Strutwolf Jörg, Scanlon Micheál D, Arrigan Damien W M
Tyndall National Institute, Lee Maltings, University College, Cork, Ireland.
Analyst. 2009 Jan;134(1):148-58. doi: 10.1039/b815256j. Epub 2008 Nov 20.
Miniaturised liquid/liquid interfaces provide benefits for bioanalytical detection with electrochemical methods. In this work, microporous silicon membranes which can be used for interface miniaturisation were characterized by simulations and experiments. The microporous membranes possessed hexagonal arrays of pores with radii between 10 and 25 microm, a pore depth of 100 microm and pore centre-to-centre separations between 99 and 986 microm. Cyclic voltammetry was used to monitor ion transfer across arrays of micro-interfaces between two immiscible electrolyte solutions (microITIES) formed at these membranes, with the organic phase present as an organogel. The results were compared to computational simulations taking into account mass transport by diffusion and encompassing diffusion to recessed interfaces and overlapped diffusion zones. The simulation and experimental data were both consistent with the situation where the location of the liquid/liquid (l/l) interface was on the aqueous side of the silicon membrane and the pores were filled with the organic phase. While the current for the forward potential scan (transfer of the ion from the aqueous phase to the organic phase) was strongly dependent on the location of the l/l interface, the current peak during the reverse scan (transfer of the ion from the organic phase to the aqueous phase) was influenced by the ratio of the transferring ion's diffusion coefficients in both phases. The diffusion coefficient of the transferring ion in the gelified organic phase was ca. nine times smaller than in the aqueous phase. Asymmetric cyclic voltammogram shapes were caused by the combined effect of non-symmetrical diffusion (spherical and linear) and by the inequality of the diffusion coefficient in both phases. Overlapping diffusion zones were responsible for the observation of current peaks instead of steady-state currents during the forward scan. The characterisation of the diffusion behaviour is an important requirement for application of these silicon membranes in electroanalytical chemistry.
小型化的液/液界面为采用电化学方法进行生物分析检测带来了诸多益处。在本研究中，通过模拟和实验对可用于界面小型化的微孔硅膜进行了表征。这些微孔膜具有六边形排列的孔，孔径在10至25微米之间，孔深为100微米，孔中心距在99至986微米之间。采用循环伏安法监测离子在由这些膜形成的两种不混溶电解质溶液（微ITIES）之间的微界面阵列上的转移情况，有机相以有机凝胶的形式存在。将结果与考虑扩散传质并涵盖向凹陷界面的扩散和重叠扩散区的计算模拟进行了比较。模拟和实验数据均与液/液（l/l）界面位于硅膜水相一侧且孔中充满有机相的情况一致。虽然正向电位扫描的电流（离子从水相转移到有机相）强烈依赖于l/l界面的位置，但反向扫描期间的电流峰（离子从有机相转移到水相）受转移离子在两相中扩散系数之比的影响。转移离子在凝胶化有机相中的扩散系数约为水相中的九分之一。不对称的循环伏安图形状是由非对称扩散（球形和线性）的综合效应以及两相中扩散系数的不等性造成的。重叠扩散区导致在正向扫描期间观察到电流峰而非稳态电流。扩散行为的表征是这些硅膜在电分析化学中应用的一项重要要求。
