Physics and Astronomy At The University of Georgia

Recently carbon nanotube (CNT) membrane has been a subject of intensive research activities due to their unique attributes, such as i) a dramatically enhanced fluid flow, ii) functional chemistry at the CNT tip entrance for effective chemical and biological separations, and iii) electrically conductive carbon nanotubes allowing for efficient electrochemical functionalization and electro-osmosis pumping.1-5 Meanwhile, the estimated overall costs of drug addiction and abuse in the United States alone exceed half a trillion dollars annually as reported by National Institute on Drug Abuse (NIDA). Classical transdermal patches for drug addiction and abuse treatments like nicotine patch can only provide constant dosing rates. However many drug abuse and addiction treatments demands variable dosing rates. Herein, a relatively low-cost microtoming method has been developed to fabricate carbon nanotube (CNT) membranes in large scale. The tips of CNT membranes were functionalized using an efficient electrochemical grafting method, following by a series of chemical coupling reactions. It was demonstrated that Ionic mobilities through CNT cores are enhanced by a factor of ~4 with a significant rectification seen for large anion/cation mixtures. High electro-osmotic flows of ~3 cm/s-V is seen for ~ 1nm single walled CNTs and ~0.15 cm/s-V for ~ 7nm multi-walled CNTs. The enhanced electrophoretic and electro-osmotic phenomenon of CNT membranes have been successfully applied to a programmed transdermal nicotine patch that can provide therapeutically useful fluxes ranging from high (1.30.65 μmol/hr-cm2) and to low (0.330.22 μmol/hr-cm2) for efficient smoking cessation treatments (in vitro (human skin) & in vivo (hairless guinea pig)).

Bio: Dr. Ji Wu is an assistant professor of chemistry at Georgia Southern University, Statesboro, GA. He has been working as a postdoctoral scholar in University of Kentucky with research focus on the fabrication, electro-kinetics and applications of carbon nanotube membranes from 2007-2012. He received his PhD degree in Inorganic and Materials Chemistry from Texas Christian University in 2007, following his Advisor, J. L. Coffer. His PhD research was on erbium-doped semiconducting nanomaterials such as silicon and germanium nanowires. He also earned a Masters’ degree in Organometallic Chemistry from Anhui University (Hefei, China) in 2000. He has contributed over 20 publications on peer-reviewed journals, such as Nature Nano., PNAS, Nano Letters, Advanced Materials, J. Pharm. Sci. etc.

When metal nanoparticles are excited by light resonant with the particle’s surface plasmon, non-radiative relaxation efficiently generates heat in the immediate region surrounding the particle. Such photothermal heating has been extensively explored in solution environments for applications such as cancer treatment and drug delivery. In contrast, use of and understanding of photothermal heating in solids, such as nanoparticle-polymer composites, has been limited. However, such photothermal effects could facilitate in situ thermal processing of polymeric materials via externally-controllable light excitation. The spatial specificity and temperatures achieved can potentially be used for triggering phase transitions, cross-linking, or driving region-specific chemical reactions inside the existing material. Anisotropic particles enable further tuning of the plasmonic frequency and polarization-controlled heating. By embedding fluorophores in the composite, a sensitive relative fluorescence approach can be utilized to dynamically monitor the average temperature within the sample as it is thermally processed. With modest light intensities and dilute nanoparticle concentrations, controllable temperature changes of several hundred degrees Celsius have been achieved.

Paramyxovirus family includes many important human and animal pathogens. Virus is a parasite of host cells: it requires host cellular proteins for survival and efficient replication. Our work focuses on investigating the interface of virus and host cells. We have identified host kinases that are important for virus replication. We have been exploring targeting host kinases as novel anti-viral therapies. Understanding virus and host cell interactions is also important for developing effective vaccines, a proven method for preventing viral infections. We have taken advantages of knowledge generated from our basic research to develop novel therapies for virus infection as well as for cancer.

Discovery of protein drugs has been one of the major focuses in biotechnology. Conventional approach involves expression of the candidate protein in cultured cells, isolation of the expressed protein from cell extracts or medium, and assessment of its therapeutic activity by injecting the protein into an animal. This talk will describe a new approach toward identification of a therapeutic protein or for protein drug discovery. The strategy involves the development of gene delivery method to allow expression of the candidate gene directly in animals bearing a disease, thereby bypassing the need for preparation and administration of protein into animals. The talk will center around recent progress in development of synthetic carriers and physical method for gene delivery. The advantage and disadvantages of the delivery
systems, and their potential for gene therapy will also be discussed.

In this presentation, I will discuss about how the first-principles computational methods (quantum mechanics and molecular dynamics simulation) can make contributions to the nanobio technology: understanding of the given nanoscale systems and design of new systems. The first part is the nanostructured polymer membranes for fuel cell technology in which the first-principles methods were used to establish understandings of the relationship between the nanostructures of material and the proton transport properties. First, the hydrated nafion membrane is discussed for the structure-property relationship, and then a new molecular architecture designed from such relationship is presented. In the second part of this presentation, I will talk about the nanoscale molecular electronics such as molecular switch showing an electromechanical switching behavior. In this part, the first-principles methods predict the probable molecular configurations of molecular electronic device and its corresponding electron transport properties. For the last part of my talk, I will present the nanostructured biomaterials such as hydrogel in which a hydrophilic polymer network confines significant amount of water. To develop a good hydrogel with desirable properties in terms of mechanical and transport properties, the molecular mechanisms for mechanical deformation and molecular diffusion are investigated using the first-principles.The bottom line of my talk is how the multiscale first-principles computational methods can work together to investigate the nanoscale systems and help design new material based on the structure-property relationship for better desirable properties.

