Label-free and ratiometric fluorescent nanosensor based on amino-functionalized graphene quantum dots coupling catalytic G-quadruplex/hemin DNAzyme for ultrasensitive recognition of human telomere DNA

•Ultrasensitive ratiometric fluorescent nanosensor was established based on af-GQDs.•Catalytic G-quadruplex/hemin DNAzyme was used to oxidize OPD to colored DAP.•Af-GQDs were used as the reference and DAP was used as the response signal.•Ultrahigh sensitivity and excellent specificity are achieved by the label-free strategy.•Human telomere DNA can be distinguished by fluorescence and naked eyes.

Ultrasensitive determination of human telomere DNA is quite important in early diagnosis of generalized diseases and biodefense applications. Herein, we present a label-free and ratiometric fluorescent nanosensor for ultrasensitive determination of human telomere DNA based on amino-functionalized graphene quantum dots (af-GQDs) coupling catalytic G-quadruplex/hemin DNAzyme for the first time. During this strategy, af-GQDs are utilized as the reference fluorophore and 2,3-diaminophenazine (DAP) is chosen as the specific response signal. The fluorescence intensity of DAP at 553 nm increases significantly with a simultaneous fluorescence quenching of af-GQDs at 440 nm with the increase of G-quadruplex/hemin DNAzyme, resulting in a label-free and ratiometric fluorescent nanosensor toward human telomere DNA. This nanosensor exhibits broad linear range (0.2 pM ∼ 50 pM), excellent sensitivity toward human telomere DNA recognition (LOD = 25 fM), and excellent selectivity for human telomere DNA over some biomolecules. This strategy is promising for the detection of any short oligonucleotides by altering the target recognition unit and avoiding the complex modification process.

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