Showing papers in "Small in 2008"

Cytotoxicity of Nanoparticles

Abstract: Human exposure to nanoparticles is inevitable as nanoparticles become more widely used and, as a result, nanotoxicology research is now gaining attention. However, while the number of nanoparticle types and applications continues to increase, studies to characterize their effects after exposure and to address their potential toxicity are few in comparison. In the medical field in particular, nanoparticles are being utilized in diagnostic and therapeutic tools to better understand, detect, and treat human diseases. Exposure to nanoparticles for medical purposes involves intentional contact or administration; therefore, understanding the properties of nanoparticles and their effect on the body is crucial before clinical use can occur. This Review presents a summary of the in vitro cytotoxicity data currently available on three classes of nanoparticles. With each of these nanoparticles, different data has been published about their cytotoxicity due to varying experimental conditions as well as differing nanoparticle physiochemical properties. For nanoparticles to move into the clinical arena, it is important that nanotoxicology research uncovers and understands how these multiple factors influence the toxicity of nanoparticles so that their undesirable properties can be avoided.

Shape Control of Colloidal Metal Nanocrystals

Abstract: Colloidal metal nanoparticles are emerging as key materials for catalysis, plasmonics, sensing, and spectroscopy. Within these applications, control of nanoparticle shape lends increasing functionality and selectivity. Shape-controlled nanocrystals possess well-defined surfaces and morphologies because their nucleation and growth are controlled at the atomic level. An overall picture of shaped metal particles is presented, with a particular focus on solution-based syntheses for the noble metals. General strategies for synthetic control are discussed, emphasizing key factors that result in anisotropic, nonspherical growth such as crystallographically selective adsorbates and seeding processes.

Surface functionalized carbogenic quantum dots.

Abstract: Quantum dots are semiconductor nanocrystals that inherently fluoresce at specific wavelengths in the visible, enabling a number of potential applications to be realized. However, conventional quantum dots are based on metallic elements, which has raised concerns over toxicity, stability and high cost. As a result, the search for more benign substitutes is a worthwhile yet challenging undertaking. Recently a new type of visible emitters has been reported exclusively based on functionalized carbon nanoparticles. The carbon dots were 5 nm in diameter and were produced via laser ablation of graphite. Surface oxidation with nitric acid and subsequent covalent grafting of organic moieties afforded light-emitting derivatives. Notably, the light emitted by these dots depends on the wavelength of light used for excitation. It was suggested that the tethered modifier stabilizes the surface of the carbon nanoparticles helping to generate energy traps that emit light when stimulated, an effect described as emission from passivated surfaces. Because of its origin the emission is size-dependent, i.e., the smaller the size of the dots the better their photoluminescence efficiency. In another intriguing approach, photoluminescent carbon dots 3 nm in size were directly fabricated by electrochemical shocking of multi-wall carbon nanotubes. The demonstrated photoluminescence adds another dimension to the versatility of carbon-based

Nanostructured Surfaces and Assemblies as SERS Media

Abstract: Metallic nanostructures attract much interest as an efficient media for surface-enhanced Raman scattering (SERS). Significant progress has been made on the synthesis of metal nanoparticles with various shapes, composition, and controlled plasmonic properties, all critical for an efficient SERS response. For practical applications, efficient strategies of assembling metal nanoparticles into organized nanostructures are paramount for the fabrication of reproducible, stable, and highly active SERS substrates. Recent progress in the synthesis of novel plasmonic nanoparticles, fabrication of highly ordered one-, two-, and three-dimensional SERS substrates, and some applications of corresponding SERS effects are discussed.

Assessing the Effect of Surface Chemistry on Gold Nanorod Uptake, Toxicity, and Gene Expression in Mammalian Cells

Abstract: Through the use of various layer-by-layer polyelectrolyte (PE) coating schemes, such as the common poly(diallyldimethylammonium chloride)-poly(4-styrenesulfonic acid) (PDADMAC-PSS) system, the mammalian cellular uptake of gold nanorods can be tuned from very high to very low by manipulating the surface charge and functional groups of the PEs. The toxicity of these nanorods is also examined. Since the PE coatings are individually toxic, the toxicity of nanorods coated in these PEs is measured and cells are found to be greater than 90% viable in nearly all cases, even at very high concentrations. This viability assay may not be a complete indicator of toxicity, and thus gene-expression analysis is used to examine the molecular changes of cells exposed to PDADMAC-coated nanorods, which enter cells at the highest concentrations. Indicators of cell stress, such as heat-shock proteins, are not significantly up- or down-regulated following nanorod uptake, which suggests that PDADMAC-coated gold nanorods have negligible impact on cell function. Furthermore, a very low number of genes experience any significant change in expression (0.35% of genes examined). These results indicate that gold nanorods are well suited for therapeutic applications, such as thermal cancer therapy, due to their tunable cell uptake and low toxicity.

