Prof. Chris Culbertson, Kansas State University

Small Volume Biological Sampling, Fluid Handling, and High Efficiency Separations, on Microfluidic Devices

Microfluidic devices are dramatically changing the face of bioanalytical chemistry. These devices have the unique capability of integrating a variety of chemical processing and analysis steps with single cell culturing, handling and transport. Many of the microfluidic devices developed for cell work are fabricated from poly(dimethylsiloxane) (PDMS). PDMS is generally used because of its high oxygen permeability and biocompatibility. Unfortunately, however, electrophoretic separations on PMDS-based microfluidic devices are generally much poorer than on glass microfluidic devices especially for hydrophobic molecules (e.g. rhodamine and BODIPY® labeled biomolecules). To improve the separation of these analytes we have developed both covalent and non-covalent coatings based upon sol-gel chemistry and surfactants, respectively, that result in very high efficiency, diffusion limited separations. We will discuss the results of these various coating methods.

In addition to these separation improvements we have also been developing methods to improve fluid control and injections on microfluidic devices. These methods are based upon the use of applying electric fields external to the microfluidic channels. Changing the voltage applied to a patterned electrode that is separated from the fluidic network by a thin PDMS film produces local, transient disruptions of the EOF. We have exploited this phenomenon to produce analyte injections at the intersection of two channels on a microchip. We will describe the fabrication of such devices and demonstrate the effect of potential change (magnitude and sign), electrode size, buffer pH and buffer concentration on the flow characteristics at the channel intersection. Performing injections using these external fields significantly reduces the electrokinetic biasing generally seen with a gated injection.

Finally, we have been developing methods to address small volume biological sampling challenges. One such challenge is the collection of aphid salivary secretions. Aphids are small, soft-bodied insects that are major crop pests and plant virus vectors. Aphids salivate into plants prior to feeding to suppress the plant's innate immune system. Unfortunately because of the small volume of saliva injected on one has been able to successfully identify any of the salivary components. We are attempting to use microfluidic devices as leaf mimics to identify for the first time some of these salivary components.

For more information contact Dr. Donald Doyle (404-385-0631).