Single-Molecule Liquid Biopsy Detects Low- and High-Abundance Protein Markers Simultaneously for Pancreatic Cancer Diagnosis

Simultaneous analysis of multiple biomarkers can typically improve the sensitivity and specificity of a disease diagnosis. Low-abundance serum proteins have recently emerged as a novel class of biomarkers for diseases. Due to the low concentration, the low-abundance protein analysis relies on single-molecule immunoassay, which has a very limited dynamic range. As a result, simultaneous analysis of low- and high-abundance protein markers requires multiple instruments, which demands larger sample volumes and is cost-/labor-consuming. To overcome these limitations, we developed a single-molecule imaging technique that can detect low- and high-abundance protein markers simultaneously in one chip. By employing a hybrid biomarker capture strategy that involves both glass surface and bead immobilization, our method greatly extended the detection range of the single-molecule assay. We used the method for pancreatic cancer diagnosis and analyzed three serum biomarkers of different abundances, including LIF, CA19-9, and CA125. Combined analysis of the three biomarkers yielded exceptional sensitivity and specificity (AUC = 0.996), which is better than using any of the markers alone, including CA19-9 that is used in clinical practice (AUC = 0.804). Overall, we demonstrated a simple and cost-effective method that greatly extended the dynamic range of single-molecule imaging while maintaining the sensitivity, which has great potential in various clinical applications.