Hu Cang

Bio: Hu Cang is an academic researcher from Salk Institute for Biological Studies. The author has contributed to research in topics: Nanocages & Liquid crystal. The author has an hindex of 32, co-authored 53 publications receiving 4221 citations. Previous affiliations of Hu Cang include Lawrence Berkeley National Laboratory & University of California, Berkeley.

Gold nanocages: bioconjugation and their potential use as optical imaging contrast agents.

Abstract: Gold nanocages of <40 nm in dimension have been synthesized using the galvanic replacement reaction between Ag nanocubes and HAuCl4 in an aqueous solution. By controlling the molar ratio between Ag and HAuCl4, the gold nanocages could be tuned to display surface plasmon resonance peaks around 800 nm, a wavelength commonly used in optical coherence tomography (OCT) imaging. OCT measurements on phantom samples indicate that these gold nanocages have a moderate scattering cross-section of ∼8.10 × 10-16 m2 but a very large absorption cross-section of ∼7.26 × 10-15 m2, suggesting their potential use as a new class of contrast agents for optical imaging. When bioconjugated with antibodies, the gold nanocages have also been demonstrated for specific targeting of breast cancer cells.

Gold Nanocages: Engineering Their Structure for Biomedical Applications

Abstract: The galvanic replacement reaction between a Ag template and HAuCl4 in an aqueous solution transforms 30-200 mn Ag nanocubes into Au nanoboxes and nanocages (nanoboxes with porous walls). By controlling the molar ratio of Ag to HAuCl4, the extinction peak of resultant structures can be continuously tuned from the blue (400 nm) to the near-infrared (1200 nm) region of the electromagnetic spectrum. These hollow An nanostructures are characterized by extraordinarily large cross sections for both absorption and scattering. Optical coherence tomography measurements indicate that the 36 nm nanocage has a scattering cross-section of similar to 0.8 X 10(-15) m(2) and an absorption cross-section of similar to 7.3 X 10(-15) m(2). The absorption cross-section is more than five orders of magnitude larger than those of conventional organic dyes. Exposure of Au nanocages to a camera flash resulted in the melting and conversion of Au nanocages into spherical particles due to photothermal heating. Discrete-di poleapproximation calculations suggest that the magnitudes of both scattering and absorption cross-sections of An nanocages can be tailored by controlling their dimensions, as well as the thickness and porosity of their walls. This novel class of hollow nanostructures is expected to find use as both a contrast agent for optical imaging in early stage tumor detection and as a therapeutic agent for photothermal cancer treatment.

Shape-Controlled Synthesis of Silver and Gold Nanostructures

Abstract: This article provides a brief account of solution-phase methods that generate silver and gold nanostructures with well-controlled shapes. It is organized into five sections: The first section discusses the nucleation and formation of seeds from which nanostructures grow. The next two sections explain how seeds with fairly isotropic shapes can grow anisotropically into distinct morphologies. Polyol synthesis is selected as an example to illustrate this concept. Specifically, we discuss the growth of silver nanocubes (with and without truncated corners), nanowires, and triangular nanoplates. In the fourth section, we show that silver nanostructures can be transformed into hollow gold nanostructures through a galvanic replacement reaction. Examples include nanoboxes, nanocages, nanotubes (both single- and multi-walled), and nanorattles. The fifth section briefly outlines a potential medical application for gold nanocages.We conclude with some perspectives on areas for future work.

Probing the electromagnetic field of a 15-nanometre hotspot by single molecule imaging

Abstract: It is well known that hotspots can appear on rough metallic surfaces exposed to light, where the incident light is concentrated on the nanometre scale to produce an intense electromagnetic field. This 'surface enhancement' effect can be used, for example, to detect molecules, because weak fluorescence signals are strongly enhanced by the hotspots. Such hotspots are associated with localized electromagnetic modes, caused by the randomness of the surface texture, but the detailed profile of the local electromagnetic field is so far unknown. Cang et al. now describe an ingenious experiment that exploits the Brownian motion of single molecules to probe the local field. They succeed in imaging the fluorescence enhancement profile of single hotspots on the surface of aluminium thin-film and silver nanoparticle clusters with accuracy down to 1 nm, and find that the field distribution in a hotspot follows an exponential decay. On rough metallic surfaces hotspots appear under optical illumination that concentrate light to tens of nanometres. This effect can be used to detect molecules, as weak fluorescence signals are strongly enhanced by the hotspots. Such hotspots are associated with localized electromagnetic modes, caused by the randomness of the surface texture, but the detailed profile of the local electromagnetic field is unknown. Here, an ingenious approach is described, making use of the Brownian motion of single molecules to probe the local field. The study succeeds in imaging the fluorescence enhancement profile of single hotspots on the surface of aluminium thin-film and silver nanoparticle clusters with accuracy down to one nanometre, and finds that the field distribution in a hotspot follows an exponential decay. When light illuminates a rough metallic surface, hotspots can appear, where the light is concentrated on the nanometre scale, producing an intense electromagnetic field. This phenomenon, called the surface enhancement effect1,2, has a broad range of potential applications, such as the detection of weak chemical signals. Hotspots are believed to be associated with localized electromagnetic modes3,4, caused by the randomness of the surface texture. Probing the electromagnetic field of the hotspots would offer much insight towards uncovering the mechanism generating the enhancement; however, it requires a spatial resolution of 1–2 nm, which has been a long-standing challenge in optics. The resolution of an optical microscope is limited to about half the wavelength of the incident light, approximately 200–300 nm. Although current state-of-the-art techniques, including near-field scanning optical microscopy5, electron energy-loss spectroscopy6, cathode luminescence imaging7 and two-photon photoemission imaging8 have subwavelength resolution, they either introduce a non-negligible amount of perturbation, complicating interpretation of the data, or operate only in a vacuum. As a result, after more than 30 years since the discovery of the surface enhancement effect9,10,11, how the local field is distributed remains unknown. Here we present a technique that uses Brownian motion of single molecules to probe the local field. It enables two-dimensional imaging of the fluorescence enhancement profile of single hotspots on the surfaces of aluminium thin films and silver nanoparticle clusters, with accuracy down to 1.2 nm. Strong fluorescence enhancements, up to 54 and 136 times respectively, are observed in those two systems. This strong enhancement indicates that the local field, which decays exponentially from the peak of a hotspot, dominates the fluorescence enhancement profile.

