A novel glassy carbon electrode (GCE) modified with carbon-spheres has been fabricated through a simple casting procedure. The modified GCE displays high selectivity and excellent electrochemical catalytic activities towards dopamine (DA), serotonin (5-HT), and ascorbic acid (AA). In the co-existence system, the peak separations between AA and DA, DA and 5-HT, and AA and 5-HT are large up to 230, 180, and 410 mV, respectively. Differential pulse voltammetry (DPV) has been employed to simultaneously detect DA, 5-HT, and AA, and the linear calibration curves for DA, 5-HT, and AA are obtained in the range of 20.0–150.0 μM, 40.0–750.0 μM and 300.0–2,000.0 μM with detection limits (S/N = 3) of 2.0 μM, 0.7 μM and 0.6 μM, respectively. The proposed electrode has been applied to detect DA, 5-HT, and AA in real samples using standard addition method with satisfactory results.

The efficient immobilization of enzymes on favorable supporting materials to design enzyme electrodes endowed with specific catalysis performances such as deep oxidation of biofuels, and direct electron transfer (DET)-type bioelectrocatalysis is highly desired for fabricating enzymatic biofuel cells (BFCs). In this study, carbon nanodots (CNDs) have been used as the immobilizing matrixes and electron relays of enzymes to construct (NAD)-dependent dehydrogenase cascades-based bioanode for the deep oxidation of methanol and DET-type laccase-based biocathode for oxygen reduction to water. At the bioanode, multiplex enzymes including alcohol dehydrogenase, aldehyde dehydrogenase, and formate dehydrogenase are coimmobilized on CNDs electrode which is previously coated with in situ polymerized methylene blue as the electrocatalyst for oxidizing NADH to NAD. At the biocathode, fungal laccase is directly cast on CNDs and facilitated DET reaction is allowed. As a result, a novel membrane-less methanol/O BFC has been assembled and displays a high open-circuit voltage of 0.71(±0.02) V and a maximum power density of 68.7 (±0.4) μW cm. These investigated features imply that CNDs may act as new conductive architectures to elaborate enzyme electrodes for further bioelectrochemical applications.

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In this study, liquid-crystalline lipidic cubic phases (LCPs) formed by monoolein (MO) were used as hosting matrices to co-entrap enzymes and mediators to fabricate enzyme electrodes for biosensors and enzymatic biofuel cells (BFCs). An ethanol dehydrogenase (ADH)-based bioelectrode was fabricated by co-immobilizing ADH and electrocatalyst, toluidine blue (TB) into MO to form doped LCPs on glassy carbon substrate electrode. The prepared bioelectrode was used for ethanol sensing and bioanode of ethanol/air BFC. The constructed ethanol biosensor displays good linear concentration range from 0 to 15.6 mM with a detection limit of 0.09 mM and was applied for ethanol detection in human serum with satisfactory results. To construct an ethanol/air BFC, a biocathode for oxygen reduction was fabricated by co-immobilizing laccase and redox mediator, 2, 2 -azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) into MO to form doped LCPs on glassy carbon substrate electrode. The performances of the constructed ethanol/air BFC were characterized in buffer solution and red wine, respectively. The open circuit voltage (OCV) and maximum power density of the ethanol/air BFC are 0.53 V and 12.0 μWcm −2 at 0.36 V in buffer solution, and 0.42 V and 2.78 μW cm −2 at 0.26 V in red wine, respectively.