Kim Do Hyoung, Oh Yoonbae, Shin Hojin, Blaha Charles D, Bennet Kevin E, Lee Kendall H, Kim In Young, Jang Dong Pyo
Department of Biomedical Engineering, Hanyang University, Seoul, Korea.
Department of Psychology, University of Memphis, Memphis, TN, USA.
J Electroanal Chem (Lausanne). 2014 Mar 15;717-718:157-164. doi: 10.1016/j.jelechem.2014.01.020.
The oxidation of dopamine (DA) around +0.6V potential in anodic sweep and its reduction around -0.1V in cathodic sweep at a relatively fast scanning rate (300 V/s or greater) have been used for identification of DA oxidation in fast-scan cyclic voltammetry (FSCV). However, compared to the oxidation peak of DA, the reduction peak has not been fully examined in analytical studies, although it has been used as one of the representative features to identify DA. In this study, the reduction process of DA was investigated using paired pulse voltammetry (PPV), which consists of two identical triangle-shaped waveforms, separated by a short interval at the holding potential. Especially, the discrepancies between the magnitude of the oxidation and reduction peaks of DA were investigated based on three factors: (1) the instant desorption of the DA oxidation product (dopamine-o-quinone: DOQ) after production, (2) the effect of the holding potential on the reduction process, and (3) the rate-limited reduction process of DA. For the first test, the triangle waveform FSCV experiment was performed on DA with various scanrates (from 400 to 1000 V/s) and durations of switching potentials of the triangle waveform (from 0.0 to 6.0 ms) in order to vary the duration between the applied oxidation potential at +0.6V and the reduction potential at -0.2V. As a result, the ratio of reduction over oxidation peak current response decreased as the duration became longer. To evaluate the effect of holding potentials during the reduction process, FSCV experiments were conducted with holding potential from 0.0V to -0.8V. We found that more negative holding potentials lead to larger amount of reduction process. For evaluation of the rate-limited reduction process of DA, PPV with a 1Hz repetition rate and various delays (2, 8, 20, 40 and 80ms) between the paired scans were utilized to determine how much reduction process occurred during the holding potential (-0.4V). These tests showed that relatively large amounts of DOQ are reduced to DA during the holding potential. The rate-limited reduction process was also confirmed with the increase of reduction in a lower pH environment. In addition to the mechanism of the reduction process of DA, we found that the differences between the responses of primary and secondary pulses in PPV were mainly dependent on the rate-limited reduction process during the holding potential. In conclusion, the reduction process may be one of the important factors to be considered in the kinetic analysis of DA and other electroactive species in brain tissue and in the design of new types of waveform in FSCV.
在快速扫描循环伏安法（FSCV）中，多巴胺（DA）在阳极扫描时约+0.6V电位处的氧化及其在阴极扫描时约-0.1V电位处的还原，且扫描速率相对较快（300V/s或更高），已被用于识别DA的氧化。然而，与DA的氧化峰相比，尽管其还原峰已被用作识别DA的代表性特征之一，但在分析研究中尚未得到充分研究。在本研究中，使用双脉冲伏安法（PPV）研究了DA的还原过程，PPV由两个相同的三角形波形组成，在保持电位处有一个短时间间隔。特别是，基于三个因素研究了DA氧化峰和还原峰大小之间的差异：（1）DA氧化产物（多巴胺邻醌：DOQ）产生后立即解吸；（2）保持电位对还原过程的影响；（3）DA的限速还原过程。对于第一次测试，对DA进行了三角形波形FSCV实验，扫描速率从400到1000V/s不等，三角形波形的切换电位持续时间从0.0到6.0ms不等，以改变+0.6V的施加氧化电位和-0.2V的还原电位之间的持续时间。结果，随着持续时间变长，还原峰电流响应与氧化峰电流响应的比值降低。为了评估还原过程中保持电位的影响，进行了保持电位从0.0V到-0.8V的FSCV实验。我们发现，更负的保持电位会导致更多的还原过程。为了评估DA的限速还原过程，使用了重复频率为1Hz且双扫描之间有不同延迟（2、8、20、40和80ms）的PPV，以确定在保持电位（-0.4V）期间发生了多少还原过程。这些测试表明，在保持电位期间，相对大量的DOQ被还原为DA。在较低pH环境中，随着还原量的增加，也证实了限速还原过程。除了DA还原过程的机制外，我们发现PPV中主脉冲和次脉冲响应之间的差异主要取决于保持电位期间的限速还原过程。总之，还原过程可能是脑组织中DA和其他电活性物质动力学分析以及FSCV新型波形设计中需要考虑的重要因素之一。
