Layer-by-layer electrochemical biosensor with aptamer-appended active polyelectrolyte multilayer for sensitive protein determination

Herein, we report two simple label-free electrochemical aptasensors for protein detection using layer-by-layer (LBL) self-assembled multilayers with ferrocene-appended poly(ethyleneimine) (Fc-PEI), carbon nanotubes (CNTs) and aptamer. In one sensing strategy, the Fc-PEI, CNTs and DNA aptamer are LBL assembled on the electrode surface via electrostatic interaction. In the presence of target, the aptamer on the outermost layer of the LBL self-assembled multilayer would catch the target on the electrode interface, which makes a barrier for electrons and inhibits the electro-transfer, resulting in the decreased DPV signals of Fc-PEI. Using this strategy, a wide detection range (0.3–165 ng ml−1) for model target thrombin is obtained, with a low detection limit of 0.14 ng ml−1. In the similar sensing strategy for detection of lysozyme, a wide detection range (0.2 ng ml−1 to 1.66 μg ml−1) and a low detection limit (0.17 ng ml−1) are obtained. These results prove that the LBL sensing strategies developed possess sensitivity, selectivity, stability and generality.