Department of Chemical and Biological Engineering, University of Wisconsin-Madison , 1415 Engineering Drive, Madison, Wisconsin 53706, United States.
Anal Chem. 2013 Nov 5;85(21):10296-303. doi: 10.1021/ac4021193. Epub 2013 Oct 22.
We report the use of flow cytometry to identify the internal ordering (director configurations) of micrometer-sized droplets of thermotropic liquid crystals (LCs) dispersed in aqueous solutions of adsorbates (surfactants and phospholipids). We reveal that changes in the configurations of the LC droplets induced by the adsorbates generate distinct changes in light scattering plots (side versus forward scattering). Specifically, when compared to bipolar droplets, radial droplets generate a narrower distribution of side scattering intensities (SSC, large angle light scattering) for a given intensity of forward scattering (FSC, small angle light scattering). This difference is shown to arise from the rotational symmetry of a radial LC droplet which is absent for the bipolar configuration of the LC droplet. In addition, the scatter plots for radial droplets possess a characteristic "S-shape", with two or more SSC intensities observed for each intensity of FSC. The origin of the experimentally observed S-shape is investigated via calculation of form factors and established to be due to size-dependent interference effects that differ for the forward and side scattered light. Finally, by analyzing emulsions composed of mixtures of bipolar and radial droplets at rates of up to 10,000 droplets per second, we demonstrate that flow cytometry permits precise determination of the percentage of radial droplets within the mixture with a coefficient of determination of 0.98 (as validated by optical microscopy). Overall, the results presented in this paper demonstrate that flow cytometry provides a promising approach for high throughput quantification of the internal configurations of LC emulsion microdroplets. Because large numbers of droplets can be characterized, it enables statistically robust analyses of LC droplets. The methodology also appears promising for quantification of chemical and biological assays based on adsorbate-induced ordering transitions within LC droplets.
我们报告了使用流式细胞术来识别分散在吸附剂（表面活性剂和磷脂）水溶液中的热致液晶（LC）微滴的内部有序性（指向配置）。我们揭示了吸附剂引起的 LC 液滴配置的变化会导致光散射图（侧向与前向散射）产生明显变化。具体来说，与双极液滴相比，径向液滴在给定的前向散射（小角光散射）强度下产生更窄的侧向散射强度（SSC，大角度光散射）分布。这种差异源于径向 LC 液滴的旋转对称性，而双极 LC 液滴的配置则不存在这种对称性。此外，径向液滴的散射图具有特征的“S 形”，对于每个 FSC 强度观察到两个或更多个 SSC 强度。通过计算形态因子并确定其原因是前向和侧向散射光的尺寸相关干涉效应不同，对实验观察到的 S 形的起源进行了研究。最后，通过以高达每秒 10,000 个液滴的速率分析由双极和径向液滴混合物组成的乳液，我们证明了流式细胞术可以精确确定混合物中径向液滴的百分比，其决定系数为 0.98（通过光学显微镜验证）。总体而言，本文介绍的结果表明，流式细胞术为高通量定量 LC 乳液微滴的内部配置提供了一种有前途的方法。由于可以对大量液滴进行表征，因此可以对 LC 液滴进行统计上可靠的分析。该方法似乎也有望用于基于 LC 液滴中吸附剂诱导的有序转变的化学和生物学测定的定量。
