Dual-Wavelength Surface Plasmon Resonance for Determining the Size and Concentration of Sub-Populations of Extracellular Vesicles.

Accurate concentration determination of subpopulations of extracellular vesicles (EVs), such as exosomes, is of importance both in the context of understanding their fundamental biological role and of potentially using them as disease biomarkers. In principle, this can be achieved by measuring the rate of diffusion-limited mass uptake to a sensor surface modified with a receptor designed to only bind the subpopulation of interest. However, a significant error is introduced if the targeted EV subpopulation has a size, and thus hydrodynamic diffusion coefficient, that differs from the mean size and diffusion coefficient of the whole EV population and/or if the EVs become deformed upon binding to the surface.

Methods for the physical characterization and quantification of extracellular vesicles in biological samples.

Background: Our body fluids contain a multitude of cell-derived vesicles, secreted by most cell types, commonly referred to as extracellular vesicles. They have attracted considerable attention for their function as intercellular communication vehicles in a broad range of physiological processes and pathological conditions. Extracellular vesicles and especially the smallest type, exosomes, have also generated a lot of excitement in view of their potential as disease biomarkers or as carriers for drug delivery.

A simple model for the resonance shift of localized plasmons due to dielectric particle adhesion.

Ultrasensitive detectors based on localized surface plasmon resonance refractive index sensing are capable of detecting very low numbers of molecules for biochemical analysis. It is well known that the sensitivity of such sensors crucially depends on the spatial distribution of the electromagnetic field around the metal surface. However, the precise connection between local field enhancement and resonance shift is seldom discussed.