Woo-Jae Kim

Fabricating Genetically Engineered High-Power Lithium Ion Batteries Using Multiple Virus Genes

Viral Battery In developing materials for batteries, there is a trade-off between charge capacity, conductivity, and chemical stability. Nanostructured materials improve the conductivity for some resistive materials, but fabricating stable materials at nanometer-length scales is difficult. Harnessing their knowledge of viruses as toolkits for materials fabrication, Lee et al. (p. 1051; published online 2 April) modified two genes in the filamentous bacteriophage M13 to produce a virus with an affinity for nucleating amorphous iron phosphate along its length and for attaching carbon nanotubes at one of the ends. In nanostructured form, the amorphous iron phosphate produced a useful cathode material, while the carbon nanotubes formed a percolating network that significantly enhanced conductivity. A genetically modified virus is used to form an efficient cathodic battery material. Development of materials that deliver more energy at high rates is important for high-power applications, including portable electronic devices and hybrid electric vehicles. For lithium-ion (Li+) batteries, reducing material dimensions can boost Li+ ion and electron transfer in nanostructured electrodes. By manipulating two genes, we equipped viruses with peptide groups having affinity for single-walled carbon nanotubes (SWNTs) on one end and peptides capable of nucleating amorphous iron phosphate(a-FePO4) fused to the viral major coat protein. The virus clone with the greatest affinity toward SWNTs enabled power performance of a-FePO4 comparable to that of crystalline lithium iron phosphate (c-LiFePO4) and showed excellent capacity retention upon cycling at 1C. This environmentally benign low-temperature biological scaffold could facilitate fabrication of electrodes from materials previously excluded because of extremely low electronic conductivity.

Dynamics of Surfactant-Suspended Single-Walled Carbon Nanotubes in a Centrifugal Field

A hydrodynamic model is used to describe the motion of surfactant-suspended single-walled carbon nanotubes in a density gradient, while being subjected to a centrifugal field. The number of surfactant molecules adsorbed on each nanotube determines its effective density and, hence, its position in the gradient after centrifugation has been completed. Analysis of the spatial concentration distributions of CoMoCAT nanotubes suspended with 2 w/v% sodium cholate yielded 2.09, 2.14, and 2.08 surfactant molecules adsorbed per nanometer along the length of the (6,5), (7,5), and (8,7) nanotubes, respectively. The estimates are commensurate with experimental values reported in the literature and can be used to predict the fate of sodium cholate-suspended nanotubes in the separation process. Since the density of the surfactant-nanotube assembly is highly sensitive to the number of adsorbed molecules, a perturbation would cause it to be enriched at a different location in the gradient. The level of sensitivity is also reflected in the 95% confidence levels that are reported in this work.

Exciton antennas and concentrators from core-shell and corrugated carbon nanotube filaments of homogeneous composition.

There has been renewed interest in solar concentrators and optical antennas for improvements in photovoltaic energy harvesting and new optoelectronic devices. In this work, we dielectrophoretically assemble single-walled carbon nanotubes (SWNTs) of homogeneous composition into aligned filaments that can exchange excitation energy, concentrating it to the centre of core-shell structures with radial gradients in the optical bandgap. We find an unusually sharp, reversible decay in photoemission that occurs as such filaments are cycled from ambient temperature to only 357 K, attributed to the strongly temperature-dependent second-order Auger process. Core-shell structures consisting of annular shells of mostly (6,5) SWNTs (E(g)=1.21 eV) and cores with bandgaps smaller than those of the shell (E(g)=1.17 eV (7,5)-0.98 eV (8,7)) demonstrate the concentration concept: broadband absorption in the ultraviolet-near-infrared wavelength regime provides quasi-singular photoemission at the (8,7) SWNTs. This approach demonstrates the potential of specifically designed collections of nanotubes to manipulate and concentrate excitons in unique ways.

