Microfluidic diffusional sizing (MDS) analysis of the interactions and sizes of proteins under native solution conditions

Paolo Arosio, Thomas Müller, Luke Rajah, Emma V. Yates, Francesco A. Aprile, Yingbo Zhang, Samuel I. A. Cohen, Duncan A. White, Therese W. Herling, Erwin J. De Genst, Sara Linse, Michele Vendruscolo, Christopher M. Dobson, Tuomas P. J. Knowles.

ACS Nano 10 333-341, 2015.

In this paper from Arosio et al microfluidic diffusional sizing (MDS) is used in combination with pre-labelled fluorescent biomolecules to size and quantify proteins in complex mixtures. Initially, MDS is compared to Dynamic Light Scatter (DLS)—and a good correlation is observed for monodispersed solutions (Figure 1a). However, the analysis of a polydispersed solution finds that MDS does not exhibit the bias toward larger species seen with conventional DLS. In Figure 1b, DLS measurements overestimate the average size of the mixtures.

The authors note that the measurements using microfluidic diffusional sizing require a significantly lower amount of analyte with respect to DLS, in particular, for species with sizes equal to or smaller than a few nanometers, for which concentrations one order of magnitude higher relative to MDS are needed to generate a detectable scattering signal using DLS.

Microfluidic diffusion sizing in the direct detection of specific target species

Finally, microfluidic diffusion sizing is used for the direct detection of specific target species within a complex mixture in a quantitative manner, under native conditions, without the need for separation (as in a Western blot) or for immobilization on a surface (as in an ELISA). To do this the authors use a pre-labeled fluorescent nanobody against ɑ-synuclein, and observe a size change when incubated with an E. coli lysate in which ɑ-synuclein is expressed (Figure 2b)