Mavrogiannis Nicholas, Desmond Mitchell, Gagnon Zachary R
Department of Chemical and Biomolecular Engineering, Johns Hopkins University Baltimore, Baltimore, MD, USA.
Electrophoresis. 2015 Jul;36(13):1386-95. doi: 10.1002/elps.201400454. Epub 2015 Mar 12.
Traditional particle-based dielectrophoresis has been exploited to manipulate bubbles, particles, biomolecules, and cells. In this work, we investigate analytically and experimentally how to utilize Maxwell-Wagner polarization to initiate fluidic dielectrophoresis (fDEP) at electrically polarizable aqueous liquid-liquid interfaces. In fDEP, an AC electric field is applied across a liquid electrical interface created between two coflowing fluid streams with different electrical properties. When potentials as low as 2 volts are applied, we observe a frequency-dependent interfacial displacement that is dependent on the relative differences in the electrical conductivity (Δσ) and dielectric constant (Δɛ) between the two liquids. At low frequency this deflection is independent of dielectric constant, while at high frequency it is independent of electrical conductivity. At intermediate frequencies, we observe an fDEP cross-over frequency that is independent of applied voltage, sensitive to both fluid electrical properties, and where no displacement is observed. An analytical fDEP polarization model is presented that accurately predicts the liquid interfacial cross-over frequency, the dependence of interfacial displacement on liquid electrical conductivity and dielectric constant, and accurately scales the measured fDEP displacement data. The results show that miscible aqueous liquid interfaces are capable of polarizing under AC electric fields, and being precisely deflected in a direction and magnitude that is dependent on the applied electric field frequency.
传统的基于粒子的介电泳已被用于操控气泡、粒子、生物分子和细胞。在这项工作中，我们通过分析和实验研究了如何利用麦克斯韦-瓦格纳极化在可电极化的水相液-液界面引发流体介电泳（fDEP）。在fDEP中，交流电场施加于在具有不同电学性质的两股同向流动流体流之间形成的液体电界面上。当施加低至2伏的电势时，我们观察到一种与频率相关的界面位移，该位移取决于两种液体之间的电导率（Δσ）和介电常数（Δɛ）的相对差异。在低频时，这种偏转与介电常数无关，而在高频时，它与电导率无关。在中间频率时，我们观察到一个fDEP交叉频率，该频率与施加电压无关，对两种流体的电学性质都敏感，且在此频率下未观察到位移。提出了一个分析性的fDEP极化模型，该模型能准确预测液体界面交叉频率、界面位移对液体电导率和介电常数的依赖性，并能准确缩放测量的fDEP位移数据。结果表明，可混溶的水相液-液界面能够在交流电场下极化，并在取决于所施加电场频率的方向和幅度上被精确偏转。
