Facile preparation of disposable immunosensor for Shigella flexneri based on multi-wall carbon nanotubes/chitosan composite

Based on multi-wall carbon nanotubes (MWCNT)/chitosan/horseradish peroxidase labeled antibodies to Shigella flexneri (HRP-anti-S. flexneri) biocomposite film on a screen-printed electrode (SPE) surface, a disposable immunosensor has been developed for the rapid detection of S. flexneri. The HRP-anti-S. flexneri can be entrapped into MWCNT/chitosan composite matrix without other cross-linking agent. Thionine and H2O2 were used as the mediator and substrate, respectively. The surface morphologies of modified films were characterized by atomic force microscope (AFM). Cyclic voltammery (CV) was carried out to characterize the electrochemical properties of the immobilization of materials on the electrode surface and quantified S. flexneri. Due to the strong electrocatalytic properties of MWCNT and HRP toward H2O2, the response signal was significantly amplified. S. flexneri could be detected by the decrease of the reduction peak current before and after immunoreaction. Under optimal conditions, S. flexneri could be detected in the range of 104 to 1010 cfu mL−1, with a detection limit of 2.3 × 103 cfu mL−1 (S/N = 3). Furthermore, the proposed immunosensor exhibited a satisfactory specificity, reproducibility, stability and accuracy, indicating that the proposed immunosensor has potential application for a facile, rapid and harmless immunoassay.