FEM analysis of magnetic agitation for tagging biomolecules with magnetic nanoparticles in a microfluidic system

In a microfluidic system, magnetic nanoparticles (MNPs) tagged with biomolecules can be efficiently used for separation and detection. Tagging various fluid contents continuously in the micro-scale is often difficult due to slow diffusion process. Therefore, enormous time is needed for biomolecules to be thoroughly mixed and combined with MNPs. In this work, we report a finite-element COMSOL-based model to demonstrate the novel method of tagging biomolecules with MNPs on-chip using time-dependent magnetic field. The oscillating magnetic body forces that act on MNPs cause agitation in the surrounding fluid that otherwise follow laminar profile and overall speed up the reaction kinetics of the tagging process. Based on results, magnetic actuation is a strong function of both magnetic nanoparticle size and switching frequency of magnetic field and for the studied geometrical configuration and flow condition 100 nm MNPs together with 0.1 Hz switching frequency bring out optimum mixing condition. Effect of flow velocity is also studied and from the analysis MNPs actuated tagging process seems to be more profound at an optimum inlet velocity of 50 μm/s. Electrode current and electrode separation are also critical parameters and need to be optimized. For the given configuration, larger separation and higher current produce less agitation effect. Furthermore, magnetic actuation scheme is compared with passive mixing strategy. A 49% increase in tagging performance is observed when MNPs together with magnetic actuation scheme is used as compared to passive method consisting of barriers which only increases the tagging performance by 20%. The strategy demonstrated here is easy to implement and can be integrated on a lab-on-a-chip system. Overall, the developed COMSOL model demonstrates that time-dependent magnetic actuation is an efficient tool to tag MNPs with biomolecules in situ for the development of efficient point-of-care microfluidic systems.