Size fractionation of graphene oxide sheets by electron beam-addressing localized electrophoresis

Size fractionating of graphene oxide (GO) into micro- to nano-scaled fractions is a crucial process for assessing GO size-dependent physiochemical effects on living cells. However, due to the difficulty in dynamically observing interactions between size-fractionated GO and target cells, conflicting analytical reports about the biocompatibility of size-controlled GO present challenges to researchers’ understanding. Thus, it is necessary to have a dynamic size fractionation system to manipulate the desired GO sizes for the in-situ observation. Here, we present an electrokinetic size fractionation system for two-dimensional materials with surface charges by positioning an electron beam (EB)-induced virtual cathode (VC), which can generate programmable electric fields on a dielectric silicon nitride (SiN) surface. Also, we propose a size fractionation mechanism using two different external forces: electrophoretic force and electroosmotic flow-induced drag force acting on negatively charged GO. In addition to making a numerical simulation for the electrokinetic force field, we experimentally observe the transient migration velocities of GO sheets with the sheet area of 5–50 µm 2 that are attracted to the center of a ring-shaped VC and then repulsed from the edge of the VC. In the repulsion step, importantly, the migration velocities of the GO sheet are found to increase as the GO sheet area is smaller. Moreover, migration directions of the GO sheet are locally manipulated by dynamically positioning the VC relative to the GO sheet. We expect our system will move towards an accurate understanding of the interfaces between size-fractionated GO and the targeted cells.