A sensitive and label-free electrochemical impedance biosensor for protein detection based on terminal protection of small molecule-linked DNA

In this paper, a label-free electrochemical impedance biosensor has been developed for protein detection based on terminal protection of small molecule linked-DNA. This strategy was demonstrated using folate (FA) and its binding protein folate receptor (FR) as a model case. In the present terminal protection system, with the increase of FR, it could protect more FA linked-DNA from hydrolysis by exonuclease I (Exo I), resulting in an increased electron transfer resistance response. By taking the advantage of the terminal protection assay, this label-free electrochemical biosensor achieved highly sensitive and selective detection of FR with a detection limit of 3 pM and a linear range from 10 pM to 500 nM, which was lower than some previously reported methods. Moreover, the label-free method did not need specific labelling and showed sequence-independent with DNA probes. Thus, it may offer a simple, cost-effective, highly selective and sensitive platform for electrochemical impedance detection of small molecule–protein interactions in clinical diagnostics.