RETRACTED: Studies on interactions of thionine with gold nanoparticles (Retracted article. See vol 317, pg. 768, 2008)

The interactions of thionine with gold nanoparticles have been studied by using UV-vis absorption spectroscopy, fluorescence spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. With addition of small amounts of gold nanoparticles, the absorption peak intensity of monomers of thionine decreases significantly, whereas that of H-type dimers of thionine increases. With further addition of gold nanoparticles, both the absorption peak intensities of the monomers and dimers of thionine increase, and the increasing magnitude of the peak intensity of the dimers is larger than that of monomers. The addition of gold nanoparticles makes the equilibrium between the monomer and H-type dimer forms of thionine move toward the dimer forms. Due to the binding between thionine and gold nanoparticles, the fluorescence quenching of thionine by gold nanoparticles is enhanced with increasing amounts of gold nanoparticles, and the quenching is both static and dynamic. TEM images show that the addition of thionine results in the formation of gold clusters, and further support the spectral results. Infrared spectroscopic studies show that the nitrogen atoms of both the NH2 moieties of thionine strongly bind to the gold nanoparticle surfaces through the electrostatic interaction of thionine with gold nanoparticles. For 3-6 nm particles, the number of adsorbed thionine molecules per gold particle is about 1.21 x 10(3). Thionine molecules can not only bind to a particle to form a compact monolayer via both the NH2 moieties of thionine, but also bind to two particles via their two NH2 moieties, respectively. (c) 2006 Elsevier B.V. All rights reserved.