Ultrafast microfluidic drop sorter Mulholland, Brendan; Da Costa, Daniel; Eldridge, Dale
This project sought to design, implement and test a high-throughput fluorescence measurement system capable of measuring the fluorescence of picolitre-volume aqueous droplets. Additionally, it is desired to sort these droplets into one of two populations based on the measured fluorescent intensity each individual droplet. While full implementation of this last objective was placed outside the scope of this project, research was conducted in order to direct future work. Ultimately, the system is intended to become a versatile tool that will be useful for a wide variety of applications in biology and biochemistry. An optical system capable of measuring fluorescent emission from two distinct fluorescent dyes (specifically, fluorescein and Quasar 670, or equivalent) was designed. Optical and mechanical components were specified, sourced and ordered. LabVIEW software was developed to preview and record data collected from the system. MATLAB scripts were written to perform analysis of this data. A microfluidic droplet sorting device described in a 2010 PNAS publication by Agresti et al. was replicated. Droplet-generating microfluidic devices were designed, fabricated and demonstrated to function as expected. Measurement sensitivity (particularly to fluorescein), speed and robustness were identified as the critical indicators of system performance, and have been investigated in detail. The sensitivity limit was determined to lie in the range 10 – 30 nM, the system was verified to be capable of measuring droplet fluorescence at droplets flow rates of at least 649 droplets per second and the system was demonstrated to make and record fluorescent measurement data continuously for almost 4 hours. In order to physically sort droplets, it was determined that a high-voltage (~1kV), high-speed (1-20kHz) amplification circuit was required. Research was conducted into the feasibility of constructing a custom amplification circuit. It was determined that, while possible, this is a non-trivial design task which would require significant expertise and time commitment. Alternatives were investigated and it was determined that suitable commercial solutions are readily available, with the lowest end models starting at approximately $3000.
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