Development of Cyanine 813@Imidazole-Based Doped Supported Devices for Divalent Metal Ions Detection

A NIR cyanine@imidazole derivative Cy1 was synthesized and evaluated as a metal ion sensor in solution. Cy1 was shown to be very sensitive to all metal ions tested, presenting a blue shift in the absorption from 668 nm to 633 nm, followed by a change in colour from pale green to blue with Zn2+, Cd2+, Co2+, Ni2+ and Hg2+ ions. Despite the blue shift in the absorption, a decrease at 633 nm (with a colour change from pale green to colourless), as well as a quenching in the emission intensity at 785 nm were observed for Cu2+ ions. The results show the formation of sandwich complexes of two ligands per metal ion with the highest association constant observed for Cu2+ (Log K-ass.abs = 14.76 +/- 0.09; Log K-ass.emis. = 14.79 +/- 0.06). The minimal detectable amounts were found to be 31 nM and 37 nM, with a naked eye detection of 2.9 ppm and 2.1 ppm for Hg2+ and Cu2+ ions, respectively. These results prompted us to explore the applicability of Cy1 by its combination with nanomaterials. Thus, Cy1@ doped MNs and Cy1@ doped PMMA nanoparticles were synthesized. Both nanosystems were shown to be very sensitive to Cu2+ ions in water, allowing a naked-eye detection of at least 1 ppm for Cy1@ doped MNs and 7 ppm for Cy1@ doped PMMA. This colourimetric response is an easy and inexpensive way to assess the presence of metals in aqueous media with no need for further instrumentation.

Automated summary

A new metal ion sensor was synthesized, which showed sensitive reactions to different metal ions and exhibited visible color changes. The sensor combined with nanomaterials also demonstrated high sensitivity in detecting Cu2+ ions in water.