EV trapping: Raman characterization of single tumor-derived extracellular vesicles

The search for cancer biomarkers of easy access and with diagnostic and prognostic value has led to a growing interest in very small particles that are released not only by healthy cells but also by cancer cells. These membrane bound particles, known as extracellular vesicles (EVs), may be present in body fluids of cancer patients, such as in the blood. The idea of detecting and distinguishing these tumor-derived extracellular vesicles (tdEVs) from other small particles in body fluids has motivated us to explore and develop technology that can distinguish single tdEVs from other particles. The aim of this thesis is to detect and characterize biological nanoparticles in blood, specifically tdEVs, at the single particle level. Hence, this thesis explores various methods that enable, in a novel way, the detection and chemical characterization of individual particles and the discrimination of tdEVs from other EVs and non-EV particles, such as lipoprotein particles, in a label-free manner. One method explored is the correlation of scanning electron microscopy (SEM) and Raman spectroscopy that enables the acquisition of high resolution SEM images and the spatial correlation with chemical information as obtained from Raman micro-spectroscopic imaging. Another method is the development of optical trapping and synchronized Rayleigh and Raman scattering (OT-sRRs) for the detection and characterization of single biological nanoparticles, such as tdEVs, directly in suspension and in a label-free manner. This thesis describes the implementation of various novel methods to study biological nanoparticles in blood, from cancer cells to tdEVs and from model nanoparticles to nanoparticles in the plasma of cancer patients. These developments open an avenue not only to exploit the potential of tdEVs as cancer biomarkers, but also to study other particles in body fluids and, with that, the general nanoparticle profile, which may be affected under pathological conditions such as cancer.