Design of an Amphiphilic Polymer for Nanoparticle Coating and Functionalization

Abstract: Inorganic colloidal nanoparticles, such as quantum dots or Au nanoparticles, have been extensively investigated for two decades in physics as well as in chemistry. Applications in a variety of fields such as optics, electronics, and biology are envisaged and important proof-of-concept studies have been reported. In particular, with regard to biologically motivated applications, colloidal stability is a key requirement. Apart from nanoparticles stabilized with small ligand molecules, lipids, [6–8] and surface silanization, amphiphilic polymers have been also used by several groups to disperse originally hydrophobic nanoparticles in aqueous solution. This class of amphiphilic particle coatings not only enables the phase transfer of the nanoparticles from organic solvents to aqueous solution, but also serves as a versatile platform for chemical modification and bioconjugation of the particles because biological molecules can be covalently linked to the polymer surface. Because the stability of the amphiphilic coating around the nanoparticle solely depends on the hydrophobic interaction, this procedure is very general and does, for example, not depend on the material of the inorganic nanoparticle core, as it is the case for ligand exchange protocols. Because of the numerous contact points mediated by hydrophobic interaction, the attachment of the polymer to the particle surface is highly stable and can be improved further by crosslinking of the polymer shell. Nowadays quantum dots coated with amphiphilic polymers and with various biological molecules attached to their surface are commercially available (e.g., Invitrogen). The amphiphilic polymers that have been used so far for coating hydrophobic inorganic nanoparticles consist of hydrophobic side chains for the linkage to the nanoparticle surface and a hydrophilic backbone that provides water solubility through charged groups (in general -COO ) and also acts as an anchor for the attachment of biological molecules with bioconjugate chemistry. In this report, we introduce an amphiphilic polymer which involves a third kind of building block: functional organic molecules. The functional organic molecules are linked to the hydrophobic side chains in a similar way as the hydrophilic backbone and provide additional functionality in the particle surface (Figure 1). The amphiphilic polymer described here is based on a poly(maleic anhydride) backbone. Reaction of a fraction of the anhydride rings with alkylamines leads to the formation of the hydrophobic side chains that are needed for intercalation with the hydrophobic surfactant layer on the nanoparticle surface. Another fraction of the anhydride rings is used to link functional organic molecules to the backbone. Like the alkylamines, organic molecules bearing amino-groups can be directly linked to the anhydride rings by reaction of the anhydride with the amino group. In this way alkylamines and organic molecules with amino terminations can be linked to the polymer backbone in a one-pot reaction. The resulting amphiphilic polymer is then wrapped around hydrophobic capped nanoparticles and the organic solvent is replaced by aqueous solution according to our previously published procedure. By linking some of the remaining anhydride rings with diamine linkers, the polymer molecules around each nanoparticle are interconnected and, thus, the shell is crosslinked. Upon phase transfer to aqueous solution, the remaining anhydride rings open to yield negatively charged carboxyl groups, which provide electrostatic repulsion resulting in a stable dispersion of the nanoparticles. Apart from negatively charged carboxyl groups, the polymer surface of the nanoparticles also contains embedded functional organic molecules. The strategy reported here has several advantageous features: 1) The maleic anhydride moieties react spontaneously with high yield with both amino-modified hydrophobic side-chains (such as alkylamines) and functional organic molecules with amino terminal groups. 2) No additional reagents are needed for the coupling. In comparison, [*] R. A. Sperling, M. Zanella, Prof. W. J. Parak Fachbereich Physik, Philipps Universit#t Marburg Renthof 7, 35037 Marburg (Germany) E-mail: Wolfgang.Parak@physik.uni-marburg.de C.-A. J. Lin, R. A. Sperling, P.-Y. Li, M. Zanella, Prof. W. J. Parak Center for NanoScience Ludwig-Maximilians-Universit#t M8nchen Munich (Germany) C.-A. J. Lin, T.-Y. Yang, W. H. Chang Department of Biomedical Engineering Chung Yuan Christian University Taiwan (ROC) C.-A. J. Lin, J. K. Li, W. H. Chang R&D Center for Membrane Technology Center for Nano Bioengineering Chung Yuan Christian University Taiwan (ROC) [] These authors contributed equally to this work. [] Present address: Institute of Biotechnology, National Cheng Kung University, Taiwan (ROC)

