Bioinspired Antidew Superhydrophobicity

Many plants exhibit remarkable water repellency owing to their rough surface. The textured surface traps air underneath water drops and the air cushioning gives rise to the superhydrophobicity. However, biomimetic superhydrophobic surfaces generally do not retain water repellency when exposed to a condensing environment. Water condensate proceeding from nanoscale nuclei tends to penetrate into the surface texture and displace the trapped air, forfeiting the superhydrophobicity.  

In this talk, we will show that lotus leaves use two complementary strategies to achieve antidew superhydrophobicity. For condensate drops that are order of 100 um or smaller, drop coalescence triggers a self-propelled jumping motion which removes the sticky condensate along the pathway [PRL, 103, 174502]. For drops that are order of 1 mm or larger, lotus leaves harvest energy from ambient vibrations to overcome the adhesion between the sticky condensate and the rough surface [PRL, 103, 184501].

Probing Complex Systems with One and Two-Dimensional Distribution Functions of Diffusion and Relaxation

Many systems of interest in biology or geology are intrinsically complex and are difficult to characterize with standard experimental techniques. In this talk, I will discuss a recently introduced NMR based technique to determine one- and two-dimensional distribution functions of diffusion and relaxation. It is shown that such measurements are well suited to study fluids in heterogeneous porous media. Since the diffusion and relaxation rates of the fluid molecules in such systems are controlled by the local geometry of the pore space, diffusion-relaxation distribution functions give information about the spatial configuration and connectivity of each fluid phase. In complex fluids, diffusion – relaxation distribution functions are related to the correlations of the translational and rotational diffusion coefficients and can be used to infer the distribution of molecular size in the fluid. In colloidal systems, these measurements enable the determination of the aggregate size and of the interactions between the aggregates and the different fluid components. Unlike conventional NMR experiments, these techniques can be performed in inhomogeneous magnetic fields and have already found wide spread application in commercial NMR logging of oil wells.

(This research is supported by grants from the National Cancer Institute, National Institute of Biomedical Imaging and Bioengineering, UNC Lineberger Cancer Center, University Cancer Research Fund, and Xintek)

Purpose: Nitric oxide (NO) is a key player in modulating vascular tone, angiogenesis, vascular permeability, platelet aggregation and adhesion, and leukocyte adhesion. The maintenance of sufficient NO bioavailability in the presence of vast quantities of scavenging molecules such as hemoglobin and myoglobin is accomplished largely by compartmentalization, for example of hemoglobin in red cells. Disruption of NO bioavailability due to hemolysis or other factors contributes to pathology in a variety of disease and conditions including sickle cell disease, arteriosclerosis, cancer, diabetes, and others. The Kim-Shapiro lab aims to elucidate basic physiological mechanisms that preserve NO bioavailability, how these are disturbed in various diseases, and how these can be preserved through therapeutics. Methods: A variety of biochemical and biophysical tools are used to measure and/or calculate NO or other nitrogen oxide concentrations under a variety of conditions. These include electron paramagnetic resonance spectroscopy (where NO products can be quantified at submicromolar concentrations in whole blood), chemiluminescence detection (where NO can be quantified at nanomolar quantities), stopped-flow and laser pump probe absorption spectroscopy, laser diffraction red cell deformability imaging, and computational finite element simulations. Results: The Kim-Shapiro lab has discovered that reduced NO scavenging by hemoglobin in normal physiology is mainly due rate-limitations for NO to diffuse to the red cell but that red cell membrane permeability also plays a role and this is modulated by oxygen tension [1]. When hemolysis occurs, as little as one micromolar intravascular hemoglobin can drastically reduce NO bioavailability even in the presence of ten millimolar red cell encapsulated hemoglobin that is usually present [2]. NO bioavailability may be restored using nitrite therapy. Contrary to the previously held belief that nitrite is biologically inert, the Kim-Shapiro lab (in collaboration with the Gladwin lab) discovered that nitrite is a vasodilator and may serve as a storage pool for nitric oxide that is activated by deoxygenated hemoglobin under hypoxic conditions [3]. This activation involves a new nitrite reductase/anhydrase activity of hemoglobin [4]. Current therapeutic interventions being explored include oral nitrate. Conclusions: NO bioavilability is reduced in a variety of diseases and can be restored by nitrite therapy or other therapies the Kim-Shapiro lab is exploring. A host of animal and human studies for cerebral vasospasm, ischemic reperfusion injury, pulmonary hypertension and others have been completed and are ongoing. Supported by the NIH.

[1] Azarov, I.; Huang, K. T.; Basu, S.; Gladwin, M. T.; Hogg, N.; Kim-Shapiro, D. B. Nitric oxide scavenging by red blood cells as a function of hematocrit and oxygenation, J. Biol. Chem., 280:39024-38032; 2005.

[2] Jeffers, A.; Gladwin, M. T.; Kim-Shapiro, D. B. Computation of plasma hemoglobin nitric oxide scavenging in hemolytic anemias, Free Radic. Biol. Med., 41:1557-1565; 2006.

