Microfluidic Pumping by Micromolar Salt Concentrations

TL;DR

This paper introduces an ion-exchange-resin-based microfluidic pump that uses trace ions to generate sustained fluid flows, revealing that minimal charge carriers can produce significant flows and informing future low-fuel microfluidic pump designs.

Contribution

The study demonstrates a novel microfluidic pump driven by micromolar salt concentrations, combining experimental, theoretical, and numerical methods to understand its operation.

Findings

Operates in nearly deionized water for over 24 hours

Induces fluid flows of micrometers per second over hundreds of micrometers

Flow decay follows a power-law characteristic of 2D and 3D flows

Abstract

An ion-exchange-resin-based microfluidic pump is introduced that utilizes trace amounts of ions to generate fluid flows. We show experimentally that our pump operates in almost deionized water for periods exceeding 24h and induces fluid flows of um/s over hundreds of um. This flow displays a far-field, power-law decay which is characteristic of two-dimensional (2D) flow when the system is strongly confined and of three-dimensional (3D) flow when it is not. Using theory and numerical calculations we demonstrate that our observations are consistent with electroosmotic pumping driven by umol/L ion concentrations in the sample cell that serve as 'fuel' to the pump. Our study thus reveals that trace amounts of charge carriers can produce surprisingly strong fluid flows; an insight that should benefit the design of a new class of microfluidic pumps that operate at very low fuel concentrations.