The interest in nanoscale materials stems from the fact that new properties are acquired at this length scale and, equally important, that these properties * To whom correspondence should be addressed. Phone, 404-8940292; fax, 404-894-0294; e-mail, mostafa.el-sayed@ chemistry.gatech.edu. † Case Western Reserve UniversitysMillis 2258. ‡ Phone, 216-368-5918; fax, 216-368-3006; e-mail, burda@case.edu. § Georgia Institute of Technology. 1025 Chem. Rev. 2005, 105, 1025−1102

Chemistry and properties of nanocrystals of different shapes.

Noble metal nanoparticles are capable of confining resonant photons in such a manner as to induce coherent surface plasmon oscillation of their conduction band electrons, a phenomenon leading to two important properties. Firstly, the confinement of the photon to the nanoparticle's dimensions leads to a large increase in its electromagnetic field and consequently great enhancement of all the nanoparticle's radiative properties, such as absorption and scattering. Moreover, by confining the photon's wavelength to the nanoparticle's small dimensions, there exists enhanced imaging resolving powers, which extend well below the diffraction limit, a property of considerable importance in potential device applications. Secondly, the strongly absorbed light by the nanoparticles is followed by a rapid dephasing of the coherent electron motion in tandem with an equally rapid energy transfer to the lattice, a process integral to the technologically relevant photothermal properties of plasmonic nanoparticles. Of all the possible nanoparticle shapes, gold nanorods are especially intriguing as they offer strong plasmonic fields while exhibiting excellent tunability and biocompatibility. We begin this review of gold nanorods by summarizing their radiative and nonradiative properties. Their various synthetic methods are then outlined with an emphasis on the seed-mediated chemical growth. In particular, we describe nanorod spontaneous self-assembly, chemically driven assembly, and polymer-based alignment. The final section details current studies aimed at applications in the biological and biomedical fields.

Gold Nanorods: From Synthesis and Properties to Biological and Biomedical Applications

Gold nanoparticles (GNPs) with controlled geometrical, optical, and surface chemical properties are the subject of intensive studies and applications in biology and medicine. To date, the ever increasing diversity of published examples has included genomics and biosensorics, immunoassays and clinical chemistry, photothermolysis of cancer cells and tumors, targeted delivery of drugs and antigens, and optical bioimaging of cells and tissues with state-of-the-art nanophotonic detection systems. This critical review is focused on the application of GNP conjugates to biomedical diagnostics and analytics, photothermal and photodynamic therapies, and delivery of target molecules. Distinct from other published reviews, we present a summary of the immunological properties of GNPs. For each of the above topics, the basic principles, recent advances, and current challenges are discussed (508 references).

Gold nanoparticles in biomedical applications: recent advances and perspectives

The wide variety of core materials available, coupled with tunable surface properties, make nanoparticles an excellent platform for a broad range of biological and biomedical applications. This Review provides an introduction to nanoparticle–biomolecular interactions as well as recent applications of nanoparticles in biological sensing, delivery, and imaging of live cells and tissues.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adma.200703183

Applications of Nanoparticles in Biology

Current medical imaging technologies allow visualization of tissue anatomy in the human body at resolutions ranging from 100 micrometers to 1 millimeter. These technologies are generally not sensitive enough to detect early-stage tissue abnormalities associated with diseases such as cancer and atherosclerosis, which require micrometer-scale resolution. Here, optical coherence tomography was adapted to allow high-speed visualization of tissue in a living animal with a catheter-endoscope 1 millimeter in diameter. This method, referred to as "optical biopsy," was used to obtain cross-sectional images of the rabbit gastrointestinal and respiratory tracts at 10-micrometer resolution.

In Vivo Endoscopic Optical Biopsy with Optical Coherence Tomography

Nanoparticles for bioimaging.

Nanoparticle-based contrast agents are quickly becoming valuable and potentially transformative tools for enhancing medical diagnostics for a wide range of in-vivo imaging modalities. Compared with conventional molecular-scale contrast agents, nanoparticles (NPs) promise improved abilities for in-vivo detection and potentially enhanced targeting efficiencies through longer engineered circulation times, designed clearance pathways, and multimeric binding capacities. However, NP contrast agents are not without issues. Difficulties in minimizing batch-to-batch variations and problems with identifying and characterizing key physicochemical properties that define the in-vivo fate and transport of NPs are significant barriers to the introduction of new NP materials as clinical contrast agents. This manuscript reviews the development and application of nanoparticles and their future potential to advance current and emerging clinical bioimaging techniques. A focus is placed on the application of solid, phase-separated materials, for example metals and metal oxides, and their specific application as contrast agents for in-vivo near-infrared fluorescence (NIRF) imaging, magnetic resonance imaging (MRI), positron emission tomography (PET), computed tomography (CT), ultrasound (US), and photoacoustic imaging (PAI). Clinical and preclinical applications of NPs are identified for a broad spectrum of imaging applications, with commentaries on the future promise of these materials. Emerging technologies, for example multifunctional and theranostic NPs, and their potential for clinical advances are also discussed.

