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 10-10⁶ 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.

外泌体是液体活检的潜在生物标志物，为以无创方式进行早期癌症诊断提供了有希望的机会。然而，直接分析复杂生物样品中的外泌体仍然具有挑战性。在此，提出了一种胆固醇识别测定法，用于通过金纳米粒子 (Au NPs) 标记的电感耦合等离子体质谱法检测外泌体。具体而言，通过anti-CD63捕获外泌体，然后将胆固醇修饰的滚环扩增产物插入外泌体的膜中进行信号放大。同时，制备了 Au NPs 标记的 DNA 用于标记和读出信号。所提出的方法实现了外泌体浓度在 10-10 ^{6范围内的量化}颗粒/μL，检测限为 1.5 个颗粒/μL。将该方法应用于人血清中外泌体的免纯化直接检测，分析结果与纳米粒子追踪分析结果一致。实际样本分析表明，口腔鳞癌患者血清中的外泌体浓度高于健康志愿者血清中的浓度。该方法灵敏、选择性、准确，可用于人血清中外泌体的直接检测，为基于外泌体的液体活检在早期癌症诊断中提供了新的机会。