Single-Cell Detection of Circulating Tumor Cells by a Proximity-Enabled Singlet-Oxygen Chemiluminescence Assay

Circulating tumor cell (CTC) assays with single-cell sensitivity and efficient implementation are critically needed in clinic applications, especially for cancer screening. We report a novel proximity-enabled singlet-oxygen chemiluminescence assay (PESCA) that enables low-cost and efficient CTC detection with single-cell sensitivity. The PESCA system is based on proximity labeling of cell-surface oncoprotein markers on CTCs using two types of polymer nanoparticles, one for generating singlet oxygen (¹O₂) and the other for activating chemiluminescence upon ¹O₂ sensitization and H₂O₂ decaging. A hybridization chain reaction (HCR) is exploited for triggering the proximity labeling, allowing efficient sensitization of the chemiluminescence signal specific to CTCs with signal amplification to enable robust single-cell resolution. The PESCA method can accomplish digital counting of CTCs in a whole blood sample with a detection efficiency of 80% for 10 CTCs in 7.5 mL of whole blood, highlighting its potential for cancer screening in clinic applications.