Chen Xiaoxiao, Leary Thomas F, Maldarelli Charles
Department of Chemical Engineering, Benjamin Levich Institute, City College of the City University of New York , New York, New York 10031, USA.
Biomicrofluidics. 2017 Jan 4;11(1):014101. doi: 10.1063/1.4973247. eCollection 2017 Jan.
Arrays of probe molecules integrated into a microfluidic cell are utilized as analytical tools to screen the binding interactions of the displayed probes against a target molecule. These assay platforms are useful in enzyme or antibody discovery, clinical diagnostics, and biosensing, as their ultraminiaturized design allows for high sensitivity and reduced consumption of reagents and target. We study here a platform in which the probes are first grafted to microbeads which are then arrayed in the microfluidic cell by capture in a trapping course. We examine a course which consists of V-shaped, half-open enclosures, and study theoretically and experimentally target mass transfer to the surface probes. Target binding is a two step process of diffusion across streamlines which convect the target over the microbead surface, and kinetic conjugation to the surface probes. Finite element simulations are obtained to calculate the target surface concentration as a function of time. For slow convection, large diffusive gradients build around the microbead and the trap, decreasing the overall binding rate. For rapid convection, thin diffusion boundary layers develop along the microbead surface and within the trap, increasing the binding rate to the idealized limit of untrapped microbeads in a channel. Experiments are undertaken using the binding of a target, fluorescently labeled NeutrAvidin, to its binding partner biotin, on the microbead surface. With the simulations as a guide, we identify convective flow rates which minimize diffusion barriers so that the transport rate is only kinetically determined and measure the rate constant.
集成到微流控芯片中的探针分子阵列被用作分析工具，以筛选所展示的探针与目标分子之间的结合相互作用。这些检测平台在酶或抗体发现、临床诊断和生物传感方面很有用，因为其超小型化设计可实现高灵敏度，并减少试剂和目标物的消耗。我们在此研究一种平台，其中探针首先接枝到微珠上，然后通过捕获过程将微珠排列在微流控芯片中。我们研究了一个由V形半开放式外壳组成的过程，并从理论和实验上研究了目标物向表面探针的传质。目标物结合是一个两步过程，首先是跨流线扩散，使目标物在微珠表面对流，然后是与表面探针的动力学结合。通过有限元模拟来计算目标物表面浓度随时间的变化。对于缓慢对流，微珠和捕获区域周围会形成大的扩散梯度，从而降低整体结合速率。对于快速对流，微珠表面和捕获区域内会形成薄的扩散边界层，将结合速率提高到通道中未捕获微珠的理想极限。实验采用荧光标记的中性抗生物素蛋白作为目标物，研究其与微珠表面结合伴侣生物素的结合情况。以模拟为指导，我们确定了使扩散障碍最小化的对流流速，使得传输速率仅由动力学决定，并测量了速率常数。
