Ultrasensitive detection of hERG potassium channel in single-cell with photocleavable and entropy-driven reactions by using an electrochemical biosensor.

Ion channel is a pore-forming membrane protein that allows ions to pass through the cell membrane， which is essential for the continuation of life. Analysis of ion channel characteristics at the single cell level will help to study the role of cellular heterogeneity in disease progression and cellular signaling processes. In this study， we fabricate a photocleavable and entropy-driven reaction based electrochemical biosensor for ultrasensitive detection of human ether-a-go-go related gene (hERG) potassium channel activity on HEK293 cell. We employed an antibody-DNA1 to conjugate the hERG channel in the cell membrane via antibody-antigen reaction. The release of the DNA1 by photocleavable reaction will trigger an amplification reaction by using the Exonuclease III (Exo III) to generate intermediate DNA. In addition， two hairpin DNA (DNA3 and DNA4) was employed for the signal amplification. We well designed a toehold on DNA3 for intermediate DNA hybridization to form double-strand DNA that opens the DNA3 hairpin. The free DNA3 exposed the relocked toehold domain to open the DNA4. After the entropy-driven toehold-mediated displacement amplification reaction by using intermediate DNA， DNA4 hybridized with DNA3 effectively， making the ferrocene labeled on the 5'-termini DNA4 close to the Au electrode surface to produce the electrochemical response. Then， the displaced intermediate DNA was released from the cell surface into solution for the next entropy-driven reaction. After two steps amplification reaction， one ion channel triggered thousands of DNA3/DNA4 duplex on the biosensor surface. By using this biosensor， electrochemical curve of hERG ion channels on a single cell was obtained.