Highly fluorescent graphene oxide-poly(vinyl alcohol) hybrid: an effective material for specific Au3+ ion sensors.

We have developed a new highly fluorescent graphene oxide (GO)/poly(vinyl alcohol) (PVA) hybrid (GO-PVA) in an acidic medium (pH 4). Fourier transform infrared (FTIR) spectra indicate the formation of hydrogen bonds between the hydroxy group of PVA and the hydroxy groups of GO. The hybrid is highly fluorescent, because of passivation by hydrogen bonding, as evident from Raman spectra. The quantum yields of GO-PVA hybrids are higher than that of GO. The fluorescent microscopic images of the hybrids exhibit a fibrillar morphology, and all of them emit highly intense green light. Field-emission scanning electron microscopy (FESEM) micrographs also show a fibrillar morphology, which is produced due to the supramolecular organization of GO-PVA complex. The highly fluorescent GO-PVA1 hybrid has been used as a fascinating tool for selective sensing of Au(3+) ions in aqueous media with a detectable limit of ~275 ppb. The sensitivity of the Au(3+) ion (300 μM) in the presence of 600 μM concentrations of each ion (Cu(2+), Ag(+), Mg(2+), Ca(2+), Zn(2+), K(+), Pb(2+), Co(2+), Ni(2+), Pd(2+), Fe(2+), Fe(3+), and Cr(3+)), taken together, is unique, exhibiting a quenching efficiency of 76%. The quenching efficiency in the presence of a biologically analogous mixture (d-glucose, d-lysine, BSA, Na(+), K(+), Ca(2+), Mg(2+), Zn(2+)) (600 μM each) is 73%, which suggests that the GO-PVA1 hybrid is an efficient sensor of Au(3+) ions. The average lifetime of GO at pH 4 increases in the GO-PVA1 hybrid, indicating the formation of a more stable excited state but the increase in lifetime value after addition of Au(3+) salt solution to the hybrid solution indicates dynamic quenching. The selectivity of sensing of Au(3+) is attributed to its reduction potential being higher than that of other metal ions and XPS data of GO-PVA1 hybrid with 300 μM Au(3+) substantiate the reduction of Au(3+) to Au(0), because of the transfer of excitons from the hybrid facilitating the selective photoluminescence (PL) quenching.