Gecko-inspired directional and controllable adhesion

Abstract: The structure that allows gecko lizards and insects to climb vertical and inverted surfaces with ease has been studied extensively since the mechanism of attachment was shown to be due dominantly to intermolecular surfaces forces. Gecko toes have been shown to adhere with high interfacial shear strength to smooth surfaces (88–200 kPa) using microscale angled fiber structures on their feet. These structures exploit the weak van der Waals interaction forces at the tips of the branching keratinous fiber arrays through their conformation into intimate contact with climbing surfaces, creating a large overall adhesion through millions of sub-micrometer scale contact points. These many contacts also resist peeling by disrupting crack propagations at the interface. Since these discoveries, many attempts have been made to replicate the structures seen in animals using synthetic materials to create adhesives with similar adhesive characteristics. Applications for such adhesives include wall-climbing robots, tissue adhesives for medical applications, and grippers for manipulation. Autumn et al. molded the first synthetic mimics by creating templates using an sharp probe followed by nanomolding. This effort was followed by attempts using electron-beam lithography, carbon nanotubes, nanodrawing, and micro/nanomolding to form high aspect ratio fibrillar structures. Higher adhesion was seen in structures with wider flat mushroom tips, demonstrating that tip size is an important parameter for generating large forces. The wider flat tips increase the contact area and may eliminate the stress singularities along the edge of the interface, as described by Bogy. Adhesion strengths as high as 180 kPa have been demonstrated with vertically aligned mushroom tipped microfibers, although damage occurs to the structures during detachment. Fibrillar structures have also been fabricated to increase (or decrease) friction. In addition, fiber surfaces have been created that provide shear adhesion using vertical arrays of single and multi-walled carbon nanotubes. Unfortunately, these fibrillar structures require very high preloads in order to provide interfacial shear strength. Stiff polypropylene sub-micrometer diameter fibers have been shown to exhibit shear adhesion without requiring high preloading.

Light‐Activated Nanoimpeller‐Controlled Drug Release in Cancer Cells

Abstract: Nanomechanical systems that are designed to trap and release molecules from pores in response to a stimulus are currently the subject of intense investigation.[1–23] Such systems have potential applications for precise drug delivery. A photo-activated material, for example, could release a drug under external control at a specific time and location for phototherapy. Nanomaterials suitable for this type of operation must consist of both an appropriate container and a photoactivated moving component.

Nanostructured copper interfaces for enhanced boiling.

Abstract: Phase change through boiling is used in a variety of heat-transfer and chemical reaction applications. The state of the art in nucleate boiling has focused on increasing the density of bubble nucleation using porous structures and microchannels with characteristic sizes of tens of micrometers. Traditionally, it is thought that nanoscale surfaces will not improve boiling heat transfer, since the bubble nucleation process is not expected to be enhanced by such small cavities. In the experiments reported here, we observed unexpected enhancements in boiling performance for a nanostructured copper (Cu) surface formed by the deposition of Cu nanorods on a Cu substrate. Moreover, we observed striking differences in the dynamics of bubble nucleation and release from the Cu nanorods, including smaller bubble diameters, higher bubble release frequencies, and an approximately 30-fold increase in the density of active bubble nucleation sites. It appears that the ability of the Cu surface with nanorods to generate stable nucleation of bubbles at low superheated temperatures results from a synergistic coupling effect between the nanoscale gas cavities (or nanobubbles) formed within the nanorod interstices and micrometer-scale defects (voids) that form on the film surface during nanorod deposition. For such a coupled system, the interconnected nanoscale gas cavities stabilize (or feed) bubble nucleation at the microscale defect sites. This is distinct from conventional-scale boiling surfaces, since for the nanostructured surface the bubble nucleation stability is provided by features with orders-of-magnitude smaller scales than the cavity-mouth openings.

Microfluidic synthesis of nanomaterials.

