Label-free tracking of single extracellular vesicles in a nano-fluidic optical fiber
||E. van der Pol, S. Weidlich, Y. Lahini, F.A.W. Coumans, A. Sturk, R. Nieuwland, Markus A. Schmidt, S. Faez, and T.G. van Leeuwen|
||SPIE Photonics West 2016, San Francisco, United States|
||February 13, 2016|
Extracellular vesicles are present in body fluids and have promising clinical applications. Thus far, vesicles <70 nm have never been studied in their physiological environment. We contained urinary vesicles within a single-mode light-guiding silica fiber with a 600 nm nano-fluidic channel. Laser light was coupled to the fiber, resulting in a strongly confined optical mode, which illuminated the vesicles. Light scattering from the vesicles was collected and imaged with a home-built microscope. For the first time, we have studied vesicles <70 nm freely diffusing in suspension. The ease-of-use and performance of this technique support its potential for vesicle-based clinical applications.
Background: Extracellular vesicles, such as exosomes, are abundantly present in human body fluids. Since the size, concentration and composition of these vesicles change during disease, vesicles have promising clinical applications, including cancer diagnosis. However, since most vesicles have a diameter <70 nm, detection of single vesicles remains challenging. Thus far, vesicles <70 nm have only be studied by techniques that require the vesicles to be adhered to a surface. Consequently, the majority of vesicles have never been studied in their physiological environment. We present a novel label-free optical technique to track single vesicles <70 nm in suspension.
Method: Urinary vesicles were contained within a single-mode light-guiding silica fiber containing a 600 nm nano-fluidic channel. Light from a diode laser (660 nm wavelength) was coupled to the fiber, resulting in a strongly confined optical mode in the nano-fluidic channel, which continuously illuminated the freely diffusing vesicles inside the channel. The elastic light scattering from the vesicles, in the direction orthogonal to the fiber axis, was collected using a microscope objective (NA=0.95) and imaged with a home-built microscope.
Results: We have tracked single urinary vesicles as small as 35 nm by elastic light scattering. Please note that vesicles are low-refractive index (n<1.4) particles, which we confirmed by combining data on thermal diffusion and light scattering cross section.
Conclusions: For the first time, we have studied vesicles <70 nm freely diffusing in suspension. The ease-of-use and performance of this technique support its potential for vesicle-based clinical applications.