Jacobs Christopher B, Ivanov Ilia N, Nguyen Michael D, Zestos Alexander G, Venton B Jill
Department of Chemistry, University of Virginia , McCormick Road, Box 400319, Charlottesville, Virginia 22904-4319, United States.
Anal Chem. 2014 Jun 17;86(12):5721-7. doi: 10.1021/ac404050t. Epub 2014 May 28.
Fast-scan cyclic voltammetry (FSCV) can detect small changes in dopamine concentration; however, measurements are typically limited to scan repetition frequencies of 10 Hz. Dopamine oxidation at carbon-fiber microelectrodes (CFMEs) is dependent on dopamine adsorption, and increasing the frequency of FSCV scan repetitions decreases the oxidation current, because the time for adsorption is decreased. Using a commercially available carbon nanotube yarn, we characterized carbon nanotube yarn microelectrodes (CNTYMEs) for high-speed measurements with FSCV. For dopamine, CNTYMEs have a significantly lower ΔEp than CFMEs, a limit of detection of 10 ± 0.8 nM, and a linear response to 25 μM. Unlike CFMEs, the oxidation current of dopamine at CNTYMEs is independent of scan repetition frequency. At a scan rate of 2000 V/s, dopamine can be detected, without any loss in sensitivity, with scan frequencies up to 500 Hz, resulting in a temporal response that is four times faster than CFMEs. While the oxidation current is adsorption-controlled at both CFMEs and CNTYMEs, the adsorption and desorption kinetics differ. The desorption coefficient of dopamine-o-quinone (DOQ), the oxidation product of dopamine, is an order of magnitude larger than that of dopamine at CFMEs; thus, DOQ desorbs from the electrode and can diffuse away. At CNTYMEs, the rates of desorption for dopamine and dopamine-o-quinone are about equal, resulting in current that is independent of scan repetition frequency. Thus, there is no compromise with CNTYMEs: high sensitivity, high sampling frequency, and high temporal resolution can be achieved simultaneously. Therefore, CNTYMEs are attractive for high-speed applications.
快速扫描循环伏安法（FSCV）能够检测多巴胺浓度的微小变化；然而，测量通常限于10Hz的扫描重复频率。碳纤维微电极（CFME）上多巴胺的氧化取决于多巴胺的吸附，并且增加FSCV扫描重复频率会降低氧化电流，因为吸附时间减少了。我们使用市售的碳纳米管纱线，对用于FSCV高速测量的碳纳米管纱线微电极（CNTYME）进行了表征。对于多巴胺，CNTYME的ΔEp明显低于CFME，检测限为10±0.8 nM，对25μM呈线性响应。与CFME不同，CNTYME上多巴胺的氧化电流与扫描重复频率无关。在2000V/s的扫描速率下，多巴胺能够在高达500Hz的扫描频率下被检测到，且灵敏度没有任何损失，产生的时间响应比CFME快四倍。虽然CFME和CNTYME上的氧化电流均受吸附控制，但吸附和解吸动力学不同。多巴胺的氧化产物多巴胺邻醌（DOQ）的解吸系数比CFME上多巴胺的解吸系数大一个数量级；因此，DOQ从电极上解吸并可以扩散离开。在CNTYME上，多巴胺和多巴胺邻醌的解吸速率大致相等，导致电流与扫描重复频率无关。因此，CNTYME不存在折衷问题：可以同时实现高灵敏度、高采样频率和高时间分辨率。所以，CNTYME对于高速应用具有吸引力。
