Soumya S. Keshavamurthy1, Adrienne R. Minerick1
1Dave C. Swalm School of Chemical Engineering, Box 9595
Mississippi State University, Mississippi State, MS 39762
Medical lab work, such as blood testing, will soon be near instantaneous and inexpensive via capabilities enabled by the fast growing world of microtechnology. Lab-on-a-chip systems having the capacity to perform a variety of tasks ranging from DNA analysis to protein recognition and can also be catered to point-of-care medical diagnostic tools. Lab-on-a-chip devices commonly utilize electrokinetics to move analytes because electric fields are versatile and can be precisely controlled for specific, quantifiable analyte responses. Furthermore, devices employing electric fields can eventually be simplified to only require a battery for power – a key characteristic for true portable diagnostic devices. One type of electrokinetics, dielectrophoresis, uses spatially nonuniform AC electric fields, which depends on the polarizability of dielectric particles or erythrocytes. Previous research by the authors has shown that blood types respond differently in AC dielectrophoretic fields: type A+ had the maximum deflection from high field density followed by type B+ and AB+, where as type O+ had an attenuated response in the nonuniform electric field . These results suggest that spatial separation in the electric field depends on the blood type antigen expressed on the surface of the erythrocytes. This attribute forms the foundation for the continuous flow, DC dielectrophoretic research presented here.
In this work, no electrodes are placed within the test channel, thus simplifying fabrication. Instead, a DC electric field is applied around an insulating obstacle in the microfluidic channel, which creates a spatially non-uniform electric field. This technique is commonly referred to as DC dielectrophoresis or electrodeless dielectrophoresis. A number of insulating obstacles have been explored by other researchers that comprise different shapes (rectangle, triangle, and saw-tooth) and materials (PDMS) / fluids (oil). In our work, we utilize PDMS obstacles of rectangular, trapezium and semi-circle geometrical configurations on the order of 100 microns in breadth. Device dimensions were optimized by evaluating the behaviors of fluorescent polystyrene particles of three different sizes roughly corresponding to the three main components of blood: platelets, erythrocytes and leukocytes. This work provides the operating conditions for which size dependent blood cell DC-dielectrophoresis can be performed. The optimized device was used for continuous separation of erythrocytes according to blood types. The design enables collection into specific channels based on the cells deflection from the high field obstacle. The port having maximum number of cells corresponds likely to a specific blood type. This developed technique can be directly applied for use in portable blood diagnostic devices for easy, accurate and rapid analysis.
1. Srivastava, S. K.; Daggolu, P. R.; Burgess, S. C.; Minerick, A. R.; Electrophoresis (in press) 2008