Zhao Yuliang, Lai Hok Sum Sam, Zhang Guanglie, Lee Gwo-Bin, Li Wen Jung
Dept. of Mechanical and Biomedical Engineering, City University of Hong Kong, Hong Kong.
Lab Chip. 2014 Nov 21;14(22):4426-34. doi: 10.1039/c4lc00795f.
The density of a single cell is a fundamental property of cells. Cells in the same cycle phase have similar volume, but the differences in their mass and density could elucidate each cell's physiological state. Here we report a novel technique to rapidly measure the density and mass of a single cell using an optically induced electrokinetics (OEK) microfluidic platform. Presently, single cellular mass and density measurement devices require a complicated fabrication process and their output is not scalable, i.e., it is extremely difficult to measure the mass and density of a large quantity of cells rapidly. The technique reported here operates on a principle combining sedimentation theory, computer vision, and microparticle manipulation techniques in an OEK microfluidic platform. We will show in this paper that this technique enables the measurement of single-cell volume, density, and mass rapidly and accurately in a repeatable manner. The technique is also scalable - it allows simultaneous measurement of volume, density, and mass of multiple cells. Essentially, a simple time-controlled projected light pattern is used to illuminate the selected area on the OEK microfluidic chip that contains cells to lift the cells to a particular height above the chip's surface. Then, the cells are allowed to "free fall" to the chip's surface, with competing buoyancy, gravitational, and fluidic drag forces acting on the cells. By using a computer vision algorithm to accurately track the motion of the cells and then relate the cells' motion trajectory to sedimentation theory, the volume, mass, and density of each cell can be rapidly determined. A theoretical model of micro-sized spheres settling towards an infinite plane in a microfluidic environment is first derived and validated experimentally using standard micropolystyrene beads to demonstrate the viability and accuracy of this new technique. Next, we show that the yeast cell volume, mass, and density could be rapidly determined using this technology, with results comparable to those using the existing method suspended microchannel resonator.
单细胞的密度是细胞的一项基本属性。处于相同周期阶段的细胞具有相似的体积，但其质量和密度的差异能够阐明每个细胞的生理状态。在此，我们报告一种利用光诱导电动力学（OEK）微流控平台快速测量单细胞密度和质量的新技术。目前，单细胞质量和密度测量设备需要复杂的制造工艺，且其输出不可扩展，即极难快速测量大量细胞的质量和密度。本文所报告的技术基于一种将沉降理论、计算机视觉和微粒操纵技术相结合的原理，在OEK微流控平台上运行。我们将在本文中表明，该技术能够以可重复的方式快速、准确地测量单细胞的体积、密度和质量。该技术还具有可扩展性——它允许同时测量多个细胞的体积、密度和质量。本质上，一种简单的时间控制投影光图案用于照亮OEK微流控芯片上包含细胞的选定区域，将细胞提升至芯片表面上方的特定高度。然后，让细胞“自由下落”至芯片表面，此时细胞受到浮力、重力和流体阻力的共同作用。通过使用计算机视觉算法精确跟踪细胞的运动，然后将细胞的运动轨迹与沉降理论相关联，每个细胞的体积、质量和密度就能快速确定。首先推导了微流体环境中微小球体朝向无限平面沉降的理论模型，并使用标准微聚苯乙烯珠进行了实验验证，以证明这项新技术的可行性和准确性。接下来，我们表明利用这项技术能够快速测定酵母细胞的体积、质量和密度，其结果与使用现有悬浮微通道谐振器方法得到的结果相当。