Abstract: An overview of the current information and analyses on the microfluidic synthesis of different types of nanomaterial, including metallic and silica nanoparticles and quantum dots, is presented. Control of particle size, size distribution, and crystal structure of nanomaterials are examined in terms of the special features of microfluidic reactors.

Visual cocaine detection with gold nanoparticles and rationally engineered aptamer structures

Abstract: A novel bioassay strategy is designed to detect small-molecule targets such as cocaine, potassium, and adenosine, based on gold nanoparticles (AuNPs) and engineered DNA aptamers. In this design, an aptamer is engineered to be two pieces of random, coil-like single-stranded DNA, which reassembles into the intact aptamer tertiary structure in the presence of the specific target. AuNPs can effectively differentiate between these two states via their characteristic surface-plasmon resonance-based color change. Using this method, cocaine in the low-micromolar range is selectively detected within minutes. This strategy is also shown to be generic and applicable to the detection of several other small-molecule targets.

One- and Two-Dimensional Diffusion of Metal Atoms in Graphene†

Abstract: In the present work, individual Au or Pt atoms in layersconsisting of one or twographene planes have been monitoredin real time at high temperature by high-resolution TEM. Weobtain information about the location of metal atoms ingrapheneandthediffusionmechanisms.Activationenergiesfordiffusion are obtained in a temperature range close to thetemperature of the technically important metal-assisted CVDprocess.Thematerialwassynthesizedinanarcdischarge

Synthesis of biocompatible dextran-coated nanoceria with pH-dependent antioxidant properties

Abstract: Recent reports indicate that cerium oxide nanoparticles (nanoceria) are potent free-radical scavengers with neuroprotective, radioprotective, and anti-inflammatory properties. Nanoceria also have the unique property of being regenerative or autocatalytic. These results point to the possibility of engineering nanoceria with selective antioxidant properties that promote cell survival under conditions of oxidative stress. However, most of these studies have been done with nanoparticles with poor water solubility or synthesized by procedures involving toxic solvents, therefore hindering their potential clinical use. Herein, we report a facile synthesis of monodisperse, water-soluble, and highly crystalline dextran-coated nanoceria (DNC). The improved water solubility of DNC allowed for studies that show a unique pHdependent antioxidant activity that could have important applications in the design of improved therapeutics and in tailoring its antioxidant properties. Our synthetic procedure involves the alkaline-based precipitation of cerium oxide (Ce2O3:CeO2) from a solution containing cerium salt and dextran. Briefly, an aqueous solution of cerium nitrate and dextran was added to an ammonia solution under continuous stirring. Upon formation of the cerium oxide nanocrystals, molecules of dextran coat the nanoparticles’ surface, preventing further growth and resulting in dextran-coated nanoceria (DNC). The DNC preparation is stable in phosphate-buffered saline (PBS) at concentrations of 40mM or higher for months. DNC demonstrates good water stability even after several heating cycles (70–80 8C) with no sedimentation upon centrifugation at 8000 rpm for 30min. These characteristics make our waterbased synthetic method advantageous over organic-solventbased preparations, which are prone to aggregation when suspended in aqueous media.

Simple Synthesis of Functionalized Superparamagnetic Magnetite/Silica Core/Shell Nanoparticles and their Application as Magnetically Separable High‐Performance Biocatalysts

Abstract: Uniformly sized silica-coated magnetic nanoparticles (magnetite@silica) are synthesized in a simple one-pot process using reverse micelles as nanoreactors. The core diameter of the magnetic nanoparticles is easily controlled by adjusting the w value ([polar solvent]/[surfactant]) in the reverse-micelle solution, and the thickness of the silica shell is easily controlled by varying the amount of tetraethyl orthosilicate added after the synthesis of the magnetite cores. Several grams of monodisperse magnetite@silica nanoparticles can be synthesized without going through any size-selection process. When crosslinked enzyme molecules form clusters on the surfaces of the magnetite@silica nanoparticles, the resulting hybrid composites are magnetically separable, highly active, and stable under harsh shaking conditions for more than 15 days. Conversely, covalently attached enzymes on the surface of the magnetite@silica nanoparticles are deactivated under the same conditions.

Single chain epidermal growth factor receptor antibody conjugated nanoparticles for in vivo tumor targeting and imaging.

