Sensitive detection of exosomes by gold nanoparticles labeling inductively coupled plasma mass spectrometry based on cholesterol recognition and rolling circle amplification.

Exosomes, potential biomarkers for liquid biopsy, provide a promising opportunity for early cancer diagnosis in a noninvasive manner. However, direct analysis of exosomes in complicated biological samples is still challenging. Herein, a cholesterol recognition assay was proposed for detection of exosomes by gold nanoparticles (Au NPs) labeling inductively coupled plasma mass spectrometry. Specifically, exosomes were captured by anti-CD63, and then cholesterol-modified rolling circle amplification product was inserted into the membrane of exosomes for signal amplification. Simultaneously, Au NPs-labelled DNA was prepared for labeling and read-out signal. The proposed method achieved the quantification of the exosome concentration in a range of 10-10 particles/μL with a limit of detection of 1.5 particles/μL. The method was applied for the direct detection of exosomes in human serum in a purification-free way, and the analytical result coincided with that obtained by nanoparticle tracking analysis. Real sample analysis manifested that the exosome concentration in the serum of oral squamous cell carcinoma patients was higher than that in the healthy volunteers' serum. The developed method is sensitive, selective, accurate and can be used for the direct detection of exosomes in human serum, providing a new opportunity for exosome-based liquid biopsy in early cancer diagnosis.