Capillary electrophoresis (CE) is a technique used to separate individual components in a mixture, which is often a crucial first step to identifying those components. In short, a very thin fused silica tube called a capillary is filled with buffer and a small amount of analyte is loaded into one end. When a voltage is applied across the capillary, components move through the capillary at different rates, dependent on a variety of properties. My research focuses on developing a capillary electrophoresis technique called capillary isoelectric focusing (cIEF) and our goal is to separate and quantify the proteins in a single cell. This could eventually be used for diagnosing diseases, or finding candidate drug targets (proteins which appear to behave substantially differently in diseases versus non-diseased patients). cIEF separates proteins by their acidity/basicity, also known as their isoelectric point (pI). However, this technique currently suffers from poor reproducibility, likely caused either by protein adsorption onto the capillary walls, or degradation of the coating on the capillary walls. In particular, my present research concerns making new polyacrylamide-based capillary coatings, and evaluating the efficiency and reproducibility of the separations for each coating. If I find a coating which works for reproducible cIEF, then I will begin working on two-dimensional separations, analogous to 2D gel electrophoresis, but with single-cell sensitivity and potentially improved resolution.

The purpose of this study is to create new research tools for characterizing extracellular compounds that are produced by plant endophytes that are difficult to culture. There has been recent evidence that suggest some endophytes produce compounds that are similar to hydrocarbons, which could be useful for making bio-fuels. To detect traces of hydrocarbons, we are using Polydimethylsiloxane (PDMS), which is a polymer material that strongly absorbs organic materials from water, thus concentrating the organics for easier detection. Our procedure involves forming a nanometer thin layer of PDMS on the surface of a Quartz Crystal Microbalance (QCM) crystal and measuring the mass of absorbed organic material as a function of solution concentration. The proportionality constant between absorbed organic material and its solution concentration is the partition coefficients (K). So far, we have been working on how to make uniform nanometer thin PDMS layer on the surface of a QCM crystal. We have found that PDMS and catalyst at 0.5% (weight/volume) in a hexane solvent can create thin layers of PDMS on the QCM crystal when we drop-cast it on a hydrophobic functionalized surface. We are performing further tests of the % weight per volume of the PDMS and catalyst with hexane to ensure we obtain good uniform nanometer thin PDMS layers, which would allow more accurate measurements of K.

Chemical gradients perform an integral role in the cellular behavior of many biological activities. Analysis of the effects of different gradient patterns on cellular responses can help to increase understanding of cellular mechanisms and methods for manipulation of cells within biological systems. In order to perform in vitro cell culture studies, developments in microfluidic technology are being explored due to the precise control of flow rates, use of small amounts of reagents and representative design to in vivo conditions. A novel device has been recently developed which, creating a diffusion gradient perpendicular to the flow direction, can be directly applied to cell cultures in order to monitor cellular response. However, like existing gradient generator designs, this device can only maintain a gradient flow of one concentration. Because of these current constraints, the ability to construct modular components can significantly increase the functionality of microfluidic devices. For this project, the construction of a modular microvalve addition for the gradient generator was designed to provide a method for creation and control of multiple gradient types. The module microvalve was constructed using polydimethylsiloxane (PDMS) molding and an SU-8 mold created through photolithography. In current testing, the use of the designed module microvalve has allowed for the control of different types of gradients within the microfluidic gradient generator. This has enabled the change of gradient solutions and concentrations, during experimentation, while maintaining constant fluid flow in studies with colored dye. The progression of modular microfluidic elements has significant implications to the advancement of microfluidic fabrication and experimentation. Utilizing modular design, microfluidic fabrication times and complexities can be reduced to the production of independent elements that can be joined together to produce progressively more complex devices. Through the expansion of current functions of microfluidic device, microfluidic application towards cellular studies can be significantly advanced.

 Chitin is the second most abundant polysaccharide in nature, and has several applications as a biomaterial ranging from tissue engineering, controlled drug release, to semipermeable membranes for water purification and fuel cells. Although chitin commonly exists as nanofibers in living systems, in vitro preparation of chitin nanofibers is challenging due to its insolubility in common organic solvents. Previous approaches in preparing chitin fibers involve either cumbersome procedures or harsh conditions such as low pH. These approaches not only cause deacetylation or depolymerization of the macromolecule that might change its native properties, but also may raise some environmental concerns. Here, we present the acid free preparation of individual ß-chitin nanofibers precipitated in water from Lithium chloride /N,N-dimethylacetamide. The resulting ß-chitin nanofibers have a 9 nm average diameter and 2-3 µm lengths. We control fiber density with solution concentration, and fiber alignment with flow inside a capillary tube. Further characterization of these chitin nanofibers is currently underway.

Molecular self-assembly of thiols onto gold is a powerful method for surface modification in biomaterials research. For instance, thiolated sugars can form glycan-functionalized surfaces for carbohydrate microarray and biosensor fabrication. To illuminate glycosylated surface composition and structure, we utilized a model system consisting of mixed-thiol self-assembled monolayers (SAMs) of a synthetic tetrasaccharide and oligo(ethylene glycol) on gold(111). Here, we show that atomic force microscopy (AFM) analysis of these mixed SAMs reveals two distinct domains that appear to coalesce and phase separate over time. X-ray photoelectron spectroscopy demonstrates a relationship between the compositions of sugar on the surface to its molar ratio in solution. These results suggest that clustering of sugar is thermodynamically favorable, occurring within mixed sugar/oligo(ethylene glycol) SAMs.

We report on a novel digital microfluidic device capable of achieving droplet transport using vertical vibration and curved hydrophilic rungs patterned onto a hydrophobic surface. The original Surface Ratchets were implemented using microscopically rough features on polydimethylsiloxane (PDMS) or silicon with a hydrophobic coating. Flat Surface Ratchets take advantage of periodic asymmetric wetting barriers by patterning the wettability of a substrate with self-assembled monolayers (SAMs). We report two novel device fabrications, a hydrophilic trimethylsilanol SAM patterned onto either a hydrophobic perfluorooctyltrichlorosilane (FOTS) or dodecanethiol SAM. Transport of a 10 μl droplet is demonstrated by applying vertical sinusoidal vibrations with an electromagnetic speaker with amplitudes low as 37 μm at 82 Hz. The ease of Flat Surface Ratchet fabrication, a simple wettability pattern, makes the technology implementable on a massive range of substrates opening up numerous potential applications. For example, the trimethylsilanol-FOTS Flat Surface Ratchet is an optically flat device, yielding a fully transparent device if fabricated onto glass. Such a device could be easily integrated onto a car’s windshield, and droplet transport could potentially be driven by the natural vibrations of a car.