Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 150296

150296 - Frequency-Dependent Electro-Deformation for Analysis of Individual Variability in Human Blood 

Introduction:

     Dielectrophoresis (DEP) is analyzed by the application of Maxwell’s equation where particles move in the medium in a response to changes in the electric field gradient.  DEP has been widely used in microfluidic systems for label-free sorting, enrichment, and characterization of a variety of micro- and nanoscale biological particles and engineered particles. A particular application of DEP technique is the testing of the deformability of biological cells, such as red blood cells (RBCs), where cells move toward the higher field strength due to DEP and spontaneously cell membranes are stretched uniaxially due to electro-deformation. Degree of cell electro-deformation can be quantified by elliptical shape factor (ESF). The application of electro-deformation is utilized in testing on different types of cells such as RBCs, mammalian cells, or cancer cells. Conventionally, alternating current (ac) electric fields at a specific frequency are used. However, with applied electric force the elongation of cell shape changes in a frequency-dependent way. Studies show that the frequency-dependent electro-deformation (or electro-deformation spectroscopy, EDS) of human cells are distinct from animal cells in both magnitude and frequency. 

     In this paper, we describe the application of EDS as a new characterization method that detects individual variability of human blood samples. We utilized three normal blood samples where EDS analysis is performed under a set of frequencies with the same field magnitudes. 

 

Methodology:

     The microfluidic device for the EDS analysis consists of two parts: an indium tin oxide microelectrode array (44 μm gap) on a 0.7mm thick glass substrate and a polydimethylsiloxane channel with an inlet and outlet of 3mm and 1 mm respectively. The channel was primed with the working medium to allow cells to spread evenly in the channel. The medium is made of 0.3% (w/v) dextrose and 8.5% (w/v) sucrose. The conductivity of the medium was adjusted to 400mS/cm with phosphate-buffered saline.

     Two finger blood samples were obtained from donors and one sample from a blood bank. To perform EDS, 1ml of each blood sample was diluted in 500 ml of working medium. A 5 ml cell suspension was added into the channel. Then sine wave signals of root mean square voltage of 2V at the range of frequencies from 1 MHz to 15 MHz were used to induce electro-deformation. Cell images were captured with an inverted microscope under 20× magnification, with contrast improvement achieved by adding a 414 nm bandpass filter in the optical pathway. Images were analyzed with ImageJ software by fitting individual cells in the ellipse. The ESF is equal to the ratio of a to b, the major and minor axes of the ellipse. These data were compared between three samples.

 

Results:

Before performing EDS, red blood cells in all three samples were undeformed, and their ESFs were 1.25 for sample 1, 1.28 for sample 2, and 1.2 for sample 3. The average ESF at different frequencies was calculated and analyzed. The results demonstrate that the deformation of the cells is highly dependent on the frequency. Generally, all samples showed marked deformation at lower frequencies (< 9 MHz). Deformation decreases as frequency increases. However, while they follow a similar nonlinear pattern, the details are different. 

     Among the three samples, sample 1 has the lowest ESF, suggesting the least deformability of cell membranes among the samples under testing. In contrast, sample 2 with the highest ESF values indicates the highest cell deformability. The frequency of the peak deformation is found to be around 4 MHz for sample 1, 3 MHz for sample 2, while a relatively wide frequency range 3-6 MHz for sample 3. These results clearly demonstrated the individual variability in cell electromechanical properties. 

 

Conclusion:

In the end, we demonstrated that EDS is a useful tool to detect individual variability through ESF analysis of RBC elongation. Detailed mathematical models of cell electro-deformation will enable in-depth analysis of cell electromechanical properties. 

Presenting Author: Liliana Ponkratova Florida Atlantic University

Presenting Author Biography: Liliana Ponkratova is a master student in Biomedical Engineering at Florida Atlantic University. She has B. S. degree in Biotechnology and Bioengineering from V. N. Karazin Kharkiv National University. Current research interests include microfluidics and electrodeformation techniques and their applications in single cell biomechanical and electrical characterization.

Authors:

Liliana Ponkratova Florida Atlantic University
Hongyuan Xu Florida Atlantic University
E Du Florida Atlantic University