Tunable Electroosmosis-Based Femto-Liter Pipette: A Promising Tool toward Living-Cell Surgery

Single-cell analysis has attracted increasing attention because of cell heterogeneities. Various strategies have been developed for analyzing single cells, but most of these analytical processes kill the cells. Tools that can qualitatively and quantitatively measure the cellular contents without killing the cell are highly demanding because they enable us to conduct single-cell time-course studies (e.g., to examine how a cell responds to a therapy before, during, and after a treatment). Here we develop a femto-liter (fL) pipet to serve this purpose. To ensure that we can accurately and precisely pipet fL solutions, we fill all conduits with liquid and use an electroosmotic pump (EOP) as the driving force to facilitate withdrawal of cellular contents from single cells. We tentatively term this device an EOP-driven pipette or EDP. We characterize the EDP for accurately and precisely withdrawing solution from ∼250 fL to 80 nL; a volume range that covers the applications for most types of cells. To demonstrate the feasibility of utilizing the EDP for a single-cell time-course study, we utilize the EDP to take the cellular contents out at different times during the course of a zebrafish embryo development for cholesterol measurements. More than 50% of the embryos survive after each pipetting and analysis step, and this number will increase considerably as we improve our cell manipulation skills and reduce the pipet-tip diameter. We expect this EDP to become an effective tool for single-cell time-course studies.