Highly sensitive ratiometric fluorescent paper sensor for the urine assay of cancer

Telomerase, as a valuable biomarker, is an important target in cancer diagnosis. Here, we report a ratiometric fluorescent probe for telomerase activity assay in urine and bladder cancer diagnoses based on the color change of Rox-DNA functionalized quantum dots (QDs). The green fluorescence of the QDs was sensitive to H 2 O 2 , but the red fluorescence of Rox showed no change. An HRP-mimicking hemin/G-quadruplex, which was formed with the help of telomerase activity, catalyzed H 2 O 2 into H 2 O and O 2 . This quadruplex effectively avoided H 2 O 2 interference with green fluorescence. In the presence of H 2 O 2 , the detected color changed from red to yellow-green by increasing the telomerase concentration. The detection limit (LOD) was 10 cells, and response time was within 60 min. More importantly, a paper sensor was developed based on this probe and used for the assay of telomerase activity in urine samples. The results were highly sensitive and reproducible, and visual semi-quantitative detection was realized using the naked eye.