Tensiophoresis: Label Free Droplet Sorting in Surfactant Microgradients

1236764PI：Basu毛细管迁移是一种众所周知的现象，它是当连续相呈现界面张力梯度(IFT)时液滴的定向传输。以前的大多数文献都集中在热毛细管迁移上，其中IFT梯度是由温度分布引起的。由于温度和IFT之间的耦合相对较弱，所产生的力和迁移速度是有限的。本项目的目的是研究表面活性剂浓度梯度下液滴的毛细迁移。这种方法利用微流控技术在微通道中产生与流动方向垂直的精确的二维表面活性剂梯度，然后用于控制液滴的毛细迁移。由于表面活性剂浓度和IFT之间的强耦合，这可以实现大于两个数量级的毛细管力，从而在不加热液滴的情况下实现实质性的迁移速度。一个新的特征是液滴的迁移速度与其界面性质成反比，而界面性质又强烈地依赖于其化学成分。因此，张力渗透技术具有独特的能力，可以根据液滴的化学成分对液滴进行被动分类，而不需要额外的化学标签或致动器。该项目主要是Focus实验，将建立对这一现象的基本理解，并通过以下具体目标展示其应用：1)设计在表面活性剂浓度中产生线性和对数梯度的微流体装置；2)验证液滴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模式下的规模性迁移；3)调查表面活性剂的性质和动力学对传输模式的影响；以及4)使用张力电泳法进行基于蛋白质浓度的无标签液滴分类。生命科学行业正朝着反应体积逐渐变小的方向发展，以降低高通量筛选的成本和环境足迹。与传统技术相比，在微滴中进行这种分析可以将反应体积减少3-6个数量级。这极大地减少了试剂消耗，提高了分析吞吐量，并实现了传统工具无法实现的新型生物分析(例如，单细胞)。这项研究将有助于首次基于液滴反应器的化学成分对其进行分类的无标签方法。鉴于高通量筛选在现代生物学研究中的关键重要性，这项技术最终将造福于医学诊断、环境分析和基础科学。在基本层面上，该项目在两个科学领域做出了贡献。在多相过程的背景下，它将发现控制和应用毛细管迁移现象的新方法，并为研究液-液界面的非平衡物理化学流体力学建立一个独特的实验平台。在分离科学的背景下，张力渗透可以被认为是一种新的磷光传输现象，它能够根据液滴的界面性质对液滴进行分类。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，包括通过韦恩州立大学SURA计划招聘的妇女和代表性不足的少数族裔。

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.