Label-free and dye-free detection of target DNA based on intrinsic fluorescence of the (3+1) interlocked bimolecular G-quadruplexes

The intrinsic fluorescence of the interlocked bimolecular DNA G-quadruplex (93del4T) was utilized to achieve label-free and non-toxic detection of target DNA. The designed probe consists of a single stranded DNA template that hybridizes with the sequence of 93del4T at 5' end forming partial complementary duplex and leaving single strand overhang at 3' terminus to recognize target DNA molecule. Once the target DNA hybridizes with the probe to form another part of duplex at 3' terminus, exonuclease. will catalyze the stepwise removal of nucleotides from the blunt 3' terminus, consecutively liberating the target DNA and the sequence of 93del4T. The released target DNAs can recycle to bind more probes and release more 93del4T that can fold into G-quadruplexes to amplify fluorescence signals. As a result, quantitative detection of the target DNA in human serum has been achieved according to fluorescent signal intensities. In comparison to other methods, this strategy is simple, rapid, inexpensive and toxic free.