[3] Cosby, K.; Partovi, K. S.; Crawford, J. H.; Patel, R. P.; Reiter, C. D.; Martyr, S.; Yang, B. K.; Waclawiw, M. A.; Zalos, G.; Xu, X. L.; Huang, K. T.; Shields, H.; Kim-Shapiro, D. B.; Schechter, A. N.; Cannon, R. O.; Gladwin, M. T. Nitrite reduction to nitric oxide by deoxyhemoglobin vasodilates the human circulation, Nat. Med., 9:1498-1505; 2003.

[4] Basu, S.; Grubina, R.; Huang, J.; Conradie, J.; Huang, Z.; Jeffers, A.; Jiang, A.; He, X.; Azarov, I.; Seibert, R.; Mehta, A.; Patel, R.; King, S. B.; Hogg, N.; Ghosh, A.; Gladwin, M. T.; Kim-Shapiro., D. B. Catalytic generation of N2O3 by a concerted nitrite reductase and anhydrase activity of hemoglobin, Nature Chemical Biology, 3:785-794; 2007.

We will then describe progress in a number of ongoing projects that are based on the basic idea of nanofluidic manipulation of DNA. In particular, we have begun to develop a toolbox for connecting nanochannels into networks, and control the motion of single molecules by creating a spatially and temporally modulated energy landscape. In context we also discovered that polyelectrolytes in good solvents can be both stretched and contracted in a.c. electric fields if certain conditions are met. We further studies the fluctuation spectrum of nanoconfined polymers. The second branch of our current research is the application of nanofluidic confinement to biological problems. In particular we will describe progress in reading the epigenetic code of chromatin, and work towards electric sequencing of DNA.DNA stretching in nanofluidic channels that are round 100 nm in diameter and 100's of microns long is an emerging technique for the genetic analysis of long nucleic acid molecules. We will explain why nanofluidic stretching differs from other single-molecule techniques, in particular how the ability to measure individuality is greatly enhanced by the fundamentally different averaging properties. We will present an overview of the basic physics that enables this exciting new technique, and discuss proof-of-principle experiments that have demonstrated how genetic information can be gathered by the technique.

We measure tunneling through a single quantum level in a carbon nanotube quantum dot connected to resistive metal leads. For the electrons tunneling to/from the nanotube, the leads serve as a dissipative environment, which suppresses the tunneling rate. In the regime of sequential tunneling, the height of the single-electron conductance peaks increases as the temperature is lowered, although it scales more weakly than the conventional ~1/T. In the resonant tunneling regime (temperature smaller than the level width), the peak width approaches saturation, while the peak height starts to _decrease_. Overall, the peak height shows a non-monotonic temperature dependence. We associate this unusual behavior with the transition from the sequential to the resonant tunneling through a single quantum level in a dissipative environment. We draw a connection between our results and the recent theories on a quantum dot with Luttinger liquid leads.Given sufficient time, I will briefly describe our very recent results on the 'Kondo box' in a carbon nanotube.

Optical coherence tomography: From biomedical imaging to basic science

Ph.D. Prelim Exam

Hydrogen Storage and Beyond: NMR Techniques for Characterizing Surfaces and Pores

Magnetic and metallic ligand-stabilized nanoparticles: Chemical and nanostructural transformations and self-assembly into monolayers

Nanostructural transformations of metal NPs driven by chemical reactions, such as the nanoscale Kirkendall effect, are useful for synthesizing complex nanostructures and for controlling their properties. Three studies of NP transformations will be presented: (1) When Ni nanoparticles of different sizes are oxidized to NiO through the nanoscale Kirkendall effect, the resulting nanostructures strongly depend on the NP size. (2) In the synthesis of nickel phosphide NPs, the P:Ni molar ratio of the reactants determines whether the nanoparticles have crystalline-hollow, crystalline-solid, or amorphous-solid nanostructures. (3) Addition of Ag+ to Au NPs during digestive ripening results in Au(core)/Ag(shell) NPs that convert to AuAg alloy NPs upon annealing.

Spin casting is an attractive method for assembling NP monolayers, because it is fast and economical. The formation of monolayers of ligand-stabilized NPs with diameters below 10 nm through spin casting onto SiN membranes will be discussed. SiN membranes facilitate detailed high-resolution characterization of spin-cast arrays of spherical FePt and Ni NPs by transmission electron microscopy. Monolayer regions upwards of 10 μm2 were achieved, while single hexagonal close-packed (HCP) grains as large as 0.5μm2 were observed but contained both line and point defects. Edge dislocations, interstitials, vacancies, and overlapping particles were observed. Grain analysis of the monolayer arrays elucidates their structure, including boundaries, orientation, defects, and correlation lengths. Deviations from HCP ordering occur as the normalized standard deviation of the sample’s size distribution increases.

Quantitative Characterization of Physico-Chemical Properties of the Active Layers of Reverse Osmosis and Nanofiltration Membranes, and Their Relation to Membrane Performance

Department of Environmental Sciences and Engineering, UNC-Chapel Hill