Investigation of the Subcellular Localization of Zinc Phthalocyanines by Raman Mapping

Raman mapping has been used to determine the subcellular distribution of two substituted zinc phthalocyanines designed for use as photosensitizers in photodynamic therapy. Each compound was incubated over a range of time periods in two cultured cell lines, and the cells were subsequently formalin-fixed for analysis. Raman spectra were recorded at 1–2 μm steps across the cell, with the use of 782 nm laser excitation in order to minimize absorption by the photosensitizer chromophore and the consequent photodynamic activation of the system. Maps have been formed showing the distribution of the phthalocyanines within the cells. This distribution is seen to depend upon incubation time and the molecular structure of the phthalocyanine. Similar patterns of uptake are observed in both cell lines. Atomic force microscopy has been used to validate the technique used to correct the maps for variations in Raman sampling volume, resulting from inhomogenous cell thickness.