A calibration approach for the rapid estimation of fluorophore excited-state lifetimes with applications in biomedicine*

Nanosecond-pulse-width lasers, such as nitrogen lasers, are relatively inexpensive and are commonly used for biological and biomedical applications. Because the laser pulse width is comparable to fluorophore excited-state lifetimes ($\sim $1 -- 10 ns), deconvolution of the temporal system response is needed for accurate lifetime determination. Such deconvolution analysis can be time consuming, and so we report a method for rapid lifetime estimation based on geometric features of the time-resolved emission signal. We find that the time-integrated signal, normalized to the peak intensity, is linear with the lifetime, and can be used for calibration of the measured emission signal to the excited-state lifetime. The approach is accurate to $\sim $15{\%} despite using emission signals with low signal-to-noise ratios ($\sim $10). The approach has applications ranging from flow cytometry to fluorescence lifetime imaging microscopy. Results from fluorescence-based pH sensing are presented.