Time resolved luminescence of millisecond lifetime dyes in droplet microfluidic systems

Time-resolved luminescence enables high sensitivity measurements and determination of radiative lifetimes for a number of applications. The combination of time-resolved luminescence with droplet microfluidic systems creates a powerful combination of high sensitivity detection and multiplexing capabilities with high-throughput sampling. This study introduces a platform for time-resolved luminescence detection from a millisecond lifetime dye, CoraFluor-1-PFP (CRF-1), in microfluidic systems to further increase multiplexing applications. Optimized excitation and emission parameters were a 50 Hz (60% duty cycle) excitation cycle using a 340 nm LED combined with an 8 ms emission window. Using these parameters, the lifetime of CRF-1 was found to be 2.9 ms. These parameters were applied to a droplet microfluidic system where aqueous CRF-1 was dispersed into a fluorinated oil carrier phase. Droplet frequencies of 0.15, 0.85, and 1.85 Hz were evaluated by summation of the photon counts from each LED excitation cycle, revealing the droplet dynamics. Using this excitation and emission scheme, droplet rise times as short as 60 ms could be determined, indicating that even more rapid droplet frequencies are feasible. This platform advances time-resolved luminescence assays toward automated and high-throughput analysis.