A novel biosensor based on DNA hybridization for ultrasensitive detection of NOS terminator gene sequences

In this work, we have successfully designed a novel biosensor based on DNA hybridization for ultrasensitive detection of NOS terminator gene sequences (NOSt). This biosensor was synthesized by connecting single-stranded capture DNA (sDNA)-labeled graphene oxide quantum dots (GOQDs) (QDs-sDNA) as fluorescent probe and graphene oxide (GO) as quencher. The detection principle based on hybridization combinations can occur between QDs-sDNA and complementary target DNA; moreover, QDs-sDNA can bind to GO with significantly higher affinity than QDs-dsDNA. In the absence of complementary target DNA, QDs-sDNA was absorbed onto the surface of GO, and the fluorescence of QDs-sDNA was quenched due to fluorescent resonant energy transfer. In the presence of a complementary target DNA, its hybridization with QDs-sDNA formed QDs-dsDNA, which cannot be adsorbed to the GO surface and this leads to reduced quenching. By comparing the fluorescence intensity of QDs-sDNA and QDs-dsDNA in the presence of GO, we can achieve target DNA detection. Thus, rapid, simple, sensitive, efficient, and eco-friendly detection of NOSt was realized. This biosensor had a detection limit of 0.008 nM and a linear range of 0.05-50 nM. Moreover, this sensor can selectivity detect target DNA compared with random and single-base-mismatched sequences, and was successfully applied to the determination target DNA sequences in biological fluids directly. This sensor can be applied to detect other target DNA sequences by simply changing the types of sDNA coupled to the GOQDs.