Abstract: Epidermal growth factor receptor (EGFR) targeted nanoparticle are developed by conjugating a single-chain anti-EGFR antibody (ScFvEGFR) to surface functionalized quantum dots (QDs) or magnetic iron oxide (IO) nanoparticles. The results show that ScFvEGFR can be successfully conjugated to the nanoparticles, resulting in compact ScFvEGFR nanoparticles that specifically bind to and are internalized by EGFR-expressing cancer cells, thereby producing a fluorescent signal or magnetic resonance imaging (MRI) contrast. In vivo tumor targeting and uptake of the nanoparticles in human cancer cells is demonstrated after systemic delivery of ScFvEGFR-QDs or ScFvEGFR-IO nanoparticles into an orthotopic pancreatic cancer model. Therefore, ScFvEGFR nanoparticles have potential to be used as a molecular-targeted in vivo tumor imaging agent. Efficient internalization of ScFvEGFR nanoparticles into tumor cells after systemic delivery suggests that the EGFR-targeted nanoparticles can also be used for the targeted delivery of therapeutic agents.

In Vivo MRI Detection of Gliomas by Chlorotoxin‐Conjugated Superparamagnetic Nanoprobes

Abstract: Converging advances in the development of nanoparticle-based imaging probes and improved understanding of the molecular biology of brain tumors offer the potential to provide physicians with new tools for the diagnosis and treatment of these deadly diseases. However, the effectiveness of promising nanoparticle technologies is currently limited by insufficient accumulation of these contrast agents within tumors. Here a biocompatible nanoprobe composed of a poly(ethylene glycol) (PEG) coated iron oxide nanoparticle that is capable of specifically targeting glioma tumors via the surface-bound targeting peptide, chlorotoxin (CTX), is presented. The preferential accumulation of the nanoprobe within gliomas and subsequent magnetic resonance imaging (MRI) contrast enhancement are demonstrated in vitro in 9L cells and in vivo in tumors of a xenograft mouse model. TEM imaging reveals that the nanoprobes are internalized into the cytoplasm of 9L cells and histological analysis of selected tissues indicates that there are no acute toxic effects of these nanoprobes. High targeting specificity and benign biological response establish this nanoprobe as a potential platform to aid in the diagnosis and treatment of gliomas and other tumors of neuroectodermal origin.

Enhancement of Radiation Cytotoxicity in Breast‐Cancer Cells by Localized Attachment of Gold Nanoparticles

Abstract: Gold nanoparticles (GNPs) and modified GNPs having two kinds of functional molecules, cysteamine (AET) and thioglucose (Glu), are synthesized. Cell uptake and radiation cytotoxicity enhancement in a breast-cancer cell line (MCF-7) versus a nonmalignant breast-cell line (MCF-10A) are studied. Transmission electron microscopy (TEM) results show that cancer cells take up functional Glu-GNPs significantly more than naked GNPs. The TEM results also indicate that AET-capped GNPs are mostly bound to the MCF-7 cell membrane, while Glu-GNPs enter the cells and are distributed in the cytoplasm. After MCF-7 cell uptake of Glu-GNPs, or binding of AET-GNPs, the in vitro cytotoxicity effects are observed at 24, 48, and 72 hours. The results show that these functional GNPs have little or no toxicity to these cells. To validate the enhanced killing effect on cancer cells, various forms of radiation are applied such as 200 kVp X-rays and gamma-rays, to the cells, both with and without functional GNPs. By comparison with irradiation alone, the results show that GNPs significantly enhance cancer killing.

Doxorubicin‐Loaded Polymeric Micelle Overcomes Multidrug Resistance of Cancer by Double‐Targeting Folate Receptor and Early Endosomal pH

Abstract: An optimized, pH-sensitive mixed-micelle system conjugated with folic acid is prepared in order to challenge multidrug resistance (MDR) in cancers. The micelles are composed of poly(histidine (His)-co-phenylalanine (Phe))-b-poly(ethylene glycol) (PEG) and poly(L-lactic acid) (PLLA)-b-PEG-folate. Core-forming, pH-sensitive hydrophobic blocks of poly(His-co-Phe) of varying composition are synthesized. The pH sensitivity of the micelles is controlled by the copolymer composition and is fine tuned to early endosomal pH by blending PLLA(3K)-b-PEG(2K)-folate in the presence of a basic anticancer drug, doxorubicin (DOX). In vitro tests are conducted against both wild-type (A2780) and DOX-resistant ovarian carcinoma cell lines. A mixed-micelle system composed of poly(His-co-Phe (16 mole%))-b-PEG (80 wt%) and PLLA-b-PEG-folate (20 wt%) is selected to target early endosomal pH. DOX-loaded micelles effectively kill both wild-type sensitive (A2780) and DOX-resistant ovarian MDR cancer-cell lines (A2780/DOX(R)) through an instantaneous high dose of DOX in the cytosol, which results from active internalization, accelerated DOX release triggered by endosomal pH, and an endosomal membrance disruption.

