Imaging natural fluorescence of the endogenous molecules is of clinical importance. Amino acids like Phenylalanine, Tyrosine and Tryptophan, structural proteins like collagen and elastin, and coenzymes directly involved in cellular metabolism like Nicotinamide Adenine Dinucleotide Phosphate (NAD(P)H) and Flavin Adenine Dinucleotide (FAD). Each endogenous molecule absorbs and emits at different wavelengths and has been used to detect various cancer including prostate cancer (PCa), based on fluorescence intensity. NAD(P)H and FAD provide detectable natural autofluorescence signals to monitor metabolic flux. Among listed amino acids, tryptophan (Trp) provides the strongest fluorescence signals. It has been shown by biochemical methods that degradation or reduction in the abundance of the Trp indicates the presence of cancer in biological systems. The one-photon absorption of Trp is 260 nm which is phototoxic to the cells. The emission of Trp is 300-400 nm. Most of the optical microscopy system transmits maximally starting from 400 nm. To meet the Trp requirement, we configured the Zeiss 780 to provide maximum emission signal about 80% at 340 nm at the ND output port for three-photon excitation. The spectral sensitivity of the detector used for Trp imaging is 300-650 nm which is integrated with the Zeiss780 system. A ROI-based segmented cell FLIRR assays was developed to investigate the interaction between NAD(P)H and Trp.
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