Luminescent and absorptive metal-coated emulsions for micro-velocimetry

TL;DR

This paper introduces silver-coated oil droplets that are luminescent and absorptive, serving as novel tracers for microfluidic velocity measurements, demonstrating their effectiveness in flow profiling within microchannels.

Contribution

The work presents a new type of metal-coated emulsion tracer with tunable density and optical properties for microfluidic velocimetry, expanding beyond traditional fluorescent beads.

Findings

Successfully synthesized luminescent, absorptive silver-coated droplets

Demonstrated accurate velocity profiling in microchannels

Results comparable to standard polystyrene tracers

Abstract

Fluorescent latex beads have been widely used as tracers in microfluidics over for the last decades. They have the advantages to be density matched with water and to be easily localizable using fluorescence microscopy. We have recently synthesized silver-coated oil droplets that are both luminescent and absorptive, by first coating the oil interface with a polydopamine layer and then depositing a silver layer by a redox process. They have a mean diameter of 6 \mu m and a their density has been matched to the density of water by adjusting the thickness of the metallic layer. In this work we used these particles as tracers to measure the velocity profile of a water flow in a PDMS microchannel with a rectangular cross-section, which allowed us to confirm the predictions of the Stokes equation with results comparable to those of common submicronic polystyrene particles.