Corrigendum to “Deciphering electron-shuttling characteristics of epinephrine and dopamine for bioenergy extraction using microbial fuel cells” [Biochem. Eng. J. 148 (2019) 57–64](S1369703X19301366)(10.1016/j.bej.2019.04.018)

Thank you for publishing the article entitled “Deciphering electron-shuttling characteristics of epinephrine and dopamine for bioenergy extraction using microbial fuel cells (BEJ 148 (2019) 57–64). In this first-attempt study, we explored the electron-shuttling characteristics of epinephrine (EP) and dopamine (DA) as electron shuttles (ESs) to enhance power generation of microbial fuel cells (MFCs). However, we found that in this article a wrong formula in Origin software was misused to calculate the area of closed-loop curves in analysis of cyclic voltammetry (CV). As a result, the data presented in Table 1 and associated trends of serial cycle shown in Fig 2 were inaccurate. Therefore, we are writing to you to correct such mistakes for the data analysis in the above mentioned article. The needed corrections are described in detail below. We hope that the following corrections could serve for better and more accurate understanding of our published article. 1. The presentation of Section 3.1 paragraph 2 in the original paper should be corrected as follows: As indicated in Table 1, the closed-loop areas of CV scanning of DA, EP, GA, VC and VB were presented as electrochemical contents for comparison of their bioenergy potentials. As shown in Fig. 2, all these five substances clearly exhibited similar trends of electrochemical properties no matter what electrochemical status. The findings indicated that DA owned the largest closed-loop curve area (i.e., the richest electrochemical content) as compared to other substances. This might also suggested that DA owned the most significant oxidation-reduction potential properties among these five chemicals. According to repeated scan-course curves of closed-loop area for 5 test chemicals (Fig. 2), the oxidation-reduction characteristics asymptotically stabilized to steady state levels after 50 cycles. These all supported their strong characteristics of electrochemically reversible and stable ESs. This feasibility comparison might also suggest that antioxidants-abundant chemicals could be gradually oxidized via electrochemical treatment. However, likely due to adaptation of chemicals to achieve stable electrochemical responses, electrochemical potentials of ESs might be “reduced” initially and then asymptotically stabilized to reveal the nature of stable “electrochemical catalysis”. As a matter of fact, Chen et al. [16,17] confirmed that a simple phenolic compound 1,2-dihydroxylbenzene (catechol) owned electrochemically-reversible and stable characteristics as an ES. In addition, cyclic voltammograms of 100 scan cycles to simulate serial redox processes of catechol at neutral pH still clearly revealed reversible and stable reduction and oxidation peak currents, exhibiting strong electron-shuttling characteristics. If electron shuttles (e.g., dihydroxyl substituent(s)-bearing chemical such as catechol) could be reversible electrochemical catalysts with stable redox potential peaks in multiple cycles of CV scans, they could significantly stimulate bioelectricity-generating capabilities in MFCs. That is, ESs could still be stably remained intact about chemical structures and properties via repeated electron-releasing and withdrawing processes. Therefore, supplement of catecholamine hormones- dopamine and epinephrine as candidate ESs could stimulate bioelectricity-generating performance of MFCs for bioenergy extraction. 2. The presentation of Section 3.1 paragraph 3 Line 13–18 in the original paper should be corrected as follows: Thus, as Fig. 2 and Fig. 3 indicated, similar to VB, DA and EP even owned more significantly reversible and stable electrochemical characteristics for bioelectricity-generating expression in MFCs. To confirm whether such electron-shuttling characteristics could be adopted for bioenergy extraction, MFC modules were used for further confirmation afterwards in the Section 3.2. 3. The presentation of Section 3.2 paragraph 3 Line 1–11 in the original paper should be corrected as follows: As mentioned in Section 3.1, comparative CV profiles clearly showed the outstanding antioxidant activities of VC and GA. Their ratios of I_pa /I_pc of closed-loop cyclic voltammograms were relatively lower than those of ES species- DA, EP and VB. This seemed to imply that ESs (i.e., EP, DA and VB) even owned more significantly reversible and stable electrochemical characteristics for bioelectricity-generating expression in MFCs. 4. Table 1 and Fig. 2 in the original paper should be corrected as follows: Table 1 Comparison on closed-loop areas^* of CV profiles for dopamine (DA), epinephrine (EP), gallic acid (GA), vitamin C (VC) and vitamin B₂ (VB) at different scanning cycles (unit: μW) [Table presented] ^↑V_H, V_L denoted voltages of CV scan at +1.5 V and −1.5 V, respectively; and i_h, i_i denoted the highest and lowest electric current at specific scan voltage, respectively. [Figure presented] Fig. 2 Comparison on closed-loop areas of CV profiles at different scan cycle for dopamine (DA), epinephrine (EP), gallic acid (GA), vitamin C (VC) and vitamin B₂ (VB) The authors regret this corrigendum corrected the descriptions of original article dealing precisely what data were used. The authors would like to apologise for any inconvenience caused.