Soft Materials Laboratory, Institute of Materials, École Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland.
Lab Chip. 2018 Dec 4;18(24):3903-3912. doi: 10.1039/c8lc01000e.
Emulsion drops are frequently used as vessels, for example, to conduct biochemical reactions in small volumes or to perform screening assays at high throughputs while consuming minimal sample volumes. These applications typically require drops that do not allow exchange of reagents such that no cross-contamination occurs. Unfortunately, in many cases, reagents are exchanged between emulsion drops even if they have a low solubility in the surrounding phase, resulting in cross-contaminations. Here, we investigate the mechanism by which hydrophilic reagents are transported across an oil phase using water-oil-water double emulsion drops as a model system. Remarkably, even large objects, including 11 000 base pair double-stranded circular DNA are transported across oil shells. Importantly, this reagent transport, that is to a large extent caused by aqueous drops that spontaneously form at the water-oil interface, is not limited to double emulsions but also occurs between single emulsion drops. We demonstrate that the uncontrolled reagent transport can be decreased by at least an order of magnitude if appropriate surfactants that lower the interfacial tension only moderately are employed or if the shell thickness of double emulsions is decreased to a few hundreds of nanometers.
乳液滴经常被用作容器，例如，在小体积中进行生化反应，或者在消耗最小样品体积的情况下进行高通量筛选分析。这些应用通常需要不允许试剂交换的液滴，以避免发生交叉污染。不幸的是，在许多情况下，即使试剂在周围相中溶解度低，乳液滴之间也会发生试剂交换，导致交叉污染。在这里，我们研究了使用水-油-水双乳液滴作为模型系统，亲水性试剂如何穿过油相进行传输的机制。值得注意的是，即使是大物体，包括 11000 个碱基对的双链环状 DNA，也可以穿过油壳进行传输。重要的是，这种试剂传输，在很大程度上是由在油水界面自发形成的含水液滴引起的，不仅限于双乳液，而且也发生在单乳液滴之间。我们证明，如果使用仅适度降低界面张力的适当表面活性剂，或者将双乳液的壳层厚度减小到几百纳米，则可以至少将不受控制的试剂传输降低一个数量级。
