use in biological contexts, from fundamental scientific studies to commercially viable technologies.