Abstract
We have developed a novel mediated biochemical oxygen demand (BOD) biosensor based on immobilized Bacillus subtilis (B. subtilis) on three-dimensional (3D) porous graphene-polypyrrole (rGO-PPy) composite. The 3D porous rGO-PPy composite was prepared using hydrothermal method following with electropolymerization. Then the 3D porous rGO-PPy composite was used as a support for immobilizing negatively charged B. subtilis denoted as rGO-PPy-B through coordination and electrostatic interaction. Further, the prepared rGO-PPy-B was used as a microbial biofilm for establishing a mediated BOD biosensor with ferricyanide as an electronic acceptor. The indirect determination of BOD was performed by electrochemical measuring ferrocyanide generated from a reduced ferricyanide mediator using interdigited ultramicroelectrode array (IUDA) as the working electrode. The experimental results suggested a good linear relationship between the amperometric responses and BOD standard concentrations from 4 to 60 mg/L, with a limit detection of 1.8 mg/L (S/N ≥ 3). The electrochemical measurement of real water samples showed a good agreement with the conventional BOD5 method, and the good anti-interference as well as the long-term stability were well demonstrated, indicating that the proposed mediated BOD biosensor in this study holds a potential practical application of real water monitoring.
Highlights
To date, the problem of organic pollution in river and lake water has been more and more serious in some countries [1]
We developed a mediated biochemical oxygen demand (BOD) biosensor for BOD measurement in low concentration
The major innovation is that 3D porous rGO-PPy composite was synthesized for B. subtilis immobilization
Summary
The problem of organic pollution in river and lake water has been more and more serious in some countries [1]. The European Union proposed surface water quality standard on BOD concentration range of the class I~V being 3 mg/L~7 mg/L [3]. 3D porous graphene-polypyrrole (rGO-PPy) composite was synthesized by two steps for B. subtilis immobilization. Pyrrole was added in graphene oxide (GO) dispersion in order to hinder the assembly of rGO (reduced graphene oxide, named graphene) sheets and adjust the pore size of resultant rGO hydrogels, and the obtained graphene can coordinate with the groups of amion and hydroxyl on B. subtilis. The immobilized B. subtilis on rGO-PPy composite was denoted as rGO-PPy-B, which was placed into a small bioreactor as a microbial biofilm for biocatalytic degradation of organic substances in water sample. The electrochemical characteristics and high performance of the resultant mediated BOD biosensor with respect to linear range, the detection limit, reproducibility, selectivity and stability was investigated in detail
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