Single-Vesicle Infrared Nanoscopy for Noninvasive Tumor Malignancy Diagnosis

Protein heterogeneity in molecular expression and structures determines tumorigenesis and is the diagnostic and therapeutic cancer biomarker. Small extracellular vesicles (sEVs) are cell-released nanoscaled membrane-bound vesicles transferring bioactive molecules for intercellular communication and playing essential roles in tumor progression and metastasis. Therefore, protein heterogeneity in tumor-derived sEVs indicates the degree of malignant transformation, providing a noninvasive biomarker for cancer diagnosis and malignancy evaluation. We employ near-field infrared (nano-FTIR) spectroscopy to investigate malignancy-related protein heterogeneity in a single sEV and demonstrate the discriminability of sEV protein heterogeneity to evaluate tumor malignancy and metastasis. We found that the amide I/II adsorption ratio of the sEVs increases with tumor malignancy, the proportion of α-helix + random coil (α-helix and random coil) in sEV proteins decreases with tumor malignancy, and the proportion of β-sheet + β-turn (β-sheet and β-turn) increases with tumor malignancy. These nano-FTIR spectral signatures of the sEVs from the primary tumor tissue of breast cancer patients show high sensitivity and specificity in evaluating tumor metastasis. This study shows the advantages of nano-FTIR in single sEV characterization and demonstrates the significance of sEV protein heterogeneity in cancer diagnosis. It provides a noninvasive solution to elucidate cancer development and facilitates the exploitation of potential cancer biomarkers.