A sandwich-based evanescent wave fluorescent biosensor for simple, real-time exosome detection^†

Exosomes are regarded as a promising biomarker for the noninvasive diagnosis and treatment of diseases. The value of exosomes for medical research has promoted the search for a fast, efficient, and sensitive detection method. This study reported a sandwich-based evanescent wave fluorescent biosensor (S-EWFB) for exosome detection. A two-step strategy was implemented to take advantages of the simple binding of fluorescent probes with exosomes via the hydrophobic interaction between the cholesteryl and phospholipid bilayer membrane, as well as real-time detection on an evanescent wave liquid-solid interface based on CD63 aptamer-specific capture to form an exosome@fluorescence probe/aptamer sandwich structure. The one-to-many connection between exosomes and signal molecules and the aptamer-modified evanescent wave optical fiber detection platform reduced the detection limit of exosomes to 7.66 particles/mL, with a linear range of 47.5-4.75 × 10⁶ particles/mL. The entire detection process was simple, rapid, and real-time and lasted about 1 h while requiring no separation and purification. Additionally, this platform showed excellent surface regeneration capability and exhibited good performance during the analysis of tumor and non-tumor-derived exosomes.