Organic nanoparticles of anion-based fluorophore 8-anilino-1-naphthalenesulfonate (ANS): Effects of ion-association and post-dilution

Abstract

On the basis of a modified ion-association method, fluorescent organic nanoparticles of 8-anilino-1-naphthalenesulfonate (ANS) are synthesized in pure aqueous solution. The ANS dye is an anionic chromophore having a strongly hydrophilic sulfonate group, so the use of bulky, bis-quaternary phosphonium co-cation, that is, o-xylylenebis(triphenylphosphonium) cation (XTPP), is very effective for producing ion-based nanoparticles with a diameter of 150–250 nm. Binding of ANS with XTPP significantly modulates the intensity and peak position of the dye fluorescence, but interestingly, the emission properties are strongly influenced by post-dilution of the native dispersions. Electron microscopy and dynamic light scattering experiments reveal that, upon post-dilution, native ANS nanoparticles are etched, and the size-reduced particles are interconnected with each other to form a particle network of about ∼200 nm, resulting in a remarkable change in the dye fluorescence.