Colorimetric aptasensor based on temporally controllable light-stimulated oxidase-mimicking fluorescein for the sensitive detection of exosomes in mild conditions.

Analysis of exosomes provides important information for rapid and non-invasive screening of tumors. However, sensitive and convenient detection of exosomes remains technically challenging to date. Herein, a colorimetric aptasensor based on the light-stimulated oxidase-mimicking activity of FITC was constructed for detecting ovarian cancer (OC) exosomes. The aptasensor contained an EpCAM aptamer to capture OC exosomes. Cholesterol and fluorescein (FITC) were used to modify either end of the DNA (DNA anchor). The DNA anchor could combine with exosomes through a hydrophobic reaction between cholesterol and the lipid membrane. FITC oxidized 3,3',5,5'-tetramethylbenzidine (TMB) under a 365 nm LED light source in a temporally controllable manner under mild conditions, causing the solution to change from colorless to blue, and the corresponding UV-vis absorbance increased. Based on this principle, the exosomes were qualitatively analyzed by observing the color change with the naked eye. In parallel, the exosome concentration was also detected using UV-vis spectrophotometry. The linear range was from 2 × 10 to 100 × 10 particles per mL with a limit of detection of 1.77 × 10 particles per mL. The developed aptasensor also exhibited favorable selectivity and could discriminate the exosomes from OC cells and normal cells. Besides, the receiver operating characteristic (ROC) curve demonstrates that it is possible to distinguish between patients with OC and healthy donors (HDs) using exosomes as the biomarker. Our technology may expand the applications of DNA-based detection method-enabled OC diagnostic tools.