Electrokinetic Trapping of Microparticles Using Paper-and-Pencil Microfluidics

Abstract

Preconcentration of microparticles or biological entities to a measurable level is required in many disease detection applications. Motivated by this utilitarian scope, we demonstrate a controlled maneuvering of polystyrene particles on a simple “paper-and-pencil”-based device by exploiting the underlying electrokinetic phenomena with primary contribution from dielectrophoretic (DEP) forces. In sharp contrast to other reported DEP devices, the present configuration does not demand any sophisticated laboratory module for creating a nonuniform electric field, which is an essential requirement in DEP settings. We explore negative dielectrophoresis to trap a 1-µm size polystyrene particle in a low-conductivity suspending medium, at an applied field strength of approximately 10 V/cm. The flexibility of the device design offers controlled and yet localized and selective trapping as per requirements. Furthermore, switching of the trapping direction (negative to positive dielectrophoresis) can be simply achieved by manipulating the conductivity of the medium. Our study brings out an optimum range of the medium's pH for efficient trapping. Considering the potential utilization of this technique, we demonstrate bacterial aggregation, which will be helpful in designing alternative point-of-care diagnostic devices (particularly for sample preconcentration) within resource-limited settings.