Flow-through Electroporation Using Silver-PDMS Based 3D Sidewall Microelectrodes**Research supported by the National Natural Science Foundation of China (Grant No. 61804007), Fundamental Research Funds for the Central Universities (Grant No. XK1802-4 and No. buctylkjcx06). the Research Funds from Beijing Advanced Innovation Center for Soft Matter Science and Engineering (Grant No. BAIC201607).

Microfluidic electroporators integrated with 3D microelectrodes and working with flow-through manner facilitate high throughput transfection and benefit integration of back-end processing module for the electroporated cells. Here we demonstrate for the first time the flow-through electroporation using 3D sidewall microelectrodes made of silver-PDMS (AgPDMS). Such 3D AgPDMS structure, as a result of low-cost and simple casting process, greatly simplifies the fabrication as compared to existing electroporators incorporating 3D electrodes. Meanwhile, it allows flexible control over the height of the electrode with smooth sidewall profile, which in turn projects rather uniform electric field through deep channel. Delivery of the membrane-impermeable dye of propidium iodide achieves efficiency and viability both at ∼80% for Hela cells, and 79% efficiency with 93% viability for A549 cells. We also show the device capability for plasmid DNA transfection on hard-to-transfect Hela cells. Further, we demonstrate intracellular delivery of nanometer-sized quantum dots (QDs). We believe that the innovative device is a useful addition to the microfluidic electroporation toolbox. It holds great potential as a powerful tool for low-cost and high throughput gene transfection as well as engineered nanoparticles delivery for biological applications.