A single-layer structured microbial sensor for fast detection of biochemical oxygen demand

• B. subtilis are covalently bonded on gold electrode through MPA SAM for BOD detection.
• The direct immobilization of microorganisms reduces mass transfer resistance.
• The proposed microbial sensor can give a fast BOD response in 5 min.

In this paper, a novel biochemical oxygen demand (BOD) sensor based on a single layer of immobilized microorganisms on electrode for fast detection is investigated. Instead of the previous two-layer structure of oxygen permselective membrane and microorganism membrane, a single layer structure using electrodes as the support for microorganism immobilization has been studied. Amino functional groups on the surface of microorganisms have been bonded with carboxyl modified electrodes. Without extra supports for immobilization, mass transfer resistances are reduced, which facilitates fast current response. Bacillus subtilis cells with high biodegradation ability are obtained after 12 h cultivation. The immobilization process has been investigated by CV and EIS. B. subtilis cultivation time, response time and linear range have been optimized. The proposed sensor can reach equilibrium in 5 min which has the advantage for real-time BOD determination in the future. The linear range is 5–30 mg/l with correlation coefficient of 0.978 and limit of detection of 1.65 mg/l.

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