(250b) Dielectrophoretic Separation of Large Microscale Particles (dp>5 um) By Exploiting Charge Differences

Electrokinetics is the family of phenomena that depend on the electrical double layer. Electrokinetic techniques are one of the main pillars of microfluidics, due to their ease in application. Electric-field driven technique such as electroosmosis, electrophoresis and dielectrophoresis have been successfully used for the analysis, sorting and separation of a wide array of bioparticles, in applications than range from environmental assessments to biomedical and clinical analysis. In this current project, efforts have been made to analyze the equilibrium between the electrophoretic, electroosmotic and dielectrophoretic forces and how this equilibrium is affected by particle size. As the motion of larger particle under electric fields has yet to be fully characterized, the primary focus has been particles with diameters ranging from 5-10 microns. In theory, these “larger” particles should be easier to “trap” in our insulator-based dielectrophoresis (iDEP) systems when compared to smaller particles, since DEP force depends on particle volume, however, this is not the case. Throughout this study an iDEP microchannel, with an array of cylindrical insulating structures and direct current electric fields have been employed. Results from current and preliminary experiments have showed that larger carboxylated polystyrene particles (diameter > 5 mm) require much higher voltages than expected and also have shown to move very fast through such iDEP systems. Employing suspending media with conductivity of 15-20 mS/cm and pH of 6-7, under applied fields between 400 V/cm and 1500 V/cm, the 5-mm, 7-mm and two types of 10-mm polystyrene particles were observed to become immobilized due to negative electrophoretic trapping. In addition, it our experiments have reveled that the amount of surface charge of the particles may also have an impact of the ability to trap these larger particles and will be further explored as the project moves forward. The results of this project will hopefully be able to help explain why these larger particles do not behave according to theory. The recent finding in reference to amount of surface charge also has the potential to become another method by which biological particles can be separated through the use of iDEP.