Optical impedance spectroscopy with single-mode electro-active-integrated optical waveguides.
Optical impedance spectroscopy with single-mode electro-active-integrated optical waveguides.
复制标题
具有单模电活性集成光波导的光阻抗谱。
DOI：
10.1021/ac4030736
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发表时间：
2014
影响因子：
7.4
通讯作者：
Mendes,SergioB
中科院分区：
文献类型：
--
作者：
Han,Xue;Mendes,SergioB
开发了一种基于单模电活性集成光波导（EA-IOW）的光阻抗谱（OIS）技术来研究氧化还原吸附物的电子转移过程。使用高度灵敏的单模 EA-IOW 器件来光学跟踪源自细胞色素亚单层的时间依赖性法拉第电流，该电流由在多个直流偏置电势和多个频率下的电势谐波调制驱动，进行氧化还原交换。为了正确地从交流调制光信号中检索法拉第电流密度，我们在这里引入了一种数学形式，它（i）解释了电势调制期间 EA-IOW 器件的光学基线中总是发生的内在变化，以及（ii）为电化学参数提供了准确的结果。我们能够根据工作电极中的直流偏置电势以光学方式重建法拉第电流密度分布，识别形式电势，并确定电子转移过程的能量宽度。此外，通过将光学重建的法拉第信号与整个电化学电池的阻抗和双电层的电容的简单电测量相结合，我们能够确定与吸附的蛋白质组装体的氧化还原反应相关的时间常数。对于直接固定在氧化铟锡 (ITO) 表面的细胞色素，我们测得反应速率常数为 26.5 s–1。最后，我们计算了与电子转移过程相关的电荷转移电阻和赝电容，并表明蛋白质亚单层氧化还原反应的频率依赖性符合预期的 RC 串联导纳图的电学等效关系。最重要的是，我们在这里展示了具有单模式 EA-IOW 的 OIS 提供了强大的分析信号，即使对于氧化还原过程中涉及的物质的小表面密度（例如，fmol/cm2，完整蛋白质单层的 0.1%），也可以轻松监测这些信号。这种实验方法与此处描述的分析形式相结合，为电化学分析带来了额外的灵敏度、准确性和简单性，并有望成为氧化还原过程研究的有用工具。
An optical impedance spectroscopy (OIS) technique based on a single-mode electro-active-integrated optical waveguide (EA-IOW) was developed to investigate electron-transfer processes of redox adsorbates. A highly sensitive single-mode EA-IOW device was used to optically follow the time-dependent faradaic current originated from a submonolayer of cytochromecundergoing redox exchanges driven by a harmonic modulation of the electric potential at several dc bias potentials and at several frequencies. To properly retrieve the faradaic current density from the ac-modulated optical signal, we introduce here a mathematical formalism that (i) accounts for intrinsic changes that invariably occur in the optical baseline of the EA-IOW device during potential modulation and (ii) provides accurate results for the electro-chemical parameters. We are able to optically reconstruct the faradaic current density profile against the dc bias potential in the working electrode, identify the formal potential, and determine the energy-width of the electron-transfer process. In addition, by combining the optically reconstructed faradaic signal with simple electrical measurements of impedance across the whole electrochemical cell and the capacitance of the electric double-layer, we are able to determine the time-constant connected to the redox reaction of the adsorbed protein assembly. For cytochromecdirectly immobilized onto the indium tin oxide (ITO) surface, we measured a reaction rate constant of 26.5 s–1. Finally, we calculate the charge-transfer resistance and pseudocapacitance associated with the electron-transfer process and show that the frequency dependence of the redox reaction of the protein submonolayer follows as expected the electrical equivalent of an RC-series admittance diagram. Above all, we show here that OIS with single-mode EA-IOW’s provide strong analytical signals that can be readily monitored even for small surface-densities of species involved in the redox process (e.g., fmol/cm2, 0.1% of a full protein monolayer). This experimental approach, when combined with the analytical formalism described here, brings additional sensitivity, accuracy, and simplicity to electro-chemical analysis and is expected to become a useful tool in investigations of redox processes.