Recent years have witnessed many breakthroughs in research on graphene (the first two-dimensional atomic crystal) as well as a significant advance in the mass production of this material. This one-atom-thick fabric of carbon uniquely combines extreme mechanical strength, exceptionally high electronic and thermal conductivities, impermeability to gases, as well as many other supreme properties, all of which make it highly attractive for numerous applications. Here we review recent progress in graphene research and in the development of production methods, and critically analyse the feasibility of various graphene applications.

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A roadmap for graphene

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.

Nanocarriers as an emerging platform for cancer therapy

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.

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

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).

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

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)...

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

In brain cancer surgery, it is critical to achieve extensive resection without compromising adjacent healthy, non-cancerous regions. Various technological advances have made major contributions in imaging, including intraoperative magnetic imaging (MRI) and computed tomography (CT). However, these technologies have pros and cons in providing quantitative, real-time and three-dimensional (3D) continuous guidance in brain cancer detection. Optical Coherence Tomography (OCT) is a non-invasive, label-free, cost-effective technique capable of imaging tissue in three dimensions and real time. The purpose of this study is to reliably and efficiently discriminate between non-cancer and cancer-infiltrated brain regions using OCT images. To this end, a mathematical model for quantitative evaluation known as the Blind End- Member and Abundances Extraction method (BEAE). This BEAE method is a constrained optimization technique which extracts spatial information from volumetric OCT images. Using this novel method, we are able to discriminate between cancerous and non-cancerous tissues and using logistic regression as a classifier for automatic brain tumor margin detection. Using this technique, we are able to achieve excellent performance using an extensive cross-validation of the training dataset (sensitivity 92.91% and specificity 98.15%) and again using an independent, blinded validation dataset (sensitivity 92.91% and specificity 86.36%). In summary, BEAE is well-suited to differentiate brain tissue which could support the guiding surgery process for tissue resection.

Detection of brain tumor margins using optical coherence tomography

An OCT balloon imaging catheter was developed using small compound rod lenses to achieve superb lateral resolution at a large working distance. The balloon catheter enables systematic assessment of human esophagus for Barrett's screening.

High-resolution OCT Balloon Catheter for Systematic Imaging of the Esophagus

We present a fully integrated fiber-optic scanning endomicroscope of a probe head weight less than 1.2g. Significant improvements on nonlinear signal collection efficiency (by 30 fold) and resolution (by 2 fold) have been recently achieved.

Scanning Fiber-optic Nonlinear Endomicroscopy

The authors describe a near-infrared imaging instrument capable of providing spectroscopic information over a spatially localized region of the brain. This regional imager is a frequency domain, multiwavelength (779 and 834 nm) system with multiple source (12) and detector (4) positions. The modulation frequency is selectable, ranging from 50 to over 400 MHz. The regional imager offers the possibility for reconstruction of optical properties with linear resolutions of /spl sim/1 cm, beneath an area of /spl sim/40 cm/sup 2/ in size, within a short period of time (3 min). Clinical applications include evaluation of critical care conditions such as hydrocephalus and hematoma, as well as monitoring blood oxygenation during heart surgery and cognition studies. For real-time analysis of a measurement, the authors use a backprojection algorithm to reconstruct images. In the authors' backprojection approach, they derive an absorption coefficient /spl mu//sub s/ and scattering coefficient /spl mu//sub s/' for each source-detector pair by numerically solving the semi-infinite solution for the values of /spl mu//sub s/ and /spl mu//sub s/' using the measurements from the source-detector pair. These values are then back-projected using weights that are essentially the three-point Green's function. The authors are currently investigating use of the Rytov approximation for image reconstruction in a reflectance geometry.

Near infrared imaging of brains

Summary form only given. Optical coherence tomography (OCT) has been extensively investigated as a diagnostic tool in a variety of medical fields, demonstrating its feasibility as a high speed, non-invasive, high resolution in vivo and in situ imaging modality. Typical OCT systems require a mechanically translating reference arm mirror to achieve axial scanning. Scan velocities for galvonometer based scanning systems are limited by mechanical inertia to approximately 3 cm/s with repetition rates of /spl sim/100 Hz. In order to remove motion artifact for imaging in vivo, image acquisition rates of several frames per second are necessary. We demonstrate a simple, low cost, alternative scanning delay line capable of scanning over several millimeters at 2 kHz repetition frequency. The system uses a multi-pass mirror geometry based on a Herriott type cell, which accumulates differential delays in each pass.

Xingde Li

Papers

Detection of brain tumor margins using optical coherence tomography

High-resolution OCT Balloon Catheter for Systematic Imaging of the Esophagus

Scanning Fiber-optic Nonlinear Endomicroscopy

Near infrared imaging of brains

High-speed path length scanning using a Herriott cell delay line