Photoluminescence of oligomers of aniline-2-sulfonic acid formed in the presence of AuCl4- and sodium citrate: Application in the optical detection of hemoglobin

Interaction of AuCl4- with monomers like aniline, ethylene dioxythiophene, pyrrole, etc., results in the formation of Au nanoparticle supported conducting polymers. In a recent work, Au supported polyethylene dioxythiophenes (PEDOTs) were used as catalyst for the homogeneous chemical reduction of nitrophenol to aminophenol. The polymerization of aniline sulfonic acid leads to the formation of soluble oligomers. Co-polymerization of aniline monomer with sulfonated counterpart is expected to enhance the processing ability of the resulting conducting co-polymer. In this work, we report the effect of two reducing agents namely aniline-2-sulfonic acid and sodium citrate on the reduction of AuCl4-. The chemical reduction of AuCl4- in the presence of the two reducing agents results in the formation of Au clusters as characterized by UV-vis spectra, transmission electron microscopy and MALDI-TOF measurements. The chemical reaction monitored as a function of time using UV-vis spectral measurements provides evidence for the formation of oligomers. The formation of Au along with fluorescent oligomers of aniline-2-sulfonic acid in the presence of sodium citrate was characterized with photoluminescence spectra. The phenomena of luminescence quenching in the presence of hemoglobin were used for the determination of hemoglobin at 10 nM level. The commonly occurring interfering bio-molecules (up to 5 micromolar levels) like ascorbic acid, uric acid, dopamine, glutathione and glucose indicate no significant interference. (C) 2014 Elsevier B.V. All rights reserved.