Time-gated fluorescence spectroscopy and imaging of porphyrins and phthalocyanines

Time-gated fluorescence spectroscopy provides a very useful tool to evaluate the photophysical properties and the incorporation mechanisms of drugs interacting with biological substrates. In particular, taking into account that different fluorophores, even if overlapped in fluorescence spectrum, present different fluorescence lifetimes, it is possible to evidence the emission of a single molecular species by choosing a suitable observation window in the time domain. Using this technique, the effect of systemic administration on the uptake of Hematoporphyrin Derivative (HpD), its tumor localizing fraction (TLF), and disulphonated Aluminum Phthalocyanine (AlS2Pc) at the cellular level was evaluated on a murine ascitic tumor. The results obtained indicate that the TLF is the part of HpD actually retained by the cells and that AlS2Pc is incorporated more rapidly with respect to porphyrins. The observation of the gated spectra of HpD also evidenced the possibility of improving the contrast between the fluorescence of the cells and that of the drug. Thus, an imaging system has been developed which utilizes a gated, intensified, CCD camera synchronized with a subnanosecond laser- pulse excitation. The gate can be set to a minimum width of 5 ns and arbitrarily delayed with respect to the laser pulse. By optimization of the gate parameters, porphyrin fluorescence images in single cells and microscopy sections of tumor were obtained with a valuable signal- to-noise ratio.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.