Liquid-core waveguide TCSPC sensor for high-accuracy fluorescence lifetime analysis

Liquid-core waveguide (LCW) has many advantages such as the elimination of optical artifacts typically exhibited in systems employing lenses and filters. However, due to the effect of temporal dispersion, LCWs are typically employed in steady-state fluorescence detection microsystems rather than in fluorescence lifetime measurement (FLM) systems. In this paper, we present a compact liquid-core waveguide time-correlated single-photon counting (LCW-TCSPC) sensor for FLM. The propagation of excitation within the LCW is analyzed both analytically and in simulations, with results in agreement with experimental characterization. Results reveal an optimal region within the LCW for highly accurate FLM. The proposed prototype achieves excellent excitation rejection and low temporal dispersion as a result of optimization of the propagation length of the excitation within the LCW. The prototype achieves a detection limit of 5 nM for Coumarin 6 in dimethyl sulfoxide with < 3% lifetime error. The techniques proposed for analyzing the LCW for TCSPC based FLM and prototype demonstration pave the way for developing high-performance fluorescence lifetime measurement for microfluidics and point-of-care applications.