Microfluidic diffusional sizing (MDS) exploits the propensity of fluids to flow in a laminar state when confined to small (micrometre) length scales. Consequently, when two streams of fluid, one containing particles of interest and the other containing exclusively buffer, meet in a microfluidic channel, there is no convective mixing. Transport of the molecules into the buffer perpendicular to the direction of the flow lines proceeds, in the absence of an applied force, exclusively via diffusion (Weigl, Science, 1999). The rate of diffusion is related to the hydrodynamic radius (Rh) of the particles, and so provided that the streams can then be separated, and the quantity of particles in each stream subsequently quantified, the average Rh of the particles in solution can be calculated.
This approach, when coupled with protein detection following measurement, can be used to determine Rh of proteins in solution. Our Fluidity One uses a proprietary "latent" label - a dye that only fluoresces following reaction with free amine groups on proteins or peptides. This ensures sensitivity by minimising background signal, and enables quantification of total protein, and calculation of Rh.