High-throughput optical injection of mammalian cells using a non-diffracting beam in a microfluidic platform

Femtosecond photoporation is an optical, non-invasive method of injecting membrane impermeable substances contained within the surrounding medium into cells. The technique typically addresses individual cells in a static monolayer. While this gives excellent selectivity, it can be time consuming or impractical to treat larger samples. We build on previous work using a microfluidic platform, which allows for a suspension of cells to be dosed with femtosecond light as they flow through a microfluidic channel. A reusuable quartz chip is designed with an 's'-bend with facilitates the delivery of a 'non-diffracting' femtosecond Bessel beam along the centre of the channel. By implementing off-chip hydrodynamic focusing, cells are confined to the central region of the channel and pass along the Bessel beam core where they are photoporated. This new parallel approach allows for higher flow rates to be used compared to the previous, orthogonal, design whilst maintaining the necessary dwell time in the Bessel beam core. Optical injection of the cell membrane impermeable stain propidium iodide has been successful with two cell lines. These have yielded viable injection efficiencies of 31.0+/-9.5% Chinese hamster ovary cells (CHO-K1) and 20.4+/-4.2% human promyelocytic cells (HL60) with a cell throughput of up to 10 cells/second. This marks an order of magnitude increase compared to the previous microfluidic design.