Label-free ratiometric DNA detection using two kinds of interaction-responsive emission dyes.

A novel ratiometric method with label-free and dual-wavelength signal outputs was developed for DNA detection by employing two kinds of structure-specific dyes that characterising interaction-responsive emission property. The ratiometric platform for the fluorescent detection of DNA was based on target-induced structural transformation from stem-loop structure incorporating split G-quadruplex (SISG) to doubule-strand DNA (dsDNA). The SISG conformation will be disrupted upon binding to the target DNA of perfect complementary sequence, resulting in fluorescence decrease at 610nm as NMM releases from SISG and fluorescence increase at 450nm as DAPI inserts into the dsDNA. The method demonstrated its simplicity in that it saved the trouble of expensive and cumbersome functionalization process compared with reported ratiometric methods, and that the two dyes could be excited at the same excitation wavelength. More intriguingly, the combinatorial employment of the two kinds of structure-selective dyes demonstrated a result of "heterosis", in that this sensor simultaneously inherits the sensitivity of DAPI-based signal and the selectivity of G4-based signal. Besides that, this proposed biosensor has been successfully applied in serum sample for DNA detection, and provided a simple and sensitive method for potential DNA detection in bioanalysis, food analysis and disease diagnostic.