Department of Chemical Engineering, Michigan Technological University, Houghton, Michigan 49931, United States.
Mechanical and Aerospace Engineering Department, Case Western Reserve University, Cleveland, Ohio 44106, United States.
Langmuir. 2022 May 17;38(19):5977-5986. doi: 10.1021/acs.langmuir.2c00013. Epub 2022 May 4.
The ability to generate stable, spatiotemporally controllable concentration gradients is critical for both electrokinetic and biological applications such as directional wetting and chemotaxis. Electrochemical techniques for generating solution and surface gradients display benefits such as simplicity, controllability, and compatibility with automation. Here, we present an exploratory study for generating microscale spatiotemporally controllable gradients using a reaction-free electrokinetic technique in a microfluidic environment. Methanol solutions with ionic fluorescein isothiocyanate (FITC) molecules were used as an illustrative electrolyte. Spatially nonuniform alternating current (AC) electric fields were applied using hafnium dioxide (HfO)-coated Ti/Au electrode pairs. Results from spatial and temporal analyses along with control experiments suggest that the FITC ion concentration gradient in bulk fluid (over 50 μm from the electrode) was established due to spatial variation of electric field density, and was independent of electrochemical reactions at the electrode surface. The established ion concentration gradients depended on both amplitudes and frequencies of the oscillating AC electric field. Overall, this work reports a novel approach for generating stable and spatiotemporally tunable gradients in a microfluidic chamber using a reaction-free electrochemical methodology.
生成稳定的、时空可控的浓度梯度的能力对于电动和生物应用都至关重要，例如定向润湿和趋化性。电化学技术用于产生溶液和表面梯度具有简单、可控和与自动化兼容等优点。在这里，我们提出了一项在微流环境中使用无反应电动技术生成微尺度时空可控梯度的探索性研究。含有离子荧光素异硫氰酸酯（FITC）分子的甲醇溶液被用作说明性电解质。使用二氧化铪（HfO）涂层的 Ti/Au 电极对施加空间不均匀的交流（AC）电场。空间和时间分析以及对照实验的结果表明，由于电场密度的空间变化，在 bulk 流体（距电极 50 μm 以上）中建立了 FITC 离子浓度梯度，并且与电极表面的电化学反应无关。建立的离子浓度梯度取决于振荡交流电场的幅度和频率。总的来说，这项工作报道了一种使用无反应电化学方法在微流腔中生成稳定和时空可调梯度的新方法。
