Flow-Induced Shift of the Donnan Equilibrium for Ultra-Sensitive Mass Transport Measurement Through a Single Nanochannel

TL;DR

This paper demonstrates how liquid flow perturbs the Donnan equilibrium inside a nanochannel, enabling ultra-sensitive measurement of mass transport by combining experimental fluorescence spectroscopy with advanced modeling.

Contribution

It introduces a novel approach to measure mass flow in nanochannels by analyzing flow-induced shifts in the Donnan equilibrium, supported by theoretical and numerical models.

Findings

Flow depletes the Donnan equilibrium under liquid flow.

The method achieves unprecedented flow rate sensitivity.

The approach is versatile for nanofluidic applications.

Abstract

Despite mass flow is arguably the most elementary transport associated to nanofluidics, its measurement still constitutes a significant bottleneck for the development of this promising field. Here, we investigate how a liquid flow perturbs the ubiquitous enrichment-or depletion-of a solute inside a single nanochannel. Using Fluorescence Correlation Spectroscopy to access the local solute concentration, we demonstrate that the initial enrichment-the so-called Donnan equilibrium-is depleted under flow thus revealing the underlying mass transport. Combining theoretical and numerical calculations beyond the classical 1D treatments of nanochannels, we rationalize quantitatively our observations and demonstrate unprecedented flow rate sensitivity. Because the present mass transport investigations are based on generic effects, we believe they can develop into a versatile approach for nanofluidics.