Hydrodynamically controlled cell rotation in an electroporation microchip to circumferentially deliver molecules into single cells

We present a hydrodynamically controlled, single-cell-rotation method to demonstrate electroporation-mediated molecular delivery in a microfluidic channel. Using a two-inlet geometry to control the carrier-flow profile, cell flow path and angular velocities can be controlled. When the flow-rate ratio between the fluid sheath and cell streams is balanced, fluidic shear occurs near the walls of the channel due to differential flow velocities between the streamlines. Single-cell angular velocities can then be explicitly controlled by using higher flow-rate ratios between the streams. Using sheathing streams with sufficiently high flow-rate ratios between the sheath and sample streams, cells are pinched against the sidewalls of the channel, which results in large degrees of cell rotation. We applied this technique to single-cell electroporation to increase the delivery of small molecules into the cell. Cell orientation was controlled along the length of the microchannel to continuously expose new cell membrane surface area to an applied electric field. Thus, the cell membrane becomes circumferentially permeabilized, resulting in a more efficient and uniform transport of micro- and macromolecules into rotating cells compared to the non-rotating one. Hydrodynamic control of cell rotation offers a new means to enhance intracellular delivery efficiency in single-cell electroporation.