Electrorotation of HL-60 cells uptake of metal and dielectric nanoparticles in a stationary AC electric field

Electrorotation has become a very powerful diagnostic technique for measurement of dielectric properties of cells. However, only few papers investigated in the electric-induced rotation of particles in a stationary alternating (AC) electric field instead of a rotating electric field. In this study, a microchip comprised top grounded electrode, flow chamber and bottom chess-type electrode arrays to construct a stationary nonuniform AC electric field for manipulation of cells by dielectrophoretic (DEP) force. We aimed at the discrepancy on electrorotation between metal (Au) and dielectric (SiO₂) nanoparticles uptaken by the human promyelocytic leukemia cells (HL- 60). As experimental results, both the percentage of cells in rotation and the range of rotational frequency for uptaken-Au-nanoparticles cells were higher and wider than the case of SiO₂ nanoparticles, respectively. In addition, the cell membrane for a continued rotating cell could be deformed and broken after 30 to 40 minutes. According to the rotational spectra (ROT), the membrane capacitance and membrane conductance of HL-60 cells can be extracted, 9.95 mF/m² and 1460 S/m², respectively. In general, the electrorotation of cells in a stationary AC electric field can be attributed to the highly nonuniform electric field and nonuniform dispersion of nanoparticles within cells; therefore, the electrical properties of uptaken nanoparticles and the aggregation phenomenon have significant influences on resulting electrical torque, the membrane capacitance and membrane conductance of HL-60 cells can be calculated in this method without a rotating electric field excited by poly-phase AC voltages.