https://static.springer.com/sgw/documents/1346325/application/pdf/Nanoparticles%20as%20contrast%20agents.pdf

Nanoparticles as contrast agents for in-vivo bioimaging: current status and future perspectives

Photoacoustic tomography (PAT) is a rapidly emerging non-invasive imaging technology that integrates the merits of high optical contrast with high ultrasound resolution. The ability to quantitatively and non-invasively image nanoparticles has important implications for the development of nanoparticles as in vivo cancer diagnostic and therapeutic agents. In this study, the ability of systemically administered poly(ethylene glycol)-coated (PEGylated) gold nanoparticles as a contrast agent for in vivo tumor imaging with PAT has been evaluated. We demonstrate that gold nanoparticles (20 and 50 nm) have high photoacoustic contrast as compared to mouse tissue ex vivo. Gold nanoparticles can be visualized in mice in vivo following subcutaneous administration using PAT. Following intravenous administration of PEGylated gold nanoparticles to tumor-bearing mice, accumulation of gold nanoparticles in tumors can be effectively imaged with PAT. With gold nanoparticles as a contrast agent, PAT has important potential applications in the image guided therapy of superficial tumors such as breast cancer, melanoma and Merkel cell carcinoma.

https://iopscience.iop.org/article/10.1088/0957-4484/20/39/395102/pdf

Gold nanoparticles as a contrast agent for in vivo tumor imaging with photoacoustic tomography.

Platinum nanoparticles prepared in reverse micelles have been used as catalysts for the electron transfer reaction between hexacyanoferrate(III) and thiosulfate ions. Nanoparticles of average diameter ranging between 10 and 80 nm have been used as catalysts. The kinetic study of the catalytic reaction showed that for a fixed mass of catalyst the catalytic rate did not increase proportionately to the decrease in particle size over the whole range from 10 to 80 nm. The maximum reaction rate has been observed for average particle diameter of about 38 nm. Particles below diameter 38 nm exhibit a trend of decreasing reaction rate with the decrease in particle size, while those above diameter 38 nm show a steady decline of reaction rate with increasing size. It has been postulated that in the case of particles of average size less than 38 nm diameter, a downward shift of Fermi level with a consequent increase of band gap energy takes place. As a result, the particles require more energy to pump electrons to the adsorbed ions for the electron transfer reaction. This leads to a reduced reaction rate catalyzed by smaller particles. On the other hand, for nanoparticles above diameter 38 nm, the change of Fermi level is not appreciable. These particles exhibit less surface area for adsorption as the particle size is increased. As a result, the catalytic efficiency of the particles is also decreased with increased particle size. The activation energies for the reaction catalyzed by platinum nanoparticles of diameters 12 and 30 nm are about 18 and 4.8 kJ/mol, respectively, indicating that the catalytic efficiency of 12-nm-diameter platinum particles is less than that of particles of diameter 30 nm. Extremely slow reaction rate of uncatalyzed reaction has been manifested through a larger activation energy of about 40 kJ/mol for the reaction.

Size-dependent catalytic behavior of platinum nanoparticles on the hexacyanoferrate(III)/thiosulfate redox reaction.

DOI: 10.1002/smll.201000847 Nanoparticle-mediated, image-guided cancer therapy has tremendous promise for increasing the effi cacy of cancer treatment while reducing toxic side effects traditionally associated with treatment. Carbon nanotubes and metal-based nanomaterials are leading candidates for image-guided therapy in cancer nanotechnology. [ 1–5 ] However, limited solvent compatibility, non-biodegradability and concerns over the safety of these nanomaterials may hinder their commercialization. Here, we show that the photothermal and photoacoustic properties of polyhydroxy fullerenes [ 6 ] (PHF)—which are water-soluble, biodegradable, [ 7 ] antioxidant, [ 8–10 ] and rapidly excreted [ 11 ] —can be applied for imaging and therapy of cancer. Biodegradable PHF-containing chitosan nanoparticles provided excellent photoacoustic contrast. Tumors injected with PHF nanoparticles and exposed to near infrared laser decreased in cross-sectional area by an average of 32% within two hours of treatment, with only a blister visible 20 hours post-treatment. We anticipate that photoacoustic and photothermal properties of PHF along with their other therapeutic properties [ 12–15 ] will enable safe, non-invasive image-guided therapy of cancer with minimal side-effects. Polyhydroxy Fullerenes for Non-Invasive Cancer Imaging and Therapy

Parvesh Sharma

Papers

Nanoparticles for bioimaging.

Nanoparticles as contrast agents for in-vivo bioimaging: current status and future perspectives

Gold nanoparticles as a contrast agent for in vivo tumor imaging with photoacoustic tomography.

Size-dependent catalytic behavior of platinum nanoparticles on the hexacyanoferrate(III)/thiosulfate redox reaction.

Polyhydroxy Fullerenes for Non‐Invasive Cancer Imaging and Therapy