Microfluidic cell electroporation using a mechanical vavle

Introduction Electroporation is a technique that applies electric field to transiently permeabilize the cell membrane to deliver impermeant molecules into cells. Due to its wide applications to gene/drug delivery, electroporation has been adapted in microfluidic devices by fabricating microscale electrodes and structures that apply short electric pulses [1-3]. The fabrication of microscale electrodes presents a difficulty for lowering the cost of these microfluidic chips. Furthermore, an electric pulse generator is needed to generate pulses with durations ranging from microseconds to milliseconds. The pulse generator also adds to the cost and complexity of the overall system. In recent work, microfluidic channels with geometric variation were applied to electroporation and electrofusion of flowing cells using a common dc power supply [4, 5]. While the technique doesn’t require a pulse generator and microfabricated electrodes, it cannot be applied to in situ electroporation of adherent cells. The adhesion to the substrate can be important for cellular functions of adherent cell types. Thus electroporating cells while they adhere to the substrate is often desired due to the minimum disturbance to the cell culture. Here we demonstrate a microfluidic technique that electroporates both suspended cells and cells adhering to the bottom of a microfluidic channel using a common dc power supply, taking advantage of a fast-response microscale mechanical valve [6]. The mechanical valve turns on/off a dc electric field established in a microfluidic channel rapidly by physically connecting/separating the ionic buffer. By virtue of that, we are able to effectively produce electric pulses of milliseconds using this approach. We investigate the effects of the valve dimensions, the actuation pressure, and the voltage applied on the performance of the valve in terms of pulse generation. We also examine the viability of cells after electroporation using the device and demonstrate the electropermeabilization of cells by an impermeant dye SYTOX green.