Dual-mode exosome detection leveraging a nanozyme-active artificial receptor: PDA@Fe@Zn-based nucleic acid aptamer sensor

Exosomes, extracellular vesicles crucial for intercellular communication, are emerging as significant biomarkers for disease diagnosis, especially in cancer. This study presented a dual-mode exosome detection platform using polydopamine microspheres doped with iron and zinc ions (PDA@Fe@Zn). These materials served as both artificial receptors for nucleic acid aptamers and nanozymes with peroxidase-like activity. By integrating colorimetric and fluorescence detection, the platform enables cross-validation of results. PDA@Fe@Zn nanozymes catalyzed the TMB-H₂O₂ reaction under acidic conditions, producing a colorimetric signal proportional to exosome concentration. Concurrently, the fluorescence of FAM-labeled aptamers was dynamically quenched by PDA@Fe@Zn and the presence of exosomes restores the fluorescence signal for a "turn-on" detection mode. DNase I amplified detection signals by cleaving bound exosomes for multiple cycles, achieving a limit of detection (LOD) of 4.7 × 10⁴ particles/mL for colorimetric detection and 2.2 × 10⁴ particles/mL for fluorescence detection. Notably, the colorimetric platform revealed that the relative expression of the CD63 protein on exosomes from breast cancer cells MCF-7 and MDA-MB-231 was approximately 2.7 and 2.4 times higher, respectively, than in normal breast cells MCF-10A; similar fold changes of 2.9 and 2.4 were observed with fluorescence detection, underscoring the robustness of the dual-mode system. The platform demonstrated rapid detection (within 30 min), high sensitivity, strong anti-interference capability, and the ability to distinguish exosomes from cancerous and normal cells effectively.