Terminal protection G-quadruplex-based turn-on fluorescence biosensor for H5N1 antibody

A label-free, facile, G-quadruplex-based, turn-on biosensor has been developed for the detection of H5N1 antibody using quinaldine red as G-quadruplex-binding probe. The small molecule-DNA chimaeras are preserved from digestion by 3'-5' exonuclease III on account of the terminal protection of a double-strand DNA in view of specific affinity and specificity between antigen peptide fragments and antibody. Upon the digestion of the unprotected DNA strand by 3'-5' exonuclease III, the released G-rich strand forms a quadruplex in the presence of potassium ion and binds to a particular G-quadruplex binder, quinaldine red, which results in a prominent increase in fluorescence. The assay deserves a straightforward design and operation, no sophisticated operating steps are required. The method has been applied to detect H5N1 antibody with a detection limit of 0.3 nM without the use of radiolabeled or fluorescently labeled oligonucleotides.