Label-free Lectin Impedimetric Biosensor Based on a Polyaniline/Graphene Nanocomposite for the Detection of Escherichia coli

This work reports a label-free impedimetric biosensor based on a polyaniline (PAM) and graphene (G) composite on a glassy carbon electrode (GCE) for the detection of Escherichia coli (E. coli) with lectin as the recognition molecule. The PANI/G nanocomposite was synthesized by in situ electrochemical oxidative polymerization of aniline onto G and Nafion. The effect of the polymerization on the electron performance of the sensing surface was checked. The results indicated that the heterogeneous electron transfer rate increased from 4.30 x 10(-4 c)m s 1 to 4.70 x 10(-4) cm s(-1) after the incorporation of PAM 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 demonstrated the recognition ability of the synthesis interface. The DH5 alpha E. coli bacteria strain was chosen as a model target. When the biosensor was incubated with the target under optimized experimental conditions, the electron transfer resistance (Ret) increased when the E. coli concentration increased from 5.0 x 10(1) cells/mL to 1.0 x 10(4) cells/mL. The detection limit for the biosensor was calculated to be 43 cells/mL based on a signal-to-noise ratio of 3. The biosensor was also challenged by incubation with two different bacteria without Con A binding sites, which showed negligible changes in the R-ef value. The hybrid PANI and G nanocomposite enables us to enhance the biosensor response and reproducibility without sacrificing the electrical conductivity, as found for the use of additives. The developed biosensor highlights a promising approach for the sensitive determination of other desired bacteria via incorporation with a nanocomposite.