Integrating OCT with flow cytometry for enhanced detection of extracellular vesicles

Extracellular vesicles (EVs) are biological particles, 50-1000 nm in diameter, released by cells into the bloodstream. They can serve as disease biomarkers due to their parent cell and organ-derived content.Traditional flow cytometers, which rely on incoherent light scattering, often lack the sensitivity to detect EVs smaller than 100-200 nm amidst background signals. Our research aims to develop a flow cytometry system where EV backscattered light is detected using optical coherence tomography (OCT). Using a home-built fluidic and optical system, we demonstrate the detection of sub-200 nm polystyrene beads in flow at a rate of 1000 counts per second. We show that the detected scattered signal is consistent with Mie theory, which can be used for particle size determination. Using the infrared spectrum and detection in backscatter geometry, the proposed technique can be integrated into conventional flow cytometers that use forward and side scatter modalities. Furthermore, by providing higher contrast signals, the integration of OCT can improve sensitivity and detect smaller EVs than is currently possible.