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A highly sensitive whole cell based electrochemical biosensor was developed for catechol detection in this study. The carE gene of Sphingobium yanoikuyae XLDN2-5 encoding catechol 2,3-dioxygenase (C23O), a key enzyme in the biodegradation of aromatic compound, was cloned and over-expressed in Escherichia coli BL21 (E. coli BL21). Compared to Sphingobium yanoikuyae XLDN2-5, the recombinant E. coli BL21 over-expressed C23O exhibited higher catalytic activity towards catechol. Moreover, the whole cells provided a better environment for C23O to maintain its catalytic activity and stability compared with crude enzyme. The distinctive features of the recombinant E. coli BL21 over-expressed C23O made it an ideal bio-recognition element for the fabrication of a microbial biosensor. Additionally, nanoporous gold (NPG) with unique properties of structure and function was selected as a support to immobilized the recombinant E. coli BL21 over-expressed C23O. Based on the synergistic effect of C23O and NPG, the E. coli BL21-C23O/NPG/GCE bioelectrode showed a good linear response for catechol detection ranging from 1 μM to 500 μM with a high sensitivity of 332.24 μA mM -1 cm -2 and a low detection limit of 0.24 μM. Besides, the E. coli BL21-C23O/NPG/GCE bioelectrode exhibited strong anti-interference and good stability. For the detection of catechol in wastewater samples, the concentrations detected by the E. coli BL21-C23O/NPG/GCE bioelectrode were in good agreement with the standard concentrations that added in the wastewater samples, which make the E. coli BL21-C23O/NPG/GCE bioelectrode an ideal tool for reliable catechol detection., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Environmental pollution caused by sulfide compounds has become a major problem for public health. Hence, there is an urgent need to explore a sensitive, selective, and simple sulfide detection method for environmental monitoring and protection. Here, a novel microbial biosensor was developed using recombinant Escherichia coli BL21 (E. coli BL21) expressing sulfide:quinone oxidoreductase (SQR) for sulfide detection. As an important enzyme involved in the initial step of sulfide metabolism, SQR oxidizes sulfides to polysulfides and transfers electrons to the electron transport chain. Nanoporous gold (NPG) with its unique properties was selected for recombinant E. coli BL21 cells immobilization, and then glassy carbon electrode (GCE) was modified by the resulting E. coli/NPG biocomposites to construct an E. coli/NPG/GCE bioelectrode. Due to the catalytic oxidation properties of NPG for sulfide, the electrochemical reaction of the E. coli/NPG/GCE bioelectrode is attributed to the co-catalysis of SQR and NPG. For sulfide detection, the E. coli/NPG/GCE bioelectrode showed a good linear response ranging from 50μM to 5mM, with a high sensitivity of 18.35μAmM -1 cm -2 and a low detection limit of 2.55μM. The anti-interference ability of the E. coli/NPG/GCE bioelectrode is better than that of enzyme-based inhibitive biosensors. Further, the E. coli/NPG/GCE bioelectrode was successfully applied to the detection of sulfide in wastewater. These unique properties potentially make the E. coli/NPG/GCE bioelectrode an excellent choice for reliable sulfide detection., (Copyright © 2017 Elsevier B.V. All rights reserved.)