What is Microfluidic Diffusional Sizing (MDS)?

Published on September 10th, 2019

Microfluidic diffusional sizing (MDS) exploits the unique properties of “flow” in microfluidic channels — specifically laminar flow, where streams can flow alongside one another with no convective mixing. MDS measures molecular size (hydrodynamic radius), and changes in size indicate binding events.

The interactions of proteins with secondary molecules is of great importance across the life sciences. Understanding how proteins bind with other secondary molecules is the key to combating diseases. The Fluidity One Platform uses MDS technology to determine the binding affinity between proteins and their binding partners; whether they are aptamers, lipids, DNA, small molecules or other proteins.


What is Microfluidic Diffusional Sizing (MDS)?

Watch the video below to understand how Microfluidic Diffusional Sizing works:

How MDS works

In MDS, two streams of liquid are introduced into two separate but parallel channels, which flow next to each other, one stream being the sample, in which there is a labelled protein and an unlabeled potential binding partner, the other stream being, for example, buffer only.

Because there is no convective mixing, the only way your protein can migrate into the auxiliary stream is by diffusion, the rate of which will depend on the size of the protein. Small proteins will diffuse very rapidly, and large proteins more slowly. Diffusion can occur at any point along the length of the diffusion chamber, but at the end the streams are re-split, and at this point the degree of diffusion is fixed.

If there is a “binding event” in a sample, between the labelled protein and the binding partner, the resulting bound complex will be larger than the unbound labeled protein, and it will not diffuse as far into the parallel channel as it would if binding had not occurred

Once the liquids have been allowed to flow in their adjacent parallel channels in the diffusion chamber, they are then split again into two channels, and the hydrodynamic radius of the molecules in each of the two channels post-diffusion is then measured.

The extent of that diffusion can be accurately measured, such that in a single experiment, information can be obtained regarding affinity (KD), concentration and stoichiometry, all under physiologically-relevant conditions.

The quantity of protein in each stream is determined using an amine reactive fluorogenic dye. The combined total fluorescence is used to determine the concentration of protein in solution, and the ratio of fluorescence between the two streams used to determine the diffusion co-efficient of the protein, which in turn is used to determine the protein’s hydrodynamic radius.

Because diffusion occurs while the protein is in its native state, the reported size is that of the native protein in solution. And because this process all takes place in microfluidic volumes, the measurement can be performed quickly and with minimal sample input.

Therefore, in very broad terms, the ability of MDS to make such measurements can accurately enable the biophysical characterization of many kinds of molecular interactions. The potential applications of MDS are thus far-reaching, and in the life sciences arena they include the study of protein interactions with antigens, or other proteins, DNA or lipids, to name but a few.


Microfluidic diffusional sizing (MDS) in the literature:

If you would like to learn more about microfluidic diffusional sizing (MDS) you can find a summary of all the papers showing the research behind Fluidic Analytics and microfluidic diffusional sizing (MDS) here. As well as seeing where others have used our products to make amazing discoveries.