Direct measurement of effective diffusion coefficients in nanochannels using steady-state dispersion effects

Abstract

We present a method to measure effective diffusion coefficients of fluorescently labeled molecules inside a nanofluidic system. Molecules with small diffusion coefficients show a larger lateral dispersion than highly diffusive species, which is counterintuitive. We performed measurements with wheat germ agglutinin proteins and obtained an effective diffusion coefficient which is four orders of magnitude lower than its free diffusion coefficient. Our technique which is a direct and relatively simple measurement of the effective diffusion coefficients inside nanochannels of well controlled dimensions could help fundamental studies in membranes and separation sciences.

Direct Observation of Transitions between Surface-Dominated and Bulk Diffusion Regimes in Nanochannels

“…Overall, these are the dominant contributions to an effective diffusion coefficient which is strongly decreased when measuring the diffusion of proteins in nano-confinements 9,12,24 . …”

Molecular Dynamics and Monte Carlo simulations resolve apparent diffusion rate differences for proteins confined in nanochannels

“…The ratio of the bulk diffusion constant to the MC-calculated diffusion constant in the nanochannel for three ionic concentrations which are the same as have been experimentally measured in Durand et al, 2009[28] For the Durand 2007 experiment the evaluated diffusion constant is the same order of magnitude as the experimentally measured value, ~10,000 times higher than the bulk diffusion constant. These results show that the qualitative and nanochannel [27] experiments can be matched with appropri fractional surface coverage of proteins, f surf , and the probability of surface interaction P surf which are both physically…”

“…[27,28] Assumed probability that a protein will interact with the surface, determined by the thickness of the EDL and protein surface concentration troute…”

“…In the first study, Durand et al measured diffusion coefficients for fluorescently-labelled wheat germ agglutinin (WGA) in nanochannels, and found an effective diffusion coefficient for confined molecules which is four orders of magnitude lower than its free diffusion coefficient. [27] In the second set of experiments, WGA molecules were observed by fluorescence correlation spectroscopy (FCS) in a nanochannel formed by two parallel borosilicate glass plates separated by 50 nm. [28] The FCS observation volume is well approximated by a right circular cylinder with radius 420 nm.…”

Effect of DNA Methylation on the Velocity of DNA Translocation through a Nanochannel

“…As described previously, larger DNA molecules with a lower diffusion coefficient can show lower lateral dispersion in the direction of the width and depth of a nanoslit, and this lateral dispersion can affect DNA translocation velocity in the direction of the length of the nanoslit. 12 The nanochannel used here was 300 nm wide × 300 nm high, and the DNA could freely diffuse in the directions of the width and the depth of the nanochannel.…”