A novel biosensor for zinc detection based on microbial fuel cell system

Microbial fuel cell (MFC) biosensors are self-sustainable device for monitoring of various substrates; however, for heavy metals detection are still scarce. In this study, E. coli BL21 was engineered to express the zntR, ribB, and oprF genes with P-zntA promoter, which could sense zinc (Zn2+) for riboflavin and porin production. The engineered strain produced high levels of riboflavin (2.4-3.6 mu M) and improved cell membrane permeability, with a positive correlation of Zn2+ (0-400 mu M). The strain was then employed in MFC biosensor under the following operational parameters: external resistance 1000 Omega, pH 9, and temperature 37 degrees C for Zn2+ sensing. The maximum voltages (160, 183, 260, 292, and 342 mV) of the constructed MFC biosensor have a linear relationship with Zn2+ concentrations (0, 100, 200, 300, and 400 mu M, respectively) (R-2 = 0.9777). An Android App was developed for the biosensor system that could sense Zn2+ in real-time and in situ. The biosensor was applied to wastewater with different Zn2+ concentrations and the results showed that the detection range for Zn2+ was 20-100 mu M, which covers common Zn2+ safety standards. The results obtained with developed MFC biosensor were comparable to conventional methods such as colorimetric, flame atomic absorption spectroscopy (FAAS), and inductively coupled plasma optical emission spectroscopy (ICP-OES). In summary, MFC biosensor with biosynthetic strain is an efficient and affordable system for real-time monitoring and sensing of heavy metals.