The Culbertson Research Laboratory
Microfluidic devices were first reported in the early 1990s, and research in the area is expanding rapidly. These devices consist of a series of channels etched in glass or molded in various types of plastics. The channels are generally less than 50 μm wide and 10 μm deep - smaller than a human hair. Because complex channel structures can be realized and because the fluids in these structures can be precisely controlled, analytes and cells can be manipulated, processed, separated, and detected all on a single device. The driving forces behind the various sample manipulation, processing, and control steps are electroosmosis, electrophoresis, and pressure differentials.
The unique ability of these devices to integrate sample manipulation and processing operations with separations and analyte detection allows for the efficient automation of chemical analyses and, as such, is driving a paradigm shift in the chemical analysis community. In addition to the automation of chemical analysis, microchips have several other inherent advantages over conventional chemical analysis instrumentation. These advantages include: 1) the ability to perform faster separations with no losses in separation efficiency, 2) lower reagent and sample consumption, 3) less waste production, and 4) the ability to fabricate many parallel systems on the same device.
We are especially interested in developing advanced sample handling, separation, and detection methodologies on microfluidic devices to study protein expression and metabolic pathways in single cells. Following and detecting the changes in protein expression over time in single cells is critical to understanding processes such as cell differentiation, embryology and the evolution of disease states. The ability to identify and quantitate such changes should help 1) in the early diagnosis and successful treatment of diseases like cancer, and 2) in better understanding how complex organisms develop from single cells.
The analysis of such minute, yet complex, samples, however, is extremely challenging. For example, a typical mammalian cell, roughly a cube 15 μm on a side, has a volume of only ~3.5 pL, yet more than 10,000 different proteins are expressed in that cell at any one time. In addition to the sheer complexity of the sample, the concentrations of regulatory proteins - the proteins of most interest - in such a cell are typically in the sub-nM range. To study changes in the expression of these proteins, therefore, highly sensitive detection and powerful separation techniques must be developed for use on these microfluidic devices. To address these challenges we are 1) exploring the use of novel fluorogenic and fluorescent compounds for the derivatization of proteins at low concentrations, and 2) developing multi-dimensional separation techniques to handle the large number of components that need to be separated. Other complicating factors, however, must also be dealt with, such as the propensity of both cells and proteins to adsorb onto the walls of these devices. To minimize such adsorption problems, another area of research that we are pursuing is the development and characterization of new materials both for the fabrication of microfluidic devices and for coating the walls of such devices.