Experimental Verification of Near-Wall Hindered Diffusion Theory for the Brownian Motion of Nanoparticles using Evanescent Wave Microscopy

A total internal reflection fluorescence microscopy technique coupled with three-dimensional tracking of nanoparticles is used to experimentally verify the theory on near-wall hindered Brownian motion [Goldman et al., Chem. Eng. Sci. 22, 637 (1967); Brenner, Chem. Eng. Sci. 16, 242 (1967)] very close to the solid surface (within ~1 µm). The measured mean square displacements (MSDs) in the lateral x-y directions show good agreement with the theory for all tested nanoparticles of radii 50, 100, 250, and 500 nm. However, the measured MSDs in the z direction deviate substantially from the theory particularly for the case of smaller particles of 50 and 100 nm radius. Since the theory considers only the hydrodynamic interaction of moving particles with a stationary solid wall, additionally possible interaction forces like gravitational forces, van der Waals forces, and electro-osmotic forces have been examined to delineate the physical reasons for the discrepancy

Microscale Investigation of Thermo-Fluid Transport in the Transition FIL, Region of an Evaporating Capillary Meniscus Using a Microgravity Environment

In order to enhance the fundamental understanding of thin film evaporation and thereby improve the critical design concept for two-phase heat transfer devices, microscale heat and mass transport is to be investigated for the transition film region using state-of-the-art optical diagnostic techniques. By utilizing a microgravity environment, the length scales of the transition film region can be extended sufficiently, from submicron to micron, to probe and measure the microscale transport fields which are affected by intermolecular forces. Extension of the thin film dimensions under microgravity will be achieved by using a conical evaporator made of a thin silicon substrate under which concentric and individually controlled micro-heaters are vapor-deposited to maintain either a constant surface temperature or a controlled temperature variation. Local heat transfer rates, required to maintain the desired wall temperature boundary condition, will be measured and recorded by the concentric thermoresistance heaters controlled by a Wheatstone bridge circuit, The proposed experiment employs a novel technique to maintain a constant liquid volume and liquid pressure in the capillary region of the evaporating meniscus so as to maintain quasi-stationary conditions during measurements on the transition film region. Alternating use of Fizeau interferometry via white and monochromatic light sources will measure the thin film slope and thickness variation, respectively. Molecular Fluorescence Tracking Velocimetry (MFTV), utilizing caged fluorophores of approximately 10-nm in size as seeding particles, will be used to measure the velocity profiles in the thin film region. An optical sectioning technique using confocal microscopy will allow submicron depthwise resolution for the velocity measurements within the film for thicknesses on the order of a few microns. Digital analysis of the fluorescence image-displacement PDFs, as described in the main proposal, can further enhance the depthwise resolution

SBC2007-176715 OPTO-ELECTRIC BIOSENSOR TO EXAMINE IN VITRO TOXICITY STIMULI TO ENDOTHELIAL CELL MOTILITY AND MORPHOLOGY

ABSTRACT An integrated opto-electric biosensor is developed that uses an optically transparent and electrically conductive indium tin oxide (ITO) thin film coated on a slide glass substrate. This biosensor can simultaneously acquire the micro-impedance response and microscopic images of live cells in vitro under various toxic agent stimuli. The dynamic response of live porcine pulmonary artery endothelial cells (PPAECs) exposed to various doses of cytochalasin D are comprehensively examined by monitoring the micro-impedance characteristics at a specified frequency and DICM images using the opto-electric biosensor. The change in PPAEC morphology and motility caused by cytochalasin D clearly illustrates the dosedependent actin filament disruption where optical images are correlated with the changes in the micro-electric impedance. INTRODUCTION Micro-impedance sensing has a great deal of potential in quantifying cell physiology by monitoring cells cultured on small gold electrodes [1] Micro-impedance measurements however, are a sensitive and complex function of both cell-cell and cell-substrate interactions. Cellsubstrate interactions, for example, are mediated by integrin receptors that are functionally linked to the actin cytoskeleton. Biophysical cellsubstrate measurements have, therefore, been correlated with widely accepted biochemically established assays for cytotoxicity [2]. Although micro-impedance measurements have proven to be a valuable tool in examining the response of a large group of cells to various dose of cytochalasin D [3], this technique alone cannot completely evaluate inter cellular interactions. In order to properly examine cell-cell, and cell-substrate adhesion, visual techniques are required. Differential interference contrast microscopy (DICM) provides an excellent method for examining these interactions. Both electrically conductive and optically transparent ITO bioelectrodes [4] are combined with an integrated dynamic live cell imaging system. This system can therefore acquire optical and electrical measurements simultaneously, allowing the observation of cytochalasin D effects on live endothelial cells. Of specific interest is the morphological changes caused by the disruption of actin filaments in the cytoskeleton. This biosensor is able to electrically and optically monitor the real-time and label free drug effect on PPEACs with high temporal and spatial resolutions. The actual effect of three actin-affecting drugs (Cytochalasin D, Latrunculin A, and Jasplakinolide) on cell motility has been quantitatively investigated using video-microscopy of cancer cells [5]. The complicated phenomena of cell-substrate interactions and/or cellcell interaction also represent attractive indicators for studying cell signaling and tumor cell inhibition. In tumor cells, for example, it is a major challenge to inhibit the spreading from primary tumor sites to particular organs, which most likely create metastases killing approximately 90% of cancer patients. The present paper presents a new study of morphology and motility of PPAECs caused by cytochalasin D, which inhibits actin polymerization, by using opto-electric biosensors allowing simultaneous dynamic optical and electrical measurements. EXPERIMENT A. Microscopy DICM Senso

A new heat propagation velocity prevails over Brownian particle velocities in determining the thermal conductivities of nanofluids

An alternative insight is presented concerning heat propagation velocity scales in predicting the effective thermal conductivities of nanofluids. The widely applied Brownian particle velocities in published literature are often found too slow to describe the relatively higher nanofluid conductivities. In contrast, the present model proposes a faster heat transfer velocity at the same order as the speed of sound, rooted in a modified kinetic principle. In addition, this model accounts for both nanoparticle heat dissipation as well as coagulation effects. This novel model of effective thermal conductivities of nanofluids agrees well with an extended range of experimental data

Improved functionalization of oleic acid-coated iron oxide nanoparticles for biomedical applications

Superparamagnetic iron oxide nanoparticles can providemultiple benefits for biomedical applications in aqueous environments such asmagnetic separation or magnetic resonance imaging. To increase the colloidal stability and allow subsequent reactions, the introduction of hydrophilic functional groups onto the particles’ surface is essential. During this process, the original coating is exchanged by preferably covalently bonded ligands such as trialkoxysilanes. The duration of the silane exchange reaction, which commonly takes more than 24 h, is an important drawback for this approach. In this paper, we present a novel method, which introduces ultrasonication as an energy source to dramatically accelerate this process, resulting in high-quality waterdispersible nanoparticles around 10 nmin size. To prove the generic character, different functional groups were introduced on the surface including polyethylene glycol chains, carboxylic acid, amine, and thiol groups. Their colloidal stability in various aqueous buffer solutions as well as human plasma and serum was investigated to allow implementation in biomedical and sensing applications.status: publishe

Fundamentals of Energy Transport in Nanofluids Annual Report

The research objectives of this project are the development and applications of nanoparticle analyzing techniques to examine their thermal behaviors in suspension, including the thermal conductivity, thermal (Brownian) diffusion, thermophoresis and thermocapillaryphoresis