Department of Biomedical Engineering, University of Wisconsin-Madison, Madison, WI 53705, USA.
Department of Medicine, Wisconsin Institutes for Medical Research, University of Wisconsin-Madison, Madison, WI 53705, USA.
Lab Chip. 2022 Jan 18;22(2):286-295. doi: 10.1039/d1lc00906k.
The addition of reagents for assays in digital microfluidic (DMF) systems is traditionally done by merging of droplets containing different analytes or reagents in solution. However, this process significantly increases droplet volume after each step, resulting in dilution of the analyte and reagents. Here, we report a new technique for performing reagent additions to aqueous droplets without significantly increasing the droplet's volume: volume-less reagent delivery (VRD). VRD is enabled by a physical phenomenon we call "exclusive liquid repellency" (ELR), which describes an aqueous/oil/solid 3-phase system where the aqueous phase can be fully repelled from a solid phase (contact angle ∼180°). When performing VRD, a reagent of interest in solution is deposited onto the ELR solid surface and allowed to dry. The ELR surface containing the dried reagent is then immersed under oil, followed by introduction of an aqueous droplet. By dragging the aqueous droplet over the spot of dried reagent using paramagnetic particles or a physical sliding wall, the droplet can then recover and reconstitute the reagent with negligible increase in its total volume, returning the ELR surface to its initial liquid repellent state in the process. We demonstrate that VRD can be performed across a wide range of reagent types including sugars, proteins (antibodies), nucleic acids (DNA), antibiotics, and even complex enzyme/substrate/buffer "kit" mixtures. We believe VRD is a flexible and powerful technique which can further the development of self-contained, multi-step assays in DMF and other microfluidic systems.
在数字微流控（DMF）系统中添加试剂的传统方法是通过合并含有不同分析物或试剂的液滴来实现的。然而，这一过程在每一步后都会显著增加液滴的体积，导致分析物和试剂的稀释。在这里，我们报告了一种在不显著增加液滴体积的情况下向水性液滴中进行试剂添加的新技术：无体积试剂输送（VRD）。VRD 通过我们称之为“排他性液体排斥”（ELR）的物理现象来实现，它描述了一个水/油/固三相系统，其中水相可以完全被固体相排斥（接触角约 180°）。在进行 VRD 时，将感兴趣的试剂溶液沉积在 ELR 固体表面上并使其干燥。然后将含有干燥试剂的 ELR 表面浸入油中，再引入水性液滴。通过使用顺磁性颗粒或物理滑动壁将水性液滴拖过干燥试剂的斑点，可以使液滴恢复并重新形成试剂，而其总体积几乎没有增加，在此过程中，ELR 表面恢复到初始的液体排斥状态。我们证明，VRD 可以在广泛的试剂类型中进行，包括糖、蛋白质（抗体）、核酸（DNA）、抗生素，甚至是复杂的酶/底物/缓冲液“试剂盒”混合物。我们相信，VRD 是一种灵活而强大的技术，可以进一步发展 DMF 和其他微流控系统中的独立、多步骤分析。
