Monolithically-integrated cytometer for measuring particle diameter in the extracellular vesicle size range using multi-angle scattering.

Size measurement of extracellular vesicles is hampered by the high cost and measurement uncertainty of conventional flow cytometers which is mainly due to the use of non-specialised free space optics. Integrated cytometry, where the optics and fluidics are embedded in a monolithic chip shows promise for the production of low cost, micro-flow cytometers dedicated for extracellular vesicle (EV) analysis with improved size measurement accuracy and precision. This research demonstrates a unique integrated cytometer for sub-micron particle size measurement using multi-angle scattering analysis. A combination of three technologies is used: (i) Dean-based hydrodynamic focussing to deliver a tight sample core stream to the analysis region, (ii) integrated waveguides with multimode interference devices to focus a narrow excitation beam onto the sample stream, and (iii) an angular array of collection waveguides to measure particle scattering distribution and calculate diameter. Low index 200 nm liposomes could be detected and polystyrene size standards as small as 400 nm diameter could be measured with an uncertainty of ±21 nm (1/2 IQR) demonstrating a first step on the path to high performance integrated cytometry of EVs.