Metallic iron nanoparticles for MRI contrast enhancement and local hyperthermia.

Abstract: Current magnetic-nanoparticle technology is challenging due to the limited magnetic properties of iron oxide nanoparticles (IONPs). Increasing the saturation magnetization of magnetic nanoparticles may permit more effective development of multifunctional agents for simultaneous targeted cell delivery, magnetic resonance imaging (MRI) contrast enhancement, and targeted cancer therapy in the form of local hyperthermia. We describe the synthesis and characterization of novel iron-based nanoparticles (FeNPs) coated with biocompatible bis-carboxyl-terminated poly(ethylene glycol) (cPEG). In comparison to conventional IONPs similar in size (10 nm), FeNPs particles have a much greater magnetization and coercivity based on hysteresis loops from sample magnetometry. Increased magnetization afforded by the FeNPs permits more effective generation of local hyperthermia than IONPs when subjected to an oscillating magnetic field in a safe frequency range. Furthermore, FeNPs have a much stronger shortening effect on T2 relaxation time than IONPs, suggesting that FeNPs may be more effective MRI contrast agents. Next-generation FeNPs with a biocompatible coating may in the future be functionalized with the attachment of peptides specific to cancer cells for imaging and therapy in the form of local hyperthermia.

pH-Controlled reversible assembly and disassembly of gold nanorods.

Abstract: Gold nanorods exhibit rich surface-plasmon-resonance (SPR)derived properties, which have made discrete nanorods useful for many interesting applications such as optical data storage, submicrometer metallic barcodes, sensing, biological imaging, and controlled gene delivery. Future scientific and technological applications of Au nanorods require the capability to assemble into complex one-, two-, or even three-dimensional (3D) functional architectures. The assembly of Au nanorods also allows for the utilization of their collective properties that result from the coupling of the optical and electronic properties between neighboring individual nanorods. Several approaches have been developed for the assembly of Au nanorods in either end-to-end (EE) or side-by-side (SS) orientations. They include i) assembly through electrostatic interactions, hydrogen bonding, or covalent bonding, ii) antibody/antigen and streptavidin/biotin biorecognitions, iii) use of carbon nanotubes and silica nanofibers as templates, and iv) interactions between functionalized polymers in selective solvents. Au nanorods assembled by these approaches are generally difficult to disassemble. Even though significant progress has beenmade in the organizationof nanomaterials, reversible assembly and disassembly of Au nanorods in either EE or SS orientations has remained a big challenge. So far, reversible aggregation of spherical Au nanoparticles has been demonstrated by functionalizing them with thiol-modified DNA oligomers. Here, we report on a robust strategy for the reversible assembly and disassembly of Au nanorods in both EE and SS fashion. Thiol-containing bifunctional molecules are selectively bound to the end or side surface of individual Au nanorods. The bound molecules induce the assembly of Au nanorods if the pH of the nanorod solution is adjusted within an optimal range. Outside the optimal pH range, Au nanorods are disassembled. This pH-controlled assembly and disassembly is reversible and can be repeated many times. Moreover, the distances between assembled nanorods are estimated to vary from 0.080 to 1.8 nm for different assemblingmolecules and assembly orientations.

Carbon nanotubes with high bone-tissue compatibility and bone-formation acceleration effects.

Abstract: Carbon nanotubes (CNTs) have been used in various fields as composites with other substances or alone to develop highly functional materials. CNTs hold great interest with respect to biomaterials, particularly those to be positioned in contact with bone such as prostheses for arthroplasty, plates or screws for fracture fixation, drug delivery systems, and scaffolding for bone regeneration. Accordingly, bone-tissue compatibility of CNTs and CNT influence on bone formation are important issues, but the effects of CNTs on bone have not been delineated. Here, it is found that multi-walled CNTs adjoining bone induce little local inflammatory reaction, show high bone-tissue compatibility, permit bone repair, become integrated into new bone, and accelerate bone formation stimulated by recombinant human bone morphogenetic protein-2 (rhBMP-2). This study provides an initial investigational basis for CNTs in biomaterials that are used adjacent to bone, including uses to promote bone regeneration. These findings should encourage development of clinical treatment modalities involving CNTs.

