Dual fluorescence ratiometric technique for micromixing characterization

• Published in: Experiments in fluids Vol. 59; no. 11; pp. 1 - 15
• Main Authors: Bedding, David C., Hidrovo, Carlos H.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.11.2018; Springer Nature B.V
• Subjects: Emission; Engineering; Engineering Fluid Dynamics; Engineering Thermodynamics; Excitation; Fluid- and Aerodynamics; Fluorescence; Heat and Mass Transfer; Image processing; Laser applications; Micromixing; Parallel flow; Research Article; Serpentine; Variation
• ISSN: 0723-4864; 1432-1114
• DOI: 10.1007/s00348-018-2618-9

To probe high-speed mixing within microfluidic devices, an imaging technique that uses fluorescent emissions as an indicator of fluorophore concentration has been developed. Given that fluorescent emission varies linearly with excitation intensity, higher powered excitation sources, such as lasers, must be used to collect sufficient emission information over short periods of time. However, since laser-based excitation sources tend to be spatially and temporally non-homogeneous, a ratiometric imaging technique is used to correct these fluctuations without removing concentration information. Image processing is used to determine the homogeneity of the ratio values and, by correlation to the concentration, the level of mixing for the whole sample can be determined. The accuracy of this technique is assessed by comparing experimental results to a parallel flow micromixer COMSOL simulation of the actual concentration and overlaying imaging results. The dual fluorescence ratiometric technique is accurate within 11% of the simulations. The technique is then used to characterize a serpentine droplet micromixer which uses chaotic advection to increase the rate of mixing throughout the sample. This system is characterized using four different oil flow rates for mixing measurements taken for three different height locations throughout the channel. Graphical abstract