Construction of a controllable Förster resonance energy transfer system based on G-quadruplex for DNA sensing

Conjugations of oligonucleotides , chromophores , and gold nanoparticles (GNPs) can be used for energy transfer assays to detect DNA . Herein, a homogenous Förster resonance energy transfer (FRET) system employing two-step modification of oligonucleotide on GNPs was reported. The distance between the donor (fluorescein attached onto DNA) and the acceptor (GNPs) was controlled by using the G-rich DNA. In the presence of porphyrin or berberine , which can act as ligands of G-quadruplexes, the G-rich DNA spacer can result into G-quadruplex structure. Therefore, the intimate contact between the fluorophore and the GNP results in efficient energy transfer and fluorescence quenching . After hybridization with target DNA, the G-quadruplex stretched and resulted in an enhancement of fluorescence. So the present FRET system can be used for target DNA sensing with detection limit as low as 40   pM ( S / N =3). In this study, a relation between the fluorescence quenching efficiency and GNP sizes was found and bigger GNPs had higher fluorescence enhancement after hybridization with target DNA.