Colorimetric Response of Peptide‐Functionalized Gold Nanoparticles to Metal Ions

Abstract: The design of nanostructures with controlled surface chemistry for sensing, catalytic, and electronic applications is an important research challenge. Sensing platforms based on the optical properties of gold nanoparticles in combination with the molecular recognition of ligands, such as alkyl thiols, antibodies, nucleic acids, and proteins, are active areas of research. Detection of targets by functionalized gold particles has been performed by using surface-enhanced raman spectroscopy (SERS), quartz crystal microgravimetry (QCM), surface plasmon resonance (SPR) spectroscopy, electrochemical and potentiometric detection, and colorimetric assays. The gold-nanaoparticle-based colorimetric sensors provide simplicity and excellent detection capability encompassing a variety of targets including metal ions, DNA, bacterial toxins, protein conformations, and enzyme activity. For example, Pb2þ was detected by a color change upon the dispersion of gold nanoparticles functionalized with DNAzyme. Recently, DNA-modified gold nanoparticles were used as a colorimetric sensor in the detection of Hg2þ.[14] The aggregation of the ligand-functionalized gold nanoparticles upon binding its target results in a colorimetric response caused by broadening and shifting of the plasmon resonance peak. This shift in the plasmon resonance frequency is employed in sensing strategies. To date, the majority of the colorimetric gold nanoparticle sensing strategies have used nucleic acids as the sensing element. Here, we demonstrate the potential of peptide-functionalized gold nanoparticles (PFNs) as a colorimetric sensor for metal ions. The PFNs were synthesized in a HEPES buffer using the Flg-A3 peptide (-Asp-Tyr-Lys-Asp-Asp-Asp-Asp-LysPro-Ala-Tyr-Ser-Ser-Gly-Pro-Ala-Pro-Pro-Met-Pro-Pro-Phe-). The synergistic contributions of both the Flg-A3 peptide and HEPES buffer result in the formation of peptidefunctionalized suspension of gold nanoparticles. The overall negative charge of the peptide (pI1⁄4 3.9) prevents aggregation of the particles by repulsive forces. The surface of the gold nanoparticles contains amino acid functional groups that can interact with metal ions. Charged, aromatic, and hydroxyl-

Mesocrystals: a new class of solid materials.

Abstract: Possible types of, and formation mechanisms for, mesocrystals are summarized. Mesocrystals are a new class of solid materials, which can be regarded as assemblies of crystallographically oriented nanocrystals. Mesocrystals have high crystallinity as well as high porosity, making them promising substitutes for single-crystalline and/or porous polycrystalline materials in many applications such as catalysis, sensing, and solar-energy conversion.

Plasmonic Au/Co/Au Nanosandwiches with Enhanced Magneto-optical Activity†

Abstract: Financial support from the Spanish Ministry of Science and Education (NAN2004-09195-C04-01 and MAT2005-05524-C02-01), and UE (NoE-Phoremost) are acknowledged.

Iridium‐Complex‐Functionalized Fe3O4/SiO2 Core/Shell Nanoparticles: A Facile Three‐in‐One System in Magnetic Resonance Imaging, Luminescence Imaging, and Photodynamic Therapy

Abstract: Highly uniform Fe3O4/SiO2 core/shell nanoparticles functionalized by phosphorescent iridium complexes (Ir) have been strategically designed and synthesized. The Fe3O4/SiO2(Ir) nanocomposite demonstrates its versatility in various applications: the magnetic core provides the capability for magnetic resonance imaging and the great enhancement of the spin-orbit coupling in the iridium complex makes it well suited for phosphorescent labeling and simultaneous singlet oxygen generation to induce apoptosis.

Gold Nanorod Probes for the Detection of Multiple Pathogens

Abstract: Foodborne diseases are associated with five majorpathogens,includingE.coliO157:H7(E.coli)andSalmonellaTyphimurium(S.Typhimurium),andthecostsassociatedwithpreventive and curative measures to combat these five majorpathogens is estimated to be at least $6.9 billion annually,according tothe Economic ResearchService(ERS) in2000.