Chen Delai, Du Wenbin, Ismagilov Rustem F
Department of Chemistry and Institute for Biophysical Dynamics, The University of Chicago, 929 East 57th Street, Chicago, IL 60637, USA.
New J Phys. 2009;11(31):75017. doi: 10.1088/1367-2630/11/7/075017.
This paper describes experiments for characterizing mass transfer at the hydrophilic surface of the substrate in a chemistrode. The chemistrode uses microfluidic plugs to deliver pulses of chemicals to a substrate with high temporal resolution, which requires efficient mass transfer between the wetting layer and the hydrophilic surface of the substrate. Here, total internal reflection fluorescence microscopy (TIRFM) was used to image the hydrophilic surface of the substrate as plugs were made to flow over it. The surface of the substrate was rapidly saturated with a fluorescent dye as the fluroesecent plugs passed over the substrate, confirming effective mass transfer between the wetting layer and the surface of the substrate. The dynamics of saturation are consistent from cycle to cycle, indicating that the chemistrode can stimulate surfaces with high reproducibility. The number of plugs required to reach 90% saturation of the hydrophilic surface of the substrate, ϕ(90%), only weakly depended on experimental conditions (the Péclet number or the capillary number). Furthermore, over a wide range of operating conditions, ϕ(90%) was less than 4. These results are useful for improving the chemistrode and for understanding other phenomena that involve diffusional transfer in multiphase or recirculating flows near surfaces.
本文描述了用于表征化学传感器中底物亲水性表面传质特性的实验。该化学传感器利用微流体塞以高时间分辨率将化学物质脉冲输送到底物上，这需要在湿润层和底物亲水性表面之间进行高效传质。在此，当微流体塞在底物上流动时，使用全内反射荧光显微镜（TIRFM）对底物的亲水性表面进行成像。当荧光微流体塞经过底物时，底物表面迅速被荧光染料饱和，证实了在湿润层和底物表面之间存在有效的传质。饱和动力学在各个循环中保持一致，表明该化学传感器能够以高重现性刺激表面。使底物亲水性表面达到90%饱和所需的微流体塞数量ϕ(90%)仅微弱地依赖于实验条件（佩克莱数或毛细管数）。此外，在广泛的操作条件范围内，ϕ(90%)小于4。这些结果对于改进化学传感器以及理解其他涉及表面附近多相或循环流中扩散传递的现象很有用。
