How does the Fluidity One-W work?

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-W uses microfluidic diffusional sizing (MDS) technology to determine the binding affinity between proteins and their binding partners; whether they are aptamers, lipids, DNA, small molecules or other proteins. Watch the video below to understand how the Fluidity One-W works:


In the Fluidity One-W, a stream of fluorescently labelled protein is introduced into the diffusion chamber alongside an auxiliary stream.

These streams flow in parallel with no convective mixing So the only way protein can migrate from one stream to the other is by diffusion.

Small peptides and proteins diffuse rapidly. Large proteins and aggregates, slowly.

At the end of the diffusion chamber, the streams are split.

The quantity of protein in each stream is determined by the fluorescence from the label.

The ratio of fluorescence between the two streams gives us the protein's hydrodynamic radius.

The Fluidity One-W can measure this with proteins in buffer and in crude solutions like cell lysates or biological fluids.

Because only the labelled species is detected.

If we repeat the test using a mixture of labelled protein and unlabelled binding partner, we can observe the degree of binding due to the change in size.

Only species including the labelled protein are detected and measured.

Titrating the binding partner against the labelled protein gives a binding curve and automatically generates a KD value on screen.

The hydrodynamic radius for the unbound protein and the protein complex are also automatically calculated and displayed.

  • Publications and resources

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    • Posters10 September 2019

      Fluidity One-W protein interactions poster

      Poster summarising the work done by our internal applications team using MDS on protein interactions with proteins, lipids and antibodies as well as other published work using MDS to analyse protein interactions.

    • Application note03 April 2019

      Determination of KD of aptamer protein interactions by microfluidic diffusional sizing

      Here the Fluidity One-W is used to experimentally determine the KD of two protein aptamer interactions, with results in good agreement with literature values. Importantly the technique required no calibration, complex setup or specialist sample preparation. Furthermore, the interaction is assessed without immobilising or altering either molecule beyond the addition of a standard fluorescent label.

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