Light-Induced Material Motion Fingerprint - A Tool Toward Selective Interfacial Sensitive Fractioning of Microparticles via Microfluidic Methods

In this article, a novel strategy is presented to selectively separate a mixture of equally sized microparticles but differences in material composition and surface properties. The principle relies on a photosensitive surfactant, which makes particles under light illumination phoretically active. The latter hovers microparticles from a planar interface and together with a superimposed fluid flow, particles experience a drift motion characteristic to its interfacial properties. The drift motion is investigated as a function of applied wavelength, demonstrating that particles composed of different material show a unique spectrally resolved light-induced motion profile. Differences in those motion profile allow a selective fractioning of a desired particle from a complex particle mixture made out of more than two equally sized different particle types. Besides that, the influence of applied wavelength is systematically studied, and discussed the origin of the spectrally resolved chemical activity of microparticles from measured photo-isomerization rates. A method is demonstrated for separating microparticles and microplastics distinguished differences in surface morphology (roughness, particles bulk material, and surface functionalization). The method uses advances of microfluidics in combination with illumination of a photosensitive surfactant solution within the shear flow. Spectrally resolved, this yields a light-induced material motion fingerprint allowing a selective fractioning of microparticles via difference in velocity. image