Diffusiophoresis and diffusioosmosis-driven dynamics of modified polystyrene colloids in long double-junction microchannels

In previous studies, we introduced a double-junction microfluidic device that exploits diffusiophoresis anddiffusioosmosis for size- and charge-based particle separation under continuous flow settings.[1,2] The device establishes a steady-state salt gradient perpendicular to the flow, causing particles to accumulate into two symmetric regions via diffusiophoretic and diffusioosmotic effects. In this work, we investigated the dynamics of particles in longer microchannels, whereby particle residence times are comparable to the characteristic time for salt diffusion. Scaling laws relating the width of the colloidal streams and the distance between particle focusing peaks to the residence time were determined. Furthermore, a general scaling law relating the intensity of the central particle accumulation to particle diameter and zeta potential was established. This relationship can be used to determine one property if another is known. We also investigated the effect of particle and channel surface chemistry, finding that particle migration and focusing is highly sensitive to the presence of a protein layer coating on the particle and channel wall surfaces. By leveraging this effect, we propose a strategy to fully separate protein-coated from bare particles. This approach offers a promising platform for point-of-care diagnostics, including bioparticle sensing, sorting, preconcentration, and analysis.

1 Chakra et al., ACS Nano 17, 14644–14657 (2023)

2 Chakra et al., JCIS 693, 137577, (2025)