Pan Zehao, Men Yongfan, Senapati Satyajyoti, Chang Hsueh-Chia
Center for Microfluidics and Medical Diagnostics, Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, 46556 Indiana, USA.
Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, Guangdong 518055, China.
Biomicrofluidics. 2018 Aug 16;12(4):044113. doi: 10.1063/1.5048307. eCollection 2018 Jul.
We report a new immersed alternating current (AC) electrospray droplet generation method that can generate monodispersed water-in-oil droplets, with diameters ranging from 5 m to 150 m, in a stationary oil phase. This method offers high through-put, easy size tuning, and droplets with a viscous aqueous phase at high ionic strengths (raw physiological samples). Yet, it does not require coordinated flows of the dispersed/continuous phases or even a microfluidic chip. The design relies on a small constant back pressure (less than 0.1 atm) to drive the water phase through a nozzle (glass micropipette) and a non-isotropic AC electric Maxwell pressure to eject it into the oil phase. Undesirable field-induced discharge and nanojet formation at the tip are suppressed with a biocompatible polymer, polyethylene oxide. Its viscoelastic property favors the monodispersed dripping mechanism, with a distinct neck forming at the capillary tip before pinch-off, such that the tip dimension is the only controlling length scale. Consecutive droplets are connected by a whipping filament that disperses the drops away from the high-field nozzle to prevent electro-coalescence. A scaling theory is developed to correlate the droplet size with the applied pressure, the most important tuning parameter, and to determine the optimum frequency. The potential applications of this technology to biological systems are demonstrated with a digital loop-mediated isothermal amplification experiment, with little damage to the nucleic acids and other biomolecules, but with easy adaptive tuning for the optimum droplet number for accurate quantification.
我们报道了一种新的浸没式交流（AC）电喷雾液滴生成方法，该方法能够在静止的油相中生成直径范围为5微米至150微米的单分散水包油液滴。此方法具有高通量、易于调节尺寸的特点，并且能够生成具有高离子强度（原始生理样品）的粘性水相液滴。然而，它不需要分散相/连续相的协调流动，甚至不需要微流控芯片。该设计依靠一个小的恒定背压（小于0.1个大气压）来驱动水相通过一个喷嘴（玻璃微量移液器），并利用非各向同性的交流电场麦克斯韦压力将其喷射到油相中。通过生物相容性聚合物聚环氧乙烷抑制了尖端处不期望的场致放电和纳米射流的形成。其粘弹性有利于单分散滴落机制，在 pinch-off 之前在毛细管尖端形成明显的颈部，使得尖端尺寸是唯一的控制长度尺度。连续的液滴通过一条鞭状细丝连接，该细丝将液滴从高电场喷嘴处分散开以防止电聚结。我们开发了一种标度理论，将液滴尺寸与施加的压力（最重要的调节参数）相关联，并确定最佳频率。通过数字环介导等温扩增实验证明了该技术在生物系统中的潜在应用，对核酸和其他生物分子几乎没有损伤，但易于自适应调节以获得用于准确定量的最佳液滴数。
