Fluorescence lifetime imaging of water-soluble porphyrin in human nasopharyngeal cells under two-photon excitation

Abstract

A comparative study of the two-photon absorption and emission properties of two free-based porphyrins (H2TMPyP and H2TPPS) and their zinc(II) complexes (ZnTMPyP and ZnTPPS) in three polar solvents has been carried out. The presence of the central zinc(II) ion leads to smaller two-photon absorption cross sections (δTPA), while the introduction of methylpyridinium substituents (N•+–CH3) results in larger ones. The δTPA values of H2TMPyP and ZnTMPyP are affected by both the solvent polarity and the hydrogen bonding between porphyrin and solvent molecules. In this work, the strongest two-photon fluorescence is given by H2TMPyP, which may efficiently get into four kinds of nasopharyngeal cell lines (NP69, SUNE1, CNE2, and CNE1) and prefer to localize in the nucleus. Two-photon fluorescence lifetime images of all the cell lines treated with H2TMPyP consist of a short- (τ1) and a long-lived component (τ2). The τ2 distribution of normal cell line NP69 shows one peak lifetime (∼2.12 ns), while those of the cancerous cell lines (SUNE1, CNE2, and CNE1) have two peak lifetimes (∼2.14 and ∼3.77 ns). The τ1 distribution around 0.68 ns is higher for the well differentiated nasopharyngeal cancerous cell line CNE1 compared with the poorly differentiated ones (SUNE1 and CNE2).