(516c) Investigating the Impact of Low Concentration Surfactant on Red Blood Cell Dielectrophoretic Responses

Red blood cell dielectrophoretic responses have been extensively studied for blood typing, sepsis and circulating tumor cell separations. Surfactants are a common pretreatment to prevent sticking within dielectrophoretic microdevices. In this study, the dielectrophoretic motion of untreated human erythrocytes (red blood cells, RBCs) were compared to RBCs treated with low concentrations of Triton X-100, which is a widely used nonionic surfactant to solubilize integral membrane proteins. However, at relatively low concentrations, this surfactant has been shown to effectively stabilize cells against osmolysis. This biphasic behavior has not been fully understood, especially within cells subjected to AC electric fields. The objective of this work is to characterize the interaction between Triton X-100 at low concentrations (0.07-0.22mM) and the red blood cell membrane by quantifying changes in the cell’s dielectrophoretic crossover frequency (f_CO). The AC frequency at which cells change the direction of their movement from negative DEP to positive DEP was determined by applying a 5 V_pp signal with a frequency sweeping from 700 to 300 kHz in four pairs of converging triangular (planar Cr/Au) electrodes. At relatively low concentrations (0.07mM), the crossover frequency f_CO was lower compared to untreated RBCs. The f_CO for the control cells averaged 488 kHz, while the treated cells' f_CO was 390 kHz, suggesting that at 0.07mM Triton X-100, the relative membrane permittivity was increased. A plausible mechanism for the amphiphilic surfactant is insertion into the bilayer which alters ion permeability. Altered ion permeability would cause asymmetric component distribution between the outer and inner membrane surfaces disrupting the ion concentration equilibrium between the interior and exterior of the cell membrane. As the concentration of the surfactant increased to 0.14mM, cells began to exhibit negative-DEP during the entire experiment, while others exhibited a f_CO of390 kHz. At this concentration of Triton X-100, cell viability was not compromised. Thus, experiments were performed to determine cell membrane integrity after two hours of treatment. When the concentration of the Triton X-100 reached the critical micelle concentration (0.18 to 0.22 mM), cells uniformly exhibited negative-DEP over the entire frequency range. This work provides mechanistic understanding into the chemical interactions between surfactants and cell membranes that can subsequently be exploited to enable precise control for electrokinetic microdevice separations and operation.