We are broadly interested in the interaction between complex fluids (polymers, colloids, nanoparticles, bacteria, protozoa, cells) and the surfaces that confine or support them. These interactions appear ubiquitously in applications in petroleum engineering (drilling media, microbial corrosion), environmental engineering (biofouling, bioremediation), materials engineering (rapid prototyping, direct-write assembly), and biodefense (diagnostics, biodetection).  Moreover, this broad class of problems is scientifically fascinating: both the chemical and mechanical properties of surfaces can influence the adhesion, diffusion, motility, and phase behavior of complex fluids. Our current research thrusts include:

Flow and Transport of Complex Fluids in Confinement

Processes involving the flow of complex fluids in confined geometries appear prominently in technological, environmental, and physiological settings. Confinement effects strongly influence multiphase transport properties, and are thus relevant for technological applications involving porous media, such as gel electrophoresis and chromatography, and critical resource applications, such as water remediation and oil extraction from nonconventional sources. Despite their ubiquity, the science underlying these processes remains poorly understood. We use confocal and light microscopy to directly image the flow of complex fluids in microchannels. By quantifying the flow behavior in a variety of controlled microscale geometries using high-throughput tracking algorithms, we will identify the effects of confinement on the flow properties of complex fluids and inspire new designs for manipulating these materials on the microscale. Currently, we are investigating the effects of confinement on the structure, dynamics, and phase behavior of quiescent and flowing model colloid-polymer mixtures (in part with Jeremy Palmer), and the transport properties of nanoparticles in microfabricated post arrays and polymer solutions (with Ramanan Krishnamoorti).

Near-Surface Motility of Microorganisms

Over 99% of bacteria live in bacterial biofilms, which are surface-associated communities surrounded by a protective extracellular matrix that increases the resistance of bacteria to environmental and host stresses. These stress-resistant biofilms thus cause significant problems both in human health and in industrial processes. Preventing their formation requires understanding how bacteria adapt their motility mechanisms near surfaces. We directly image the motion of bacteria and other microorganisms near engineered surfaces with confocal and light microscopy. By translating microscopy images into a searchable database of trajectories, we will elucidate the effects of surface properties on microbial motility and inspire new strategies to create antifouling materials.  Currently, we are quantifying the near-surface motility mechanisms of model bacteria on engineered surfaces, and applying insights gained from these studies to understand how bacteria respond to self-cleaning surfaces (with Megan Robertson) and identifying appendage-driven attachment mechanisms (in part with Patrick Cirino).

Biomedical Applications: Lateral Flow Assays and Protein Crystallization

We apply the fundamental scientific principles identified in other studies to address critical needs in public health. With Richard Willson, we are applying our insights into nanoparticle transport in porous media to design sensitive, specific, inexpensive, and portable diagnostics based on lateral flow immunoassays (the format used in the common pregnancy test). Our assays employ engineered viral nanoparticles, M13 bacteriophage, as reporters and exhibit sensitivities that are up to one-hundred times greater than conventional gold-nanoparticle-based assays.  With Peter Vekilov, we apply our high-throughput imaging methods to study dense liquid protein clusters, which are precursors in which protein crystals subsequently nucleate. Understanding the mechanisms that lead to crystallization in biological settings can help to prevent or treat pathologies, including sickle-cell anemia, gout, and amyloid fibers, that are driven by protein crystallization.