In recent years, an increasing interest in harnessing the chemical energy in the form of solute concentration gradient have led to the exploration of colloidal particle manipulation by diffusiophoresis (DP) in microfluidic devices. Transient salt concentration gradients have been successfully used to achieve enhanced particle transport into dead-end structures by DP and diffusioosmosis (DO) effects. In this study, we report a novel mechanism for reversible trapping of particles in dead-end micro-structures via steady-state solute gradients in a continuous flow setting. A microchannel, made of an optical adhesive glue, was fabricated by photo-/soft-lithography techniques and fitted with a transverse microgrooved wall. The charged fluorescent colloidal particles were accumulated within the microgrooves by pumping parallel electrolyte solutions into the device junction. The spatial distribution of particles within the channel was characterized via confocal microscopy and a numerical investigation was carried using finite element simulations. As shown by the confocal scans in the figure, we found that particles accumulate within the flow recirculation region beneath the groove entrance due to a combination of DP transport and hydrodynamic effects. The trapping phenomenon is fully reversible and particles can be cyclically trapped into and released from the grooves by controlling the salt concentration of the parallel streams via a flow switching valve. The proposed method offers great potential for microfluidic bio-analytical testing applications, including bio-particle pre-concentration and signal amplification.

Reversible trapping of colloids in microgrooved channels by diffusiophoresis

ACS Spring Meeting 2021

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