Small molecules as fluorescent materials in bioimaging by two-photon absorption microscopy

Abstract

Upon irradiation with light, molecules can absorb photons to reach an electronic excited state, among several paths to go back to their ground state, molecules can emit light in a process called fluorescence. There are molecules that can simultaneously absorb two low energy photons from an infrared laser beam and combine their energies to access an electronic excited state that can emit photons of higher energy. This process has led to multiphoton fluorescence microscopy which is strongly dependent of the intensity of light and thus can create high resolution images, has deeper penetration and causes less damage to the cells and tissues compared to one-photon fluorescence microscopy. The technique is well established and uses fluorescence microscopes equipped with an infrared laser (700-1000 nm) and specialized commercial fluorophores and has been used to develop a wide variety of cellular imaging of organelles, DNA, enzymes, metal ions and reactive molecules [1]. However, there is still a need to obtain molecules that show higher fluorescence quantum yield, higher multiphoton absorption cross section, photostability, appreciable water solubility, high specificity towards the target analyte and low cytotoxicity. This work aims to show the progress and challenges in the development of materials for two-photon microscopy based on analysis of the scientific literature published to the date