Electrochemical Measurement of Coenzyme Q10 Using Disposable Interdigitatad Array Electrode
Authors: Tsugawa Wakako , Watanabe Kentaro , Sode Koji 
Published: February 2020

Introduction
Coenzyme Q10 (CoQ10)　is an important component of the mitochondrial respiratory chain which exists as both oxidized form, CoQ10, and reduced form, CoQ10H2. CoQ10 is also known as an antioxidant in plasma, binding with lipoproteins during circulation. The antioxidative activity of CoQ10 depends on total CoQ10 concentration and percentage of CoQ10H2 in total CoQ10 in plasma. Since the ratio of CoQ10H2 is lower in patients with oxidative stress related diseases, it is considered to be an important marker for oxidative stress. At present, plasma CoQ10 and CoQ10H2 are usually determined by LC-electrochemical detector or LC-MS1,2) which are time-consuming, professional use and expensive analyzers. Considering the development of point of care (POCT) or on site sensor, simple, reliable, economical handy-type disposable test strip for CoQ10is favorable.
Interdigitated array electrodes (IDAE) have excellent performances, such as high current density and high sensitivity, due to their hemisphere diffusion and array configuration. In this study, we will present electrochemical measurement of CoQ10using disposable IDAE for POCT or on site sensor.
Methods
Various concentrations of CoQ10 or CoQ10H2solution were prepared in mixture of 2-propanol and ammonium acetate aqueous solution . Amperometric measurements were performed by single mode or dual mode using IDAE. All solutions were bubbled with Ar before use.
Results
We first measured the dual mode redox current of working electrode 1 (collector electrode) and working electrode 2 (generator electrode), which were applied oxidizing potential and reducing potential, respectively. When CoQ10 solution was applied to sensor strip, faradaic signal from both generator and collector electrodes were soon reached to steady-state value. The response current on both generator and collector electrodes showed positive correlation with CoQ10 concentration. When CoQ10 oxidized form was applied to the strip, oxidation current was observed, indicating that CoQ10oxidized form was reduced onto the generator electrode and diffused and re-oxidized onto the collector electrode, thus redox cycle occurred successfully. Next, we measured the single mode redox current of working electrode 1 by applying reduction potential or oxidation potential. Reduction current was observed for CoQ10 and oxidation current was observed for CoQ10H2 and both of them exhibit steady- state currents soon after the potential application. The response current detected on working electrode 1 when reduction potential was applied to CoQ10 solution, oxidized form, showed positive correlation with CoQ10 concentration. When the oxidation potential was applied to CoQ10H2 solution, positive correlation with CoQ10H2concentration was observed.
These results indicate that using IDAE, total CoQ10 concentration can be determined by dual mode amperometry and CoQ10 oxidized form or CoQ10H2can be determined by single mode amperometry
(1) P. H. Tang et al., Clin. Chem. 2, 47 (2001)
(2) J. Lagendijk, J. B. Ubbink, and W. J. H. Vermaak, J. Lipid Res. 1, 37 (1996)

Figure 1