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Alternating current (AC) dielectrophoresis (DEP) experiments for biological particles in microdevices are typically done at a fixed frequency. Reconstructing the DEP response curve from static frequency experiments is laborious, but essential to ascertain differences in dielectric properties of biological particles. Our lab explored the concept of sweeping the frequency as a function of time to rapidly determine the DEP response curve from fewer experiments. For the purpose of determining an ideal sweep rate, homogeneous 6.08 lm polystyrene (PS) beads were used as a model system. Translatability of the sweep rate approach to $7 lm red blood cells (RBC) was then verified. An Au/Ti quadrapole electrode microfluidic device was used to separately subject particles and cells to 10Vpp AC electric fields at frequencies ranging from 0.010 to 2.0 MHz over sweep rates from 0.00080 to 0.17 MHz/s. PS beads exhibited negative DEP assembly over the frequencies explored due to Maxwell-Wagner interfacial polarizations. Results demonstrate that frequency sweep rates must be slower than particle polarization timescales to achieve reliable incremental polarizations; sweep rates near 0.00080 MHz/s yielded DEP behaviors very consistent with static frequency DEP responses for both PS beads and RBCs. V C 2013 AIP Publishing LLC.

A quadrupole dielectrophoretic microdevice was utilized to examine the ABO-Rh dependencies on erythrocyte polarizations. This important step toward medical microdevice technology would transform key clinical blood tests from the laboratory into the field. Previous work in dielectrophoretic microdevices demonstrated that the large number of ABO antigens on erythrocyte membranes impacts their dielectrophoretic signature at 1 MHz. This work explores the dielectrophoretic behavior of native human erythrocytes categorized by their ABO-Rh blood types and directly compares these responses to the same erythrocyte sample modified to remove the A and B antigens. A β(1-3)-galactosidase enzyme was utilized to cleave the ABO polysaccharide backbone at the galactosidase bonds. The enzymatic reaction was optimized by comparing agglutination of the native and modified blood cells in addition to UV-Vis and HPLC analysis of the reaction effluent for saccharide residues. Next, the dielectrophoretic behaviors of the native and modified erythrocytes were visually verified in a quadrupole electrode microdevice over a frequency range from 100 kHz to 80 MHz. The lower cross-over frequency (COF), which transitions from negative to positive dielectrophoresis, for ABO blood types tested (A+, A-, B+, B-, AB+, O+ and O-) differed over the range from 17 to 47 MHz. The COFs of the corresponding enzyme-modified erythrocytes were also determined and the range narrowed to 29-41 MHz. A second COF in the 70-80 MHz range was observed and was reduced in the presence of the transmembrane Rhesus factor. These results suggest that antigen expression on erythrocyte membrane surfaces influence cell polarizations in nonuniform AC fields.

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She received her B.S. degree in Biological Sciences from Clemson University in 1996 and her M.S. and Ph.D. degrees in Chemical Engineering from Clemson University in 2001 and 2005. Dr. Walters' research involves the development and surface modification of stimuliresponsive and bio-inspired polymeric materials. She has been a member of ASEE since 2002.