Department of Materials Science and Engineering, National Chiao Tung University, 207, Engineering 1, 1001 University Road, Hsinchu, Taiwan.
Lab Chip. 2011 Aug 7;11(15):2500-8. doi: 10.1039/c1lc20142e. Epub 2011 Jun 10.
A water-core and oil-shell encapsulated droplet exhibits several advantages including enhanced fluidic manipulation, reduced biofouling, decreased evaporation, and simplified device packaging. However, obtaining the encapsulated droplet with an adjustable water-to-oil volume ratio and a further removable oil shell is not possible by reported techniques using manual pipetting or droplet splitting. We report a parallel-plate device capable of generation, encapsulation, rinsing, and emersion of water and/or oil droplets to achieve three major aims. The first aim of our experiments was to form encapsulated droplets by merging electrowetting-driven water droplets and dielectrophoresis-actuated oil droplets whose volumes were precisely controlled. 25 nL water droplets and 2.5 nL non-volatile silicone oil droplets with various viscosities (10, 100, and 1000 cSt) were individually created from their reservoirs to form encapsulated droplets holding different water-to-oil volume ratios of 10:1 and 2:1. Secondly, the driving voltages, evaporation rates, and biofouling of the precise encapsulated droplets were measured. Compared with the bare and immersed droplets, we found the encapsulated droplets (oil shells with lower viscosities and larger volumes) were driven at a smaller voltage or for a wider velocity range. In the dynamic evaporation tests, at a temperature of 20 ± 1 °C and relative humidity of 45 ± 3%, 10 cSt 10:1 and 2:1 encapsulated droplets were moved at the velocity of 0.25 mm s(-1) for 22 and 35 min until losing 16.6 and 17.5% water, respectively, while bare droplets followed the driving signal for only 6 min when 11.4% water was lost. Evaporation was further diminished at the rate of 0.04% min(-1) for a carefully positioned stationary encapsulated droplet. Biofouling of 5 μg ml(-1) FITC-BSA solution was found to be eliminated by the encapsulated droplet from the fluorescent images. The third aim of our research was to remove the oil shell by dissolving it in an on-chip rinsing reservoir containing hexane. After emersion from the rinsing reservoir, the bare droplet was restored as hexane rapidly evaporated. Removal of the oil shell would not only increase the evaporation of the core droplet when necessary, but also enhance the signal-to-noise ratio in the following detection steps.
水核油壳包裹液滴具有增强流体操控、减少生物污染、降低蒸发和简化器件封装等优点。然而，通过报道的使用手动移液或液滴分裂的技术，无法获得具有可调节水油体积比和进一步可移除油壳的包裹液滴。我们报告了一种能够产生、包裹、冲洗和浮出水滴和/或油滴的平行板器件，以实现三个主要目标。我们实验的第一个目的是通过合并由电润湿驱动的水液滴和由介电泳驱动的油液滴来形成包裹液滴，其体积可以精确控制。从各自的储液器中分别产生 25 nL 的水液滴和 2.5 nL 的非挥发性硅油液滴，其粘度分别为 10、100 和 1000 cSt，以形成具有 10:1 和 2:1 不同水油体积比的包裹液滴。其次，测量了精确包裹液滴的驱动电压、蒸发率和生物污染。与裸液滴和浸入液滴相比，我们发现包裹液滴（具有较低粘度和较大体积的油壳）在较小的电压或更宽的速度范围内被驱动。在动态蒸发测试中，在 20±1°C 和相对湿度 45±3%的条件下，10 cSt 的 10:1 和 2:1 包裹液滴以 0.25mm/s 的速度移动 22 和 35 min，分别损失 16.6%和 17.5%的水，而当损失 11.4%的水时，裸液滴仅跟随驱动信号 6 min。当小心定位的静止包裹液滴以 0.04%/min 的速率蒸发时，蒸发进一步减少。从荧光图像中发现，包裹液滴消除了 5μg/ml FITC-BSA 溶液的生物污染。我们研究的第三个目的是通过将其溶解在含有己烷的芯片冲洗储液器中，去除油壳。从冲洗储液器浮出后，由于己烷迅速蒸发，裸液滴得以恢复。去除油壳不仅在必要时会增加核心液滴的蒸发，而且还会提高后续检测步骤中的信噪比。
