Hyperbranched polyethylenimine-based sensor of multiple metal ions (Cu2+, Co2+ and Fe2+): colorimetric sensing via coordination or AgNP formation. Issue 107 (16th October 2015) - Vinod Kumar, V.
Abstract : A commercially available HPEI polymer has been used as a single colorimetric probe for the selective colorimetric sensing of multiple metal ions in aqueous solution with distinguishable colors. Abstract : Hyperbranched polyethylenimine (HPEI), an amine rich polymer, has been used as a colorimetric probe for selective sensing of multiple metal ions (Cu 2+, Co 2+ and Fe 2+ ) with clearly distinguishable color in aqueous solution. The selective coordination of Cu 2+ with the chelating amines of HPEI induced a visible color change from colorless to blue across a wide pH range (pH 4.0 to 10.0). Other metal ions did not show any significant color change. Interestingly, the addition of Co 2+ and Fe 2+ into HPEI in the presence of silver ions (Ag + ) leads to the formation of strong yellow and brown colors, respectively. The control studies suggest that Co 2+ and Fe 2+ undergo oxidation and reduce the silver ions into silver nanoparticles (AgNPs). The strong surface plasmon resonance (SPR) vibration of the AgNPs was responsible for the yellow/brown color. UV-visible studies showed a strong absorption peak at 400 nm for Co 2+ and a broad absorption with λ max at 420 nm for Fe 2+ . HR-TEM studies confirmed more uniform spherical AgNPs for Co 2+ with HPEI–Ag + and polydisperse AgNP aggregates for Fe 2+ . The limit of detection of the HPEI probe for Cu 2+ is 0.25 μg L −1 and those of the HPEI–Ag + probe for Co 2+ and Fe 2+ are 40 and 30 μg L −1, respectively. The practical application of the HPEI probe for selective sensing of multiple metal ions with distinguishable colors has been demonstrated on Whatman filter paper. Thus, simple commercially available HPEI has been successfully used for the selective colorimetric sensing of biologically important Cu 2+, Co 2+ and Fe 2+ metal ions in aqueous medium.