We present a systematic study of the electrophoretic migration of protein fragments (10-200 kDa) in dilute-polymer solutions using microfluidic chips. The electrophoretic mobility and dispersion of protein samples were measured in a series of monodisperse polydimethylacrylamide (PDMA) polymers of different molecular weights (243, 443 & 764 kDa, polydispersivity index = 2) with varying concentrations. Experiments were also performed in PDMA solutions with a polydispersivity index of about 5 and in mixtures of polymers with different molecular weights. The polymers solutions were characterized using rheometry and optical techniques. Prior to its loading onto the microchip, the polymer solution was mixed with known concentrations of SDS surfactant and staining dye. The SDS-denatured protein samples were electrokinetically injected, separated and detected in the microchip using electric fields ranging from 100 to 300 V/cm.

Our results show that the electrophoretic mobility of protein fragments decreases exponentially with the concentration c of the polymer solution. The mobility was found to decrease logarithmically with the molecular weight of the protein fragment. In addition, the mobility was found to be independent of the electric field in the separation channel. The results appear to suggest that the denatured protein molecules migrate as rigid rod-like molecules. The migration mechanism for protein molecules will be discussed using polymer physics and hydrodynamic drag arguments.

The protein migration was found to depend strongly on the SDS concentration in the polymer solution. Moreover, the optimal concentration of SDS depends on the polydispersity of the PDMA polymer. Specifically, repeated injection of protein samples through a single load of polymer solution was achieved using the optimized value of the SDS concentration. A simple mass balance analysis is used to explain the behavior. The results from experiments using a matrix composed of polyethylene oxide (PEO) and PDMA-PEO blends of varying composition will also be presented.

Refreshments will be served following the seminar.

If you'd like to meet with Prof. Tripathi during his visit, please contact Meredith Leach (x4-2655 or leach at egr.uri.edu).