This work reports a label-free impedimetric biosensor based on a polyaniline (PANI) and graphene (G)composite on a glassy carbon electrode (GCE) for the detection of Escherichia coli (E. coli) with lectinas the recognition molecule. The PANI/G nanocomposite was synthesized by in situ electrochemicaloxidative polymerization of aniline onto G and Nafion. The effect of the polymerization on theelectron performance of the sensing surface was checked. The results indicated that the heterogeneouselectron transfer rate increased from 4.30 × 10?4cm s?1 to 4.70 × 10?4cm s?1after the incorporation ofPANI onto the G/Nafion/GCE with ferrous/ferric as the redox probe. The lectin of Concanavalin A(Con A) was used to recognize the carbohydrate moiety on the surface of E. coli, which demonstratedthe recognition ability of the synthesis interface. The DH5α E. coli bacteria strain was chosen as amodel target. When the biosensor was incubated with the target under optimized experimentalconditions, the electron transfer resistance (Ret) increased when the E. coli concentration increasedfrom 5.0 × 101cells/mL to 1.0 × 104cells/mL. The detection limit for the biosensor was calculated tobe 43 cells/mL based on a signal-to-noise ratio of 3. The biosensor was also challenged by incubationwith two different bacteria without Con A binding sites, which showed negligible changes in the Retvalue. The hybrid PANI and G nanocomposite enables us to enhance the biosensor response andreproducibility without sacrificing the electrical conductivity, as found for the use of additives. Thedeveloped biosensor highlights a promising approach for the sensitive determination of other desiredbacteria via incorporation with a nanocomposite..
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