Dissolution without dispersion

Microfluid facilities (Lab-on-Chips) are crucial to the modern biology diagnostic devices (i.e. pregnancy Test Kits or blood-glucose meters). One of the significant processes in these facilities is integrating multiple reagents into one test device by channel flows, which is shown in the figure below. We can see the reagents (small circles) are dissolved in the liquid and then transferred to the test device on the right.

However, the flow not only dissolves the reagents but also disperses them at the same time, causing problems when we would like to separate different species and have ‘reagents sequences’. Researchers in IBM Research — Zurich proposed an idea of ‘stretching a water drop into a long ribbon-like shape in a microchannel the width of a human hair and forcing the liquid to fold over onto itself’ (see the figure below). They called this phenomenon ‘self-coalescence’, which reduces the flow rate where the dried reagents are, so they no longer disperse (see the video from the supplementary from their paper).

Based on this idea, they successfully separated different reagents in the solvents and obtain the ‘reagent sequence’ (see the figure below). 

For more detailed information, please check the paper– ‘Gökçe, O., Castonguay, S., Temiz, Y., Gervais, T., & Delamarche, E. (2019). Self-coalescing flows in microfluidics for pulse-shaped delivery of reagents. Nature574(7777), 228-232.’ and the video at the links below.