23 May 2013 Small angle light scattering characterization of single micrometric particles in microfluidic flows
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A CCD-camera based small angle light scattering (SALS) apparatus has been used to characterize single micrometric particles flowing in a micro-channel. The measured scattering vector spans the range 2x10-2 - 6:8x101μm-1. The incident laser light is collimated to a spot of about 50 μm in diameter at the sample position with a divergence lower than 0.045 rad. Such small collimated laser beam opens the possibility to perform on-line SALS of micron-sized particles flowing in micro-channels. By properly designing the micro-channel and using a viscoelastic liquid as suspending medium we are able to realize a precise 3D focusing of the target particles. The forward scattering emitted from the particle is collected by a lens with high numerical aperture. At the focal point of that lens a homemade beam stop is blocking the incident light. Finally, a second lens maps the scattered light on the CCD sensor, allowing to obtain far field images on short distances. Measurements with mono-disperse polystyrene particles, both in quiescent and in-flow conditions have been realized. Experiments in-flow allow to measure the single particle scattering. Results are validated by comparison with calculations based on the Lorenz-Mie theory. The quality of the measured intensity profiles confirms the possibility to use our apparatus in real multiplex applications, with particles down to 1 μm in radius.
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David Dannhauser, David Dannhauser, Giovanni Romeo, Giovanni Romeo, Filippo Causa, Filippo Causa, Paolo A. Netti, Paolo A. Netti, "Small angle light scattering characterization of single micrometric particles in microfluidic flows", Proc. SPIE 8792, Optical Methods for Inspection, Characterization, and Imaging of Biomaterials, 879212 (23 May 2013); doi: 10.1117/12.2022154; https://doi.org/10.1117/12.2022154

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