Spectroscopic measurements of interactions between hydrophobic 1-pyrenebutyric acid and silver colloidal nanoparticles

Abstract

We compared the adsorption and desorption of 1-pyrenecarboxylic acid (PyC), 1-pyreneacetic acid (PyA), and 1-pyrenebutyric acid (PyB) on silver nanoparticles (AgNPs) via interfacial spectroscopic tools to study the role of the aliphatic units between pyrene and carboxylic group. The negative surface charges of AgNPs at ca. -51 mV shifted up to -11 mV, after adsorbing hydrophobic pyrene compounds. The three pyrene acid compounds appeared to adsorb onto AgNPs via their carboxylate units by referring to the observation of the broad v(COO-) bands at 1380-1410 cm(-1) in the Raman spectra. X-ray photoelectron spectroscopy (XPS) also supported the C-0 species in the C(1)s region. AgNPs were found to efficiently quench the fluorescence of the three pyrene acid adsorbates. The highest Stern-Volmer constant of PyA may be due to the largest overlap integral with the surface Plasmon absorption band of AgNPs. The butyric unit was expected to lead a stronger binding on Ag, as suggested by density functional theory (DFT) calculations. The adsorbed pyrene acid compounds appeared to be released from AgNPs by thiol-containing glutathione (GSH). PyB with the butyric group exhibited larger quenched fluorescence intensities and smaller released amounts than PyC and PyA in aqueous solutions and A549 cancer cells. Our study will be helpful in designing pyrene-based fluorescence sensors in cellular imaging.