Characterization of a Squaraine/Chitosan System for Photodynamic Therapy of Cancer

Abstract

In this work, a squaraine dye CS5 was characterized and evaluated for its potential in photodynamic therapy. The studies were performed in ethanol and also in a powdered biopolymer, in this case chitosan. Ground state absorption, absolute fluorescence quantum yields, fluorescence lifetimes, and transient absorption were determined in order to evaluate the advantage of adsorbing the dye onto a biopolymer. Several concentrations of the dye, adsorbed onto chitosan, were prepared in order to evaluate the concentration effect on the photophysical parameters under study. A remarkable increase in the fluorescence quantum yield and lifetimes was detected when compared with the dye in solution. Also, a very clear dependence of the fluorescence quantum yield on the concentration range was found. A lifetime distribution analysis of these systems fluorescence evidenced the entrapment of the dye onto the chitosan environment with a monoexponential decay which corresponds to the monomer emission in slightly different environments. The transient absorption spectrum was obtained without sensitization indicating the existence of a triplet state which takes special importance in the generation of phototoxic species namely singlet oxygen. The subcellular localization of a photosensitizer is critical for efficient photoinduced cell death, in this way, colocalization studies were performed within HeLa cell line (human cervical carcinoma) through confocal microscopy. Toxicity in the dark and phototoxicity of CS5 were also evaluated for the same cellular model.

Spectroscopic Analysis of Parathyroid and Thyroid Tissues by Ground-State diffuse Reflectance and Laser Induced Luminescence: a Preliminary Report

“…The signals were collected by a collimating beam probe coupled to an optical bre (fused silica) in this way assuring the connection to the monochromator entrance. The re ectance R is obtained for each sample and the remission function is calculated with the equation Further details of the use of this absorption spectroscopic technique can be found in [9][10][11][12] The absorption spectra of parathyroid, thyroid and fatty tissue from human subjects have been acquired in the range between 200 nm and 800 nm with the use of this technique.…”

“…Laser sources with wavelengths of 650 nm and 785 nm were used to excite the sample. The acquisition setups are fully described in [9][10][11][12].…”

Synthesis, Photochemical and In Vitro Cytotoxic Evaluation of New Iodinated Aminosquaraines as Potential Sensitizers for Photodynamic Therapy

“…As a consequence, structural modification of squaraine dyes become a very active area of research. Though a considerable number of different squaraine compounds has been developed envisioning their use as PDT sensitizers, both the in vitro and in vivo evaluation of their photodynamic capacity has been poorly addressed [20,21,22,23,24,25,26,27,28,29,30,31,32,33,34].…”

Synthesis, photochemical and in vitro cytotoxic evaluation of benzoselenazole-based aminosquaraines

“…Even though a significant number of different squaraine compounds have been tailored to be used as PDT photosensitizers, both the in vitro and in vivo assessment of their photodynamic action have been poorly explored. [24][25][26][27][28][29][30][31][32][33][34][35][36][37] Aminosquaraines, a particular class of cationic squaraine dyes bearing an amino group replacing one of the oxygen atoms of the central squaric ring, have previously shown to be able to produce singlet oxygen in variable quantum yields depending on the nature of the amino substituents and the degree of halogenation of both the terminal nuclei and the amino group. 21,23,38,39 The ability of aminosquaraines to generate singlet oxygen is generally much superior to that of the non-functionalized zwiterionic analogues 39 and is thought to arise from a higher degree of rigidification of the dye's structure due to the presence of a bulkier group and to possible intramolecular hydrogen bonding.…”