Effective Rapid\nFluorescence Lifetime Imaging of the\nBrain: A Novel Approach Using Upconversion Photoluminescence Lifetime\nBased on Gate-Width Acquisition

The rapid lifetime imaging of upconversion photoluminescence\nis\nbecoming increasingly popular in biosensing, anticounterfeiting, optical\nthermometry, and multiplex imaging. However, existing Rapid Lifetime\nDetermination (RLD) techniques are limited in their ability to integrate\ncontiguous, overlapping, and discrete windows into a single measurement,\nhindering accurate fluorescence lifetime retrieval. This study introduces\na new data acquisition method using three adjustable gates in a single\nmeasurement to enhance resolution. We apply this method in rapid upconversion\nfluorescence lifetime imaging to visualize capillary networks and\nmap pH levels based on intensity and lifetime differences in mouse\nbrain vasculature. By enhancing brightness using NaYbF4@NaYF4,Er,Tm@NaYF4\nnanoparticles, we achieve effective brain imaging. Monte Carlo simulations\ndemonstrate a relative standard deviation of less than 0.4% for fluorescence\ndurations spanning from 1 to 20 ns. This method provides a fast, high-contrast\nsolution for multiplex brain imaging, addressing the limitations of\nslow data collection and poor accuracy in existing RLD techniques.