Gold nanocages as contrast agents for spectroscopic optical coherence tomography.

Abstract: We describe gold nanocages as a new class of potential contrast agent for spectroscopic optical coherence tomography (OCT). Monodispersed gold nanocages of an approximately 35 nm edge length exhibit strong optical resonance, with the peak wavelength tunable in the near-infrared range. We characterized the optical properties of the nanocage by using OCT experiments along with numerical calculations, revealing an absorption cross section approximately 5 orders of magnitude larger than conventional dyes. Experiments with tissue phantoms demonstrated that the nanocages provide enhanced contrast for spectroscopic as well as conventional intensity-based OCT imaging.

Nanocarriers as an emerging platform for cancer therapy

Abstract: Nanotechnology has the potential to revolutionize cancer diagnosis and therapy. Advances in protein engineering and materials science have contributed to novel nanoscale targeting approaches that may bring new hope to cancer patients. Several therapeutic nanocarriers have been approved for clinical use. However, to date, there are only a few clinically approved nanocarriers that incorporate molecules to selectively bind and target cancer cells. This review examines some of the approved formulations and discusses the challenges in translating basic research to the clinic. We detail the arsenal of nanocarriers and molecules available for selective tumour targeting, and emphasize the challenges in cancer treatment.

Shape‐Controlled Synthesis of Metal Nanocrystals: Simple Chemistry Meets Complex Physics?

Abstract: Nanocrystals are fundamental to modern science and technology. Mastery over the shape of a nanocrystal enables control of its properties and enhancement of its usefulness for a given application. Our aim is to present a comprehensive review of current research activities that center on the shape-controlled synthesis of metal nanocrystals. We begin with a brief introduction to nucleation and growth within the context of metal nanocrystal synthesis, followed by a discussion of the possible shapes that a metal nanocrystal might take under different conditions. We then focus on a variety of experimental parameters that have been explored to manipulate the nucleation and growth of metal nanocrystals in solution-phase syntheses in an effort to generate specific shapes. We then elaborate on these approaches by selecting examples in which there is already reasonable understanding for the observed shape control or at least the protocols have proven to be reproducible and controllable. Finally, we highlight a number of applications that have been enabled and/or enhanced by the shape-controlled synthesis of metal nanocrystals. We conclude this article with personal perspectives on the directions toward which future research in this field might take.

Integrative analysis of 111 reference human epigenomes

Abstract: The reference human genome sequence set the stage for studies of genetic variation and its association with human disease, but epigenomic studies lack a similar reference. To address this need, the NIH Roadmap Epigenomics Consortium generated the largest collection so far of human epigenomes for primary cells and tissues. Here we describe the integrative analysis of 111 reference human epigenomes generated as part of the programme, profiled for histone modification patterns, DNA accessibility, DNA methylation and RNA expression. We establish global maps of regulatory elements, define regulatory modules of coordinated activity, and their likely activators and repressors. We show that disease- and trait-associated genetic variants are enriched in tissue-specific epigenomic marks, revealing biologically relevant cell types for diverse human traits, and providing a resource for interpreting the molecular basis of human disease. Our results demonstrate the central role of epigenomic information for understanding gene regulation, cellular differentiation and human disease.

Determining the size and shape dependence of gold nanoparticle uptake into mammalian cells.

Abstract: We investigated the intracellular uptake of different sized and shaped colloidal gold nanoparticles. We showed that kinetics and saturation concentrations are highly dependent upon the physical dimensions of the nanoparticles (e.g., uptake half-life of 14, 50, and 74 nm nanoparticles is 2.10, 1.90, and 2.24 h, respectively). The findings from this study will have implications in the chemical design of nanostructures for biomedical applications (e.g., tuning intracellular delivery rates and amounts by nanoscale dimensions and engineering complex, multifunctional nanostructures for imaging and therapeutics).

Calculated Absorption and Scattering Properties of Gold Nanoparticles of Different Size, Shape, and Composition: Applications in Biological Imaging and Biomedicine

Abstract: The selection of nanoparticles for achieving efficient contrast for biological and cell imaging applications, as well as for photothermal therapeutic applications, is based on the optical properties of the nanoparticles. We use Mie theory and discrete dipole approximation method to calculate absorption and scattering efficiencies and optical resonance wavelengths for three commonly used classes of nanoparticles: gold nanospheres, silica−gold nanoshells, and gold nanorods. The calculated spectra clearly reflect the well-known dependence of nanoparticle optical properties viz. the resonance wavelength, the extinction cross-section, and the ratio of scattering to absorption, on the nanoparticle dimensions. A systematic quantitative study of the various trends is presented. By increasing the size of gold nanospheres from 20 to 80 nm, the magnitude of extinction as well as the relative contribution of scattering to the extinction rapidly increases. Gold nanospheres in the size range commonly employed (∼40 nm)...