Understanding and mapping the organizational architecture of the brain has been of keen interest for centuries. With the advancements of modern imaging techniques, the pace of scientific discoveries of principles underlying the evolution, development, and organization of brain architectures has been accelerated. This talk will present our recent efforts in discovering general principles of structural, connectional and functional brain architectures by applying macro-scale neuroimaging and micro-scale bioimaging techniques and computational methods. The applications of these discovered principles in neuroscience, medicine and computer science will also be showcased and discussed.

Thermoelectric (TE) energy conversion is a technology that converts thermal energy to electrical power and vice versa. Thermoelectric technology has significant advantages over other energy conversion technologies due to its compactness, high reliability and zero emissions of noise and pollutants. However, the energy conversion efficiency in existing thermoelectric devices is typically low. Since early 1990s, many studies have shown that higher energy conversion efficiency is achievable by reducing the phonon
thermal conductivity of TE materials using nanostructured thermoelectric materials. While the future of the technology is promising, the performance of state-of-the-art nanostructured materials is still much less than that of the conventional energy conversion techniques. In this work, we suggest that, by utilizing the different responses of electron and phonon transport to mechanical strains, the efficiency of
nanocomposite TE materials can be further improved through mechanical tuning. We perform computational analysis to investigate strain effect on the thermoelectric figure of merit in n-type Ge nanowire-Si host nanocomposite materials. The Seebeck coefficient and electrical conductivity of the Si/Ge nanocomposites are calculated by an analytical model derived from the Boltzmann transport equation (BTE) under the relaxation-time approximation. The effect of strain is incorporated into the BTE through strain induced energy shift and effective mass variation calculated from the deformation potential theory and a degenerate kp method. Strain effect on phonon thermal conductivity in the nanocomposites is computed through a model combining the strain dependent lattice dynamics and the ballistic phonon BTE. Electronic thermal conductivity is computed from electrical conductivity by using the Wiedemann-
Franz law. Normal and shear strains are applied in the transverse plane of the Si/Ge nanocomposites. Thermoelectric properties including electrical conductivity, thermal conductivity, Seebeck coefficient and dimensionless figure of merit are computed for Si/Ge nanocomposites under these strain conditions.

Dielectrophoresis (DEP) is a powerful tool that has been widely used to manipulate (e.g., focus, trap, concentrate, and sort) particles and cells in microfluidic devices. Traditional electrode-based DEP (eDEP) arises from the non-uniform high-frequency AC electric field between pairs of electrodes that are fabricated within a microchannel. This method suffers from the problems of fabrication complexity and electrode fouling etc. Such problems are significantly mitigated in the so-called insulator-based DEP (iDEP) devices, where both AC and DC electric fields can be applied through the electrodes that are positioned virtually outside a microchannel. However, in-channel insulating obstacles such as hurdles, posts, and ridges are required to create the electric field gradients. The locally amplified electric field around these micro-obstacles may cause adverse effects on both the sample and the device due to potential Joule heating and particle clogging issues. Our group has recently developed a new method that exploits the curvature of insulating walls for a diverse electrical control of particle and cell motions in microfluidic devices. Due to the variation in path length for electric current, the electric field becomes inherently non-uniform within a microchannel corner. Thus induced DEP can generate both a crossstream and a counter-stream particle motion, which are second-order function of the electric field and are superimposed to the linear electrokinetic motion for flexible particle manipulations. In this talk I will present our recent results on the dielectrophoretic focusing, trapping, concentration, and separation of particles and cells in curved microchannels and microfluidic reservoirs with applications to lab-on-a-chip systems.

Our group has taken advantage of the ease of functionalizing norbornene monomers to make a range of polynorbornenes with designed activities. In our bio-project, one set of water-soluble polymers has been shown to interact with bacterial membranes in several distinct ways including disruption and penetration. We have measured the interactions of three of them with E. coli lipid extract vesicles using a Biacore SPR biosensor. These preliminary binding studies results will be presented. Our materials project involves a set of polymers with promising fire-retardant properties. We have observed how they perform on their own and also as additives in treated paper and polyurethane films. Most recently we have attempted to use our polymers to surface modify magnesium hydroxide which itself is a flame-resistant additive, but only at high loadings. Both of these projects have demonstrated that tuning the properties, of membrane-active agents and fire-retardant additives, can be achieved through facile modifications of the polymer along the
backbone and side chains.

The presentation will briefly discuss our multidentate approach to create uniform metal nanoparticles by tailoring the core-ligand interactions. Exciting electrochemical and optical activities from sub-2-nm Au nanoparticles are reported. The talk will focus on novel mass transport behaviors through a single nanosized pipette or pore, analyzed by time and frequency domain electrochemical measurements and classic simulation. As the pore dimension miniaturizes and approaches that of a single bio-macromolecule, single molecule activities inside the mass transport limiting region perturb the ionic transport current thus be detected. Correlated with the well-known ion current rectification effect observed from various nanodevices, multitime-constant transport processes have been discovered. The knowledge allows us to differentiate the respective contribution to the current signal from substrate charges (coulomb interaction with fixed surface charges) and nanogeometry (volume effect). The transference number of cation and anion, and surface charge density of individual nanodevices, have been determined by combined experiments and simulation.