Connecting Single Molecule Electrical Measurements to Ensemble Spectroscopic Properties for Quantification of Single-Walled Carbon Nanotube Separation

We directly compared ensemble spectroscopic measurements to a statistically rigorous single molecule electrical characterization of individual SWNT devices using a high throughput electrical probe station and reported, for the first time, a highly accurate extinction coefficient ratio for metallic to semiconducting SWNTs of 0.352 +/- 0.009. The systematic counting of metallic and semiconducting types from solution also allows us to examine the variances associated with device properties and therefore provide the first measure of potential defect generation during processing methods.

Highly efficient exfoliation of individual single-walled carbon nanotubes by biocompatible phenoxylated dextran

Highly efficient exfoliation of individual single-walled carbon nanotubes (SWNTs) was successfully demonstrated by utilizing biocompatible phenoxylated dextran, a kind of polysaccharide, as a SWNT dispersion agent. Phenoxylated dextran shows greater ability in producing individual SWNTs from raw materials than any other dispersing agent, including anionic surfactants and another polysaccharide. Furthermore, with this novel polymer, SWNT bundles or impurities present in raw materials are removed under much milder processing conditions compared to those of ultra-centrifugation procedures. There exists an optimal composition of phenoxy groups (∼13.6 wt%) that leads to the production of high-quality SWNT suspensions, as confirmed by UV-vis-nIR absorption and nIR fluorescence spectroscopy. Furthermore, phenoxylated dextran strongly adsorbs onto SWNTs, enabling SWNT fluorescence even in solid-state films in which metallic SWNTs co-exist. By bypassing ultra-centrifugation, this low-energy dispersion scheme can potentially be scaled up to industrial production levels.

Water-stable single-walled carbon nanotubes coated by pyrenyl polyethylene glycol for fluorescence imaging and photothermal therapy

Nanomaterials have recently received significant attention as photothermal agents and fluorescence contrast agents for molecular therapeutics due to their unique optical properties (e.g. light absorption). In particular, single-walled carbon nanotubes (SWNTs) have been recently utilized as photothermal agents (for photothermal therapy) because of the solubility of SWNTs as well as their light absorbing capability at the near-infrared region. In this work, we have developed the SWNT-based photothermal agents using pyrene-based PEGylation of SWNTs. FT-IR and/or H-NMR spectroscopies have validated the PEGylation of SWNTs, and it is shown that water-soluble SWNTs are able to generate heat under near-infrared (NIR) irradiation of 5W/cm2. Moreover, it is found that our pyrene-based PEGylated SWNTs exhibit the fluorescence characteristic under the excitation wavelength of 340 nm. Our study sheds light on the pyrenyl PEGylated SWNTs as photothermal agents and/or fluorescence contrast agents for the future applications in molecular therapeutics.

Highly Selective Photothermal Therapy by a Phenoxylated‐Dextran‐Functionalized Smart Carbon Nanotube Platform

Near-infrared (NIR) photothermal therapy using biocompatible single-walled carbon nanotubes (SWNTs) is advantageous because as-produced SWNTs, without additional size control, both efficiently absorb NIR light and demonstrate high photothermal conversion efficiency. In addition, covalent attachment of receptor molecules to SWNTs can be used to specifically target infected cells. However, this technique interrupts SWNT optical properties and inevitably lowers photothermal conversion efficiency and thus remains major hurdle for SWNT applications. This paper presents a smart-targeting photothermal therapy platform for inflammatory disease using newly developed phenoxylated-dextran-functionalized SWNTs. Phenoxylated dextran is biocompatible and efficiently suspends SWNTs by noncovalent π-π stacking, thereby minimizing SWNT bundle formations and maintaining original SWNT optical properties. Furthermore, it selectively targets inflammatory macrophages by scavenger-receptor binding without any additional receptor molecules; therefore, its preparation is a simple one-step process. Herein, it is experimentally demonstrated that phenoxylated dextran-SWNTs (pD-SWNTs) are also biocompatible, selectively penetrate inflammatory macrophages over normal cells, and exhibit high photothermal conversion efficiency. Consequently, NIR laser-triggered macrophage treatment can be achieved with high accuracy by pD-SWNT without damaging receptor-free cells. These smart targeting materials can be a novel photothermal agent candidate for inflammatory disease.