Department of Mechanical and Aerospace Engineering, The Ohio State University , Columbus, Ohio 43210, United States.
Anal Chem. 2017 Feb 7;89(3):1593-1601. doi: 10.1021/acs.analchem.6b03653. Epub 2017 Jan 6.
Surface charge governs nanoscale aqueous electrolyte transport, both in engineered analytical systems and in biological entities such as ion channels and ion pumps as a function of ion type and concentration. Embedded electrodes in a nanofluidic channel, isolated from the fluid in the channel by a dielectric layer, act as active, tunable gates to systematically modify local surface charge density at the interface between the nanochannel surface and the aqueous electrolyte solution, causing significant changes in measured nanochannel conductance. A systematic comparison of transport of monovalent electrolytes [potassium chloride (KCl), sodium chloride (NaCl)], 2:1 electrolytes [magnesium chloride (MgCl), calcium chloride (CaCl)], and electrolyte mixtures (KCl + CaCl) through a gated nanofluidic device was performed. Ion-surface interactions between divalent Ca and Mg ions and the nanochannel walls reduced the native surface charge density by up to ∼4-5 times compared to the monovalent cations. In electrolyte mixtures, Ca was the dominating cation with nanochannel conductance independent of KCl concentration. Systematic changes in local electrostatic surface state induced by the gate electrode are impacted by the divalent cation-surface interactions, limiting modulation of the local surface potential by the gate electrode and resulting in cation dependent nanoscale ion transport as seen through conductance measurements and numerical models.
表面电荷控制着纳米尺度水相电解质的传输，无论是在工程分析系统中，还是在离子通道和离子泵等生物实体中，这都取决于离子的类型和浓度。在纳米流道中嵌入的电极与流道中的流体通过介电层隔离，作为主动可调的门，系统地改变纳米通道表面和水相电解质溶液之间界面处的局部表面电荷密度，导致测量得到的纳米通道电导发生显著变化。通过一个带门控的纳米流道装置，对单价电解质[氯化钾（KCl）、氯化钠（NaCl）]、2:1 电解质[氯化镁（MgCl）、氯化钙（CaCl）]和电解质混合物（KCl+CaCl）的传输进行了系统比较。与单价阳离子相比，二价 Ca 和 Mg 离子与纳米通道壁之间的离子-表面相互作用将本征表面电荷密度降低了约 4-5 倍。在电解质混合物中，Ca 是主要的阳离子，纳米通道电导与 KCl 浓度无关。门电极引起的局部静电表面状态的系统变化受到二价阳离子-表面相互作用的影响，限制了门电极对局部表面电势的调制，导致通过电导测量和数值模型观察到的阳离子依赖的纳米尺度离子传输。
