A water-soluble, cationic bis-porphyrin exhibiting a more sensitive fluorescent response to Cu2+ relative to its monomeric counterpart

A water-soluble, cationic bis-porphyrin (Bis-TMPipEOPP) was synthesized, characterized, and its optical properties were investigated. Its fluorescence was found to be specifically quenched by paramagnetic Cu2+ ions via a static quenching mechanism. Based on these findings, an organic solvent-free sensing platform was developed for the “turn-off” detection of Cu2+. Such a platform could achieve sensitive Cu2+ quantitation at a detection limit of 8.8 nM. Compared to its monomeric counterpart TMPipEOPP, Bis-TMPipEOPP exhibited a higher tendency to self-aggregate due to the synergy between the two porphine rings. This characteristics conferred the proposed Bis-TMPipEOPP-based Cu2+-sensing platform with a sensitive fluorescent response to low concentrations of Cu2+ in a linear detection range of between 10 nM and 300 nM. However, the TMPipEOPP-based method provided observable changes in the fluorescent signal only at Cu2+ concentrations >200 nM. These results potentially offer a method for improving the performance of fluorescent-dye-based Cu2+ sensors.