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The development of real-time online warning system for toxicity materials is important to ensure the safety of water supply. This study for the first time constructs luminescent bacteria (Vibrio fischeri) biofilm to deliver both electrical and optical real-time response for Cu(II) toxic shock in a bioelectrochemical system (BES) sensor. Compared to biocathode, bioanode was more suitable as sensitive elements. With three tested concentrations of Cu(II), i.e., 1 mg/L, 3 mg/L and 6 mg/L, electrical signals were raised. But optical signal failed to respond to the lowest concentration, suggesting that electrical signal then was produced by chemical reaction of Cu(II) on the electrode surface. For 3 mg/L and 6 mg/L Cu(II) shock, more rapid optical signals were observed than electrical signal, indicating that both the biofilm's surface and inner was affected. In addition, high concentration of Cu(II) toxic as 6 mg/L caused irreversible damage in the biosensor as there were great fluctuation in the recovery curve and large recovery ratio up to -10.39% for optical signal. These results provided a comparison between optical and electrical signals simultaneously produced by a biosensor and visual evidences for better understanding of the toxicity process in the biosensor. Image 1 • Luminescent bacteria biofilm was constructed as a sensing element. • Simultaneously production of photons and electrons by Vibrio fischeri biofilm. • Compatible Vibrio fischeri biofilm as bioanode rather than biocathode with biosensor. • Both optical and electrical signals respond to Cu2+ shock. [ABSTRACT FROM AUTHOR]