Microfluidic Diffusional Sizing (MDS)

A new class of in-solution protein
affinity measurement

Where interaction measurement

becomes robust and easy


Quantify binding events in solution, in their native state & native environments.


No immobilization or purification. Just mix and measure.


For high and low affinity, for both simple and complex systems.


Minimum sample required, especially for clinical samples.


Size, binding affinity (KD), stoichiometry and concentration all at once.


No calibration, no prior biophysical knowledge required.

How it works

Microfluidic Diffusional Sizing (MDS) measures molecular size (hydrodynamic radius) of a sample by evaluating its diffusion in a microfluidic chamber.

Fluorescently labelled proteins enter the microfluidic diffusion chamber together with an auxiliary fluid, in two parallel laminar streams.

The rate of diffusion of proteins from one stream to the other depends on the protein molecular size.

The rate of diffusion and hydrodynamic radius (Rh) of the protein can be calculated based on the ratio of fluorescence signal detected in the two streams at the end of the chamber.

Changes in size reveal protein interactions


The size of the protein is measured in free form and against a titration of binding partner, allowing construction of a binding curve and calculation of binding affinity (KD).

Obtain concentration & affinity simultaneously


The concentration of active binding sites can be determined by measuring binding at different concentrations of the labelled protein. This provides a calibration-free measurement of concentration in complex samples such as biofluids or crude membrane preparations.

Concentration data can also be used to determine binding stoichiometry (number of binding sites per molecule).

See how proteins truly interact

Tackle your most challenging targets, in the most complex backgrounds

From traditional to challenging targets

  • Globular proteins
  • DNA
  • Antibodies
  • Bispecific antibodies
  • Amyloid fibrils
  • Polyclonal antibodies
  • Disordered proteins
  • Membrane proteins

In purified or complex backgrounds

  • Buffers
  • Purified samples
  • Diluted serum and plasma
  • Fermentation broth
  • Saliva
  • Serum and plasma
  • Cell lysate
  • Tissue homogenate
  • Clinical samples

Accelerate your drug development process

MDS enables a wide range of applications throughout different stages of drug development process.

Basic Research

  • Measure binding and activity of your most challenging targets
  • Unlock competition experiments and work with ternary complexes

Drug discovery

  • Validate and characterize hits without having to purify
  • Optimize leads and understand their mechanism of action

Translational Research

  • Obtain concentration and affinity of serum antibodies and overcome limitations imposed by ELISA titers
  • Evaluate immune responses directly in patient samples (e. g., vaccine development)

See MDS in action with the Fluidity One-M system

Learn how you can get MDS up and running for your project with the Fluidity One-M system.

Fluidic Sciences Ltd