Marlon Thomas

Human red blood cells (RBCs) are highly studied by researchers and clinicians alike because RBCs play an essential role in medical diagnostics. RBCs are the most abundant component of whole blood. The accurate analysis of blood samples for blood cells is crucial to help diagnose and management of several life-threatening diseases. Current techniques for analyzing blood cell counts are time-consuming and expensive, requiring a highly trained technician. Implementing a portable, label-free method enables analysis at small clinics and remote locations with reduced times of analysis and cost. The development of miniature, handheld shear-horizontal surface acoustic wave (SH-SAW) biosensors capable of accurately counting RBCs in liquid samples will improve medical diagnostics in resource-limited regions of the United States and parts of the world where access to centralized clinical laboratories is limited. A shear-horizontal surface acoustic wave is a horizontally polarized surface acous...

We describe a rational molecular-level design of biocompatible surface coatings and immobilization of biological species onto them to produce biofunctional interfaces. Our method adapted a strategy for coating glass and other silica-type substrates with bioinert layers of polyethylene glycol (PEG). The introduction of alpha, omega-bifunctional polymers into the coatings allowed for covalent attachment of proteins to the PEGylated surfaces. Spectroscopic studies indicate that the surface-bound proteins had their biological activity preserved.

The objective this paper was to demonstrate a simple protocol for rapid screening of Escherichia coli (E. coli) O157:H7 cells from aqueous samples using a series of three antibody arrays in a microfluidic chip (μ-CHIP). The protocol involved fabricating antibody arrays on glass cover slides using adsorptive coatings the μ-chip with streptavidin and then immobilizing biotin-antibodies against E. coli O157:H7. The arrays were patterned using a straight poly dimethyl siloxane (PDMS) channel to create rectangular shaped arrays with the protein streptavidin deposited on the bottom glass surface. Streptavidin served as the anchor for biotin-labeled antibodies to attach, since biotin and streptavidin spontaneously bind to each other due to their receptor ligand interaction. Employing an array of three rectangular surfaces with immunoassays immobilized in the μ-chip, we were able to capture fluorescently labeled E. coli O157:H7 cells from known samples. After immunocapture and enumeration o...

We describe a facile and expedient approach for the fabrication of arrays of microelectrodes on smooth substrates. A sequence of print-and-peel procedures allowed for the microfabrication of capacitance microsensors using office equipment and relatively simple wet chemistry. Microfluidic assemblies with reversibly adhered elastomer components allowed for the transfer of patterns of metallic silver, deposited via Tollens' reaction, onto the substrate surfaces. Electroplating of the silver patterns produced an array of micrometer-thick copper electrodes. Capacitance sensors were assembled by placing nonlithographically fabricated flow chambers over the microelectrode arrays. Triangular-waveform current-voltage (I/V) measurements showed a linear correlation between the capacitance of the print-and-peel fabricated devices and the dielectric constant of the samples injected into their flow chambers.

... Page 13. xi Abstract Towards A Targeted Surfactant Stabilized Ultrasound Contrast Agent Marlon Thomas Margaret A. Wheatley ... the resonance frequency of the microbubble significantly increases the ratio of the scattering cross sections to the physical cross section (Hoff, 1996). ...

For more than a century, colorimetric and fluorescence staining have been the foundation of a broad range of key bioanalytical techniques. The dynamics of such staining processes, however, still remains largely unexplored. We investigated the kinetics of fluorescence staining of two gram-negative and two gram-positive species with 3,3'-diethylthiacyanine (THIA) iodide. An increase in the THIA fluorescence quantum yield, induced by the bacterial dye uptake, was the principal reason for the observed emission enhancement. The fluorescence quantum yield of THIA depended on the media viscosity and not on the media polarity, which suggested that the microenvironment of the dye molecules taken up by the cells was restrictive. The kinetics of fluorescence staining did not manifest a statistically significant dependence neither on the dye concentration, nor on the cell count. In the presence of surfactant additives, however, the fluorescence-enhancement kinetic patterns manifested species specificity with statistically significant discernibility.

Advection driven mixing is essential for microfluidics and poses challenges to the design of microdevices. Force transducers or complex channel configurations provide means for, respectively, active or passive disrupting of laminar flows and for homogenizing the composing fluids. Print-and-peel (PAP) is a nonlithographic fabrication technique that involves direct printing of masters for molding polymer components of microdevices. PAP, hence, allows for facile and expedient preparation of microfluidic devices, without requiring access to specialized microfabrication facilities. We utilized PAP for fabrication of microfluidic devices capable of turning, expanding, and contracting microflows. We examined the mixing capabilities of these devices under flow conditions of small Reynolds numbers (0.2-20) and large Peclet numbers (260-26 000), under which advection is the dominant mode of mass transfer. We focused on mixing channels with arched shapes and examined the dependence of the mixi...