Novel Fluorescent Near-Infrared Agent for Biomedical Applications

Abstract

Squaraines represent a class of organic dyes operating in red and near-infrared regions. Due to their unique optical characteristics, such as high extinction coefficients, reduced background fluorescence and light scattering, photostability, these fluorophores attract ever-growing attention as prospective bioimaging agents. The present contribution overviews the spectral properties and some biological applications of the novel squaraine dye SQ-1. This probe was found to possess very high lipid-associating ability manifesting itself in a sharp increase of its emission. Binding of SQ-1 to the lipid bilayers containing zwitterionic and anionic lipids was found to be controlled mainly by hydrophobic interactions. Analysis of SQ-1 spectral behavior in the model membrane systems containing heme proteins revealed the dye sensitivity to the reactive oxygen species. This effect was supposed to originate from the reaction between lipid radicals and SQ-1 occuring at the squaric moiety or in its vicinity. Resonance energy transfer studies highlight the applicability of SQ-1 to structural characterization of amyloid fibrils.