Marie-Caroline Jullien

 

Institut de Physique de Rennes

 

Influence of hydrodynamics on adsorption regimes at a solid surface

 

Many scenarios involve the capture of molecules or particles onto functionalized surfaces under laminar flow conditions, such as in classical biomedical assays, lab-on-a-chip devices, or biological research protocols. In this presentation, we will explore this topic through two examples: weakly diffusive micrometric particles and small DNA molecules. Specifically, we address the question of interpreting the capture signal while accounting for the flow properties in a straight microfluidic channel.
In the case of micrometric particles, we demonstrate that these particles are subject to a competition between two weak mechanisms: diffusion toward the functionalized surface and lift forces that expel them away from it. This competition leads to markedly different capture behaviors, the occurrence of which depends on the value of a dimensionless parameter, referred to as NLD, which we will introduce. We provide the particle distribution in the liquid along the channel, resulting from this competition, for various NLD values. The proposed model is expected to extend to any transverse force that can be expressed in the form of a potential energy. Ultimately, we predict the capture rate as a function of this dimensionless number over five orders of magnitude (capture flux/NLD value, see figure).
If time permits, we will discuss a second configuration involving the measurement of the adsorption kinetic constant of molecules, typically obtained through Langmuir curves. These methods require large liquid volumes and numerous experiments at different concentrations. We will show that the flow properties enable the measurement of the kinetic constant under non-equilibrium conditions based on a experiment at a single concentration.