Two-dimensional (2D) microdroplet arrays with indexed sample concentration gradients have been receiving considerable attention for high-throughput biological and medical analyses. However, the preparation of such an array by conventional methods mandates precise pipetting and/or pumping. In this paper, we introduce a method to spontaneously generate 2D-arrayed aqueous droplets using a well array, for which coarse pipetting is sufficient. The wells are connected in rows and columns via narrow channels. Aqueous solutions impregnated in the well array are split into droplets in every single well as a subsequently introduced immiscible solvent self-propagates and divides the solution at the channels. A concentration gradient of the samples can be formed across the connected solution in the well array; once droplets are generated, each droplet possesses a different sample concentration depending on its position in the array. We experimentally determined the optimal well dimensions and solvent species to obtain a high yield of droplet generation. We next demonstrated a 2D droplet array with a two-sample concentration gradient. Finally, the applicability of the system was demonstrated through a cell viability assay using a sample that induced apoptosis. We believe the proposed method contributes to simplification and miniaturization of the system to generate droplet arrays and thus is applicable to biological and medical analysis.

中文翻译：

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利用油水不混溶性和置换作用自动生成二维液滴阵列†

具有索引的样品浓度梯度的二维（2D）微滴阵列已受到高通量生物学和医学分析的广泛关注。然而，通过常规方法制备这种阵列要求精确的移液和/或泵送。在本文中，我们介绍了一种使用井阵列自发生成2D阵列水液滴的方法，对于该液滴，粗略的移液就足够了。这些孔通过狭窄的渠道。浸渍在孔阵列中的水溶液在每个孔中均分成小滴，随后引入的不溶混的溶剂会自我繁殖，并在通道处分配溶液。样品的浓度梯度可以在孔阵列中连接的所有溶液上形成。一旦产生液滴，取决于其在阵列中的位置，每个液滴将具有不同的样品浓度。我们通过实验确定了最佳的孔尺寸和溶剂种类，以获得高产的液滴。接下来，我们演示了具有两个样本浓度梯度的2D液滴阵列。最后，该系统的适用性通过使用诱导凋亡的样品的细胞存活力测定法进行了证明。