A new type of rapid diagnostic testing for infectious diseases such as COVID-19 is the subject of Ph.D. research by Sophia E. Shanko, mechanical engineering student at Eindhoven University of Technology. Shanko’s thesis examines the process used in lab-on-chip technologies that mixes test samples with detection molecules that bind to the virus and emit light or some other signal. The goal was to accelerate the binding process with magnetic particle mixing.

The advantages of incorporating lab-on-chip technologies in test devices include their wide range of applicability, small size and fast analysis capabilities. For example, to test for the presence of a target molecule, such as an antibody that signals the presence of the virus, a blood sample is combined with a fluid containing the detection molecules that can bind to the target molecule. The detection molecule Photo captures magnetic microbead dynamics in the presence of mushroom-shaped structures. Source: Eindhoven University of Technologygenerates a signal — such as light — when it binds with the target.

"The binding process in these devices needs to be fast and accurate, and this can be achieved by ensuring that the detection molecules are thoroughly mixed with the test sample as soon as possible," said Shanko. "The very small dimensions of lab-on-chip technologies allow mixing only by molecular diffusion, the inherent motion of molecules within a fluid due to temperature and concentration differences. However, this is a time-consuming process."

Shanko chose to use magnetic forces, an active method, to accelerate molecular diffusion because they produce high and controlled mixing capabilities at a relatively low cost. The detection process accelerates by increasing the chances of target-detection molecule binding events.

The microbead swarm, similar to how birds swarm, is an example of dynamic mixing. Shanko also examined other ways to achieve this with external static mushroom-shaped magnetic structures to help induce mixing. "Although the mushroom-shaped structures can generate very high fluid velocities that could induce efficient mixing, they ended up negatively affecting the overall mixing process," Shanko found.

She also tried attaching magnetic flaps controlled using an external magnetic field to the base of the devices. “The microflaps do improve mixing of the detection molecules in the sample, but further experiments are required to better understand their effect," Shanko added.