Imaging Free and Bound NADH Towards Cancer Tissue Detection Using FLIM System Based on SPAD Array

Abstract

Summary form only given. Single photon detectors allow us to work with the weakest signals such as auto-fluorescent biological sources. In combination with time gated operation mode, an array of detectors can be used as Fluorescence Lifetime Imaging system with extremely high sensitivity.Here we present fluorescence lifetime imaging using the `SwissSPAD' [1] sensor, an extensive 512-by-128pixel array of time-gated single photon avalanche diodes (SPADs). By taking a series of gated measurements and changing the gate delay, fluorescent lifetimes can be retrieved for each individual pixels. Over 65 thousand independent SPAD pixels creates a detailed spatial map of fluorescence lifetimes in the field of view of the sensor. In this work, we are presenting two milestones of our research. Firstly, we present proof of principle imaging lifetime measurements of Rhodamine B and Fluorescein, with lifetimes of 1.68ns and 4ns ns respectively, excited using a 532 nm 10 picosecond laser. Secondly, we show that using 266 nm excitation, we can distinguish between free(0.5ns) and bound(2.2ns) NADH using unlabelled auto-fluorescence. Freeand bound-NADH are known to be markers for the cancer tissues [2].