Continuous Redirection and Separation of Microbeads by Faradaic Ion Concentration Polarization

Herein we report that faradaic ion concentration polarization (fICP) can be used to sort and separate micron-scale objects within a bifurcated microelectrochemical device. In fICP, a bipolar electrode (BPE) is activated by a driving voltage, which results in formation of an ion depletion zone (IDZ) and an ion enrichment zone (IEZ). By judicious control of the placement of the BPE and control of the driving voltage, the IDZ and IEZ can be manipulated in a way that directs charged microbeads into a particular channel of the microelectrochemical device. The key findings are threefold. First, similar to 100% microbead redirection and separation may be achieved by fICP. Second, the tracking of microbeads as they traverse the channel length permits visualization of local variations in electroosmotic flow (EOF). Third, variations in solution conductivity in different regions of the channel lead to differences in EOF that exert a significant influence over microbead trajectory.