ZnO-Porphyrin Composite Nanostructures as Discriminating Adducts for Metallic Ions in Aqueous Matrices

Tetrapyrrolic macrocycles are largely used in the sensing of vari-ous analytes both in liquid and in gaseous phase, but thestrong electronic delocalization of this class of molecules makesdifficult to realize a selective active layer. To overcome thisproblem, in the present work it is proposed the synthesis of asupramolecular adduct of zinc oxide nanostructure and a free-base tetra- pyridyl substituted porphyrin. The electronic struc-ture of the two organic/inorganic compounds allows to ob-serve a surface-enhanced Raman scattering (SERS) of the por-phyrin vibrational bands. This phenom enon is quenched by thepresence of mercuric and cupric ions according to two differentmechanisms monitored and explained by means of time re-solved fluorescence spectroscopy. It was demonstrated thatother substances in complex matrices, such as the food ex-tracts, do not affect the electronic communication betweenZnO and porphyrin preserving the SERS effect and minimizingthe effect of interfering compounds.