Large scale Micro-Photometry for high resolution pH-characterization during electro-osmotic pumping and modular micro-swimming

TL;DR

This paper introduces a high-resolution micro-photometric method for monitoring pH gradients in microfluidic systems, enabling detailed analysis of electro-osmotic pumps and micro-swimmers with potential applications in modeling complex flow phenomena.

Contribution

The authors present a novel micro-photometric technique with 2 μm spatial resolution and 0.05 pH resolution, suitable for real-time pH gradient measurements in microfluidic applications.

Findings

Achieved 2 μm spatial resolution at video frame rate.

Demonstrated pH measurement accuracy of 0.05.

Validated method on electro-osmotic pump and micro-swimmers.

Abstract

Micro-fluidic pumps as well as artificial micro-swimmers are conveniently realized exploiting phoretic solvent flows based on local gradients of temperature, electrolyte concentration or pH. We here present a facile micro-photometric method for monitoring pH gradients and demonstrate its performance and scope on different experimental situations including an electro-osmotic pump and modular micro-swimmers assembled from ion exchange resin beads and polystyrene colloids. In combination with the present microscope and DSLR camera our method offers a 2 \mu m spatial resolution at video frame rate over a field of view of 3920x2602 \mu m^2. Under optimal conditions we achieve a pH-resolution of 0.05 with about equal contributions from statistical and systematical uncertainties. Our quantitative micro-photometric characterization of pH gradients which develop in time and reach out several mm is anticipated to provide valuable input for reliable modeling and simulations of a large variety of complex flow situations involving pH-gradients including artificial micro-swimmers, microfluidic pumping or even electro-convection.