Investigation of human malignant cells by electrorotation C. Dalton 1 , S. Adamia 2 , L. M. Pilarski 2 and K. V. I. S. Kaler 1 1 Department of Electrical and Computer Engineering, University of Calgary, AB, Canada 2 Department of Oncology, University of Alberta and Cross Cancer Institute, Edmonton, AB, Canada Abstract: Dielectrophoresis (DEP), traveling wave dielectrophoresis (TWD) and electrorotation (ROT) are established electro-kinetic methods that can be usefully applied for the selective and controlled manipulation, isolation, concentration, separation and characterization of electrically polarizable particles, such as intact cells. Using a custom integrated fluidic microchip, capable of DEP, TWD and ROT measurements, the differences in the frequency dependent dielectric properties of malignant cells obtained from peripheral blood (PB) of patients with multiple myeloma (MM) were investigated. Utilizing these electro-kinetic phenomena will facilitate simultaneous isolation and characterization of different cell populations of PB from patients. Furthermore, the ability to detect and identify malignant cells based on their unique and precise dielectric properties will enable rapid and cost effective detection of impending relapse and/or progression of the disease in addition to the monitoring of response to therapy. Introduction In the last decade, miniaturized ‘lab-on-a-chip’ systems have become readily available [1]. The ability to interact at the scale of biological processes opens up many new avenues of research, such as the rapid and non-invasive identification, characterization and analysis of micrometer scale particles from microorganisms to larger mammalian cells, or nanometer scale structures, such as viruses, nucleic acids (DNA, RNA) or proteins [2,3]. Characteristic electric and dielectric properties are of particular interest in present-day applications of disease diagnosis and monitoring, physiological pathological research, cellular engineering and environmental study [4,5]. Microfluidic cellomic devices, incorporating the measurement of electric and dielectric properties, allow the selective segregation and purposeful manipulation of micro- or nano-structures of living organisms [6,7]. The focus of this paper is on the phenomenon of dielectrophoresis (DEP), which was first defined by Pohl as the motion of neutral but polarizable particles subjected to non-uniform electric fields [8]. A non- uniform electrical field induces a dielectrophoretic force that causes particle conveyance, depending on its polarization state, either towards electric field maxima (positive DEP) or minima (negative DEP). A phase varying, non-uniform electric field implemented in a rotating configuration causes particle rotation (electrorotation, ROT). When such a field is linear in arrangement, then linear particle conveyance is observed (traveling wave dielectrophoresis, TWD). DEP provides precise measurement and sensitivity for the detection and separation of cells with differing dielectric properties, without any need for labeling [9,10]. The three electrokinetic effects have been extensively studied, both from a theoretical and an experimental perspective, and have been applied in a variety of biotechnological and clinical applications requiring cell manipulation [11-13]. Integrated systems that combine more than one of the dielectrophoretic responses on a single microchip have been the focus of recent research [14-16]. Combining the three techniques onto one device has the potential to overcome problems associated with ’real’ world sample pre-treatment that affects most micro- fluidic systems [17] by implementing sample processing “on-chip”, through the ability to selectively trap and move cells in heterogeneous populations. In this work we use a previsously reported combined DEP-TWD-ROT chip [14] to investigate the ROT characteristics of malignant cells from peripheral blood (PB) of patients with multiple myeloma (MM). MM is an incurable cancer with a median survival rate of 3-4 years post diagnosis. Thus far, neither consistent genetic abnormalities, nor the molecular basis of the disease, have been identified. Clinically, MM has been considered as a disease of the bone marrow. However, molecular studies performed by many groups, including CCI, have revealed a population of abnormal B lymphocytes in the PB of patients with MM [18,19]. Lymphocytes are a class of leukocytes that regulate the body’s acquired immunity to foreign cells and antigens. Lymphocytes, including B cells, are the smallest among the white blood cells and are slightly larger than erythrocytes. The size of inactive lymphocytes ranges from 6 to 9 μm in diameter. Activated cells, known as ‘large’ lymphocytes, are 9 to 15 μm in diameter, and make up 3% of lymphocytes in PB. Lymphocytes are charecterized by a round, densely stained nucleus which is surrounded by a non-granular cytoplasm (Figure 1).