Tensiophoresis: Label Free Droplet Sorting in Surfactant Microgradients

1236764 PI：BasuCapillary迁移是一种众所周知的现象，是当连续相呈现界面张力（IFT）梯度时液滴的定向输送。 由于温度和IFT之间的耦合相对较弱，因此所产生的力和迁移速度受到限制。 本计画的目的是研究液滴在表面活性剂浓度梯度中的毛细迁移。 这种方法利用微流体技术在微通道中产生精确的二维表面活性剂梯度，垂直于流动方向，然后用于控制液滴的毛细管迁移。由于表面活性剂浓度和IFT之间的强耦合，这可以在不加热液滴的情况下实现大于两个数量级的毛细管力和因此显著的迁移速度。一个新的特点是，液滴的迁移速度与其界面性质成反比，而界面性质又强烈依赖于其化学组成。 因此，张力电泳具有独特的能力，可以通过其化学成分被动地对液滴进行分类，而无需额外的化学标签或致动器。 该项目主要是实验性的，将通过以下具体目标建立对该现象的基本理解并展示其应用：1）设计微流体装置，其产生表面活性剂浓度的线性和对数梯度; 2）验证液滴迁移在由表面活性剂浓度、几何长度尺度和粘度确定的几种操作制度下的缩放; 3）研究表面活性剂性质和动力学对运输机制的影响;以及4）使用张力电泳法基于蛋白质浓度进行无标记液滴分选。 生命科学行业正朝着逐步缩小反应体积的方向发展，以降低高通量筛选的成本和环境足迹。 与常规技术相比，在微滴中进行这样的测定可以将反应体积减少3-6个数量级。 这大大减少了试剂消耗，提高了测定通量，并实现了传统工具无法实现的新型生物测定（例如，单细胞）。这项研究将有助于第一个无标记的方法来分选液滴反应器的化学成分的基础上。 鉴于高通量筛选在现代生物研究中的重要性，这项技术最终将有利于医学诊断，环境分析和基础科学。在基本层面上，该项目有助于两个科学领域。 在多相过程背景下，它将发现控制和应用毛细迁移现象的新方法，并为研究液液界面非平衡物理化学流体动力学搭建独特的实验平台。 在分离科学的背景下，张力电泳可以被认为是一类新的光传输现象，其能够根据液滴的界面性质对液滴进行分选。 这项工作的跨学科性质将为研究生提供一个宝贵的培训环境，包括通过韦恩州SURA计划招募的妇女和代表性不足的少数民族。

1236764PI: BasuCapillary migration, a well-known phenomenon, is the directed transport of a droplet when the continuous phase presents a gradient in interfacial tension (IFT).The vast majority of prior literature has focused on thermocapillary migration, where the IFT gradient is due to a temperature profile. Due to the relatively weak coupling between temperature and IFT, the resulting forces and migration velocities are limited. The objective of this project is to investigate the capillary migration of droplets in gradients of surfactant concentration. This approach exploits microfluidic techniques to generate precise two-dimensional surfactant gradients in microchannels, orthogonal to the direction of flow, which are then used to control the capillary migration of droplets. Due to the strong coupling between surfactant concentration and IFT, this can achieve greater than two orders of magnitude capillary force and hence substantial migration velocities without heating the droplet. A novel feature is that the migration velocity of the drop is inversely related to its interfacial properties, which in turn depends strongly on its chemical composition. As a result, tensiophoresis has the unique ability to passively sort droplets by their chemical contents, without additional chemical labels or actuators. This project, primarily experimental in focus, will build a fundamental understanding of the phenomenon and demonstrate its application through the following specific aims: 1) Design microfluidic devices which generate linear and logarithmic gradients in surfactant concentration; 2) Verify the scaling of droplet migration over several operational regimes determined by surfactant concentration, geometric length scales, and viscosity; 3) Investigate the impact of surfactant properties and dynamics on transport regimes; and 4) Use tensiophoresis for label-free droplet sorting based on protein concentration. The life sciences industry is moving towards progressively smaller reaction volumes in order to reduce the costs and environmental footprint of high throughput screening. Performing such assays in microdroplets can reduce reaction volumes by 3-6 orders of magnitude compared to conventional technology. This dramatically reduces reagent consumption, improves assay throughput, and enables novel types of biological assays (for example, single cells) not possible with conventional tools. This research will contribute the first label-free method for sorting droplet reactors based on their chemical composition. Given the critical importance of high throughput screening in modern biological research, this technology will ultimately benefit medical diagnostics, environmental analysis, and basic science. On the fundamental level, this project contributes to two scientific areas. In the context of multiphase processes, it will discover novel ways to control and apply the phenomenon of capillary migration, and build a unique experimental platform for studying non-equilibrium physicochemical hydrodynamics at liquid-liquid interfaces. In the context of separation science, tensiophoresis can be considered a new category of phoretictransport phenomena which enables the sorting of liquid droplets on the basis of their interfacial properties. The interdisciplinary nature of this work will provide a valuable training environment for graduate students, including women and underrepresented minorities recruited through Wayne State SURA program.