Salen Derivatives Functionalized CdSe-ZnS Quantum Dots as Fluorescent Probes for Selective Cu(II) and Fe(II) Sensing

The surface of luminescent semiconductor quantum dots CdSe-ZnS was successfully grafted with multidentate ligand, Salen, to give quantum dot-Salen through condensation reaction between surface amine and salicylic aldehyde. This hybrid material possesses the characteristics of stable and narrow photoluminescence at similar to 610 nm in water and organic polar solvents. It exhibits selective metal sensing toward certain transition metals such as Fe(II) and Cu(II) by photoluminescence quenching with estimated limit of detection of about 30 mu M and 25 mu M, repectively. The selective sensing of ferrous ions could be attributed to the fluorescence energy transfer between the quantum dots and the surface ferrous Salen complexes because the absorption spectra of the surface metal complexes overlap with the emission wavelength of the quantum dots. On the other hand, the selective sensing of copper can be attributed to both the fluorescence energy transfer and surface adsorption mechanism, but the latter quenching path is dominant which is supported by the fluorescence quenchig behavior.