A Schiff base derivative used as sensor of copper through colorimetric and surface plasmon resonance techniques

• Low detection limit for copper of 1.25 × 10−7 M in aqueous media.
• Low colorimetric (naked eye) detection limit of 2 × 10−6 M in aqueous media.
• Sensing copper ions through the use of surface plasmon resonance (SPR) technique.

Organic molecular sensors have the advantage of being used through easy, fast, economical and reliable optical methods for detecting toxic metal ions in the environment. In this work, we present a simple but highly specific organic ligand 5-Chloro-2-[(1E,2E)-3-(4-(dimethylamino)phenyl)allylidene)amino)]phenol (S1) that works as a colorimetric sensor of copper ions in aqueous solutions. Binding interaction between S1 and various metal ions was established by UV–Vis spectroscopic measurements showing favorable coordination toward Cu2+ and practically no interference with the presence of other metal ions, i.e., Cd2+, Co2+, Cr2+, Fe3+, Mg2+, Ni2+, Hg2+, Pb2+, Mn2+, and Zn2+. S1 exhibited binding-induced color changes from yellow to pink with a detection limit of 1.25 × 10−7 M measured by spectroscopic methods, while colorimetric changes could be observed at naked eye for concentrations as low as 2 × 10−6 M. Furthermore, we also demonstrated that S1 can be useful for sensing copper ions through the use of surface plasmon resonance (SPR) technique. This technique allowed detecting the presence of Cu2+ in aqueous solutions at the concentration level of ca 1.5 × 10−6 M due to changes in the refractive index.

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