Anal Chem. 2019 Mar 5;91(5):3484-3491. doi: 10.1021/acs.analchem.8b05063. Epub 2019 Feb 15.
We present a method allowing to produce monodisperse droplets with volumes in the femtoliter range in a microchannel on demand. The method utilizes pulsed electric fields deforming the interface between an aqueous and an oil phase and pinching off droplets. Water and xanthan gum solutions are considered as disperse-phase liquids, and it is shown that the method can be applied even to solutions with a zero-shear rate viscosity more than 10-times higher than that of water. The droplet formation regimes are explored by systematically varying the pulse amplitude and duration as well as the salt concentration. The dependence of the process on the pulse amplitude can be utilized to tune the droplet size. To demonstrate the applicability of the electric-field-driven droplet generator, it is shown that the droplets can be used as versatile biological reaction compartments. It is proven that droplets containing a cell-free transcription-translation system execute gene transcription and protein biosynthesis in a timely and programmable fashion. Moreover, it is verified that biomolecules inside the aqueous droplets such as small RNAs can be diffusionally activated from the outside to induce a ligand-driven biochemical switch.
我们提出了一种在微通道中按需生成具有纳升级体积的单分散液滴的方法。该方法利用脉冲电场使水相与油相间的界面变形并挤出液滴。水和黄原胶溶液被视为分散相液体，结果表明，即使对于零剪切粘度比水高 10 倍以上的溶液，该方法也适用。通过系统地改变脉冲幅度和持续时间以及盐浓度来探索液滴形成的模式。该过程对脉冲幅度的依赖性可用于调节液滴的大小。为了展示电场驱动液滴发生器的适用性，我们证明了这些液滴可用作多功能生物反应室。结果证明，含有无细胞转录-翻译系统的液滴可以及时且可编程地执行基因转录和蛋白质生物合成。此外，还验证了水相液滴内的生物分子（如小 RNA）可以从外部扩散激活，从而引发配体驱动的生化开关。
