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Abstract: A novel fluorescein derivative, synthesized by the reaction of fluorescein hydrazide and 1-phenyl-3-methyl-4-benzoyl-5-pyrazolone, was evaluated as a chemoselective metal ion sensor. Addition of Cu2+ to an aqueous solution of the fluorescein derivative resulted in a rapid color change from colorless to deep yellow together with a distinctive change in UV–vis absorption spectrum. However, other common alkali-, alkaline earth-, transition- and rare earth metal ions induced no or minimal spectral changes. The stoichiometry of the reaction and association constant of the fluorescein derivative with Cu2+ are described. Experimental results indicate that the fluorescein derivative could provide a rapid, selective and sensitive response to Cu2+, and could be used as a potential Cu2+ colorimetric chemosensor in aqueous solution. [ABSTRACT FROM AUTHOR]

Herein Pd/Fe 3 O 4 -PEI-RGO nanohybrid was synthesized by dispersion of Pd NPs and Fe 3 O 4 NPs on PEI modified graphene oxide sheets. This nanohybrid was found to possess superior peroxidase-like activity, and could efficiently oxidize 3,3′,5,5′-Tetramethylbenzidine (TMB) by hydrogen peroxide (H 2 O 2 ) to produce a color reaction. Therefore, this provides a sensing platform for the colorimetric detection of H 2 O 2 in solution. The linear range for H 2 O 2 was from 0.5 to 150 μM and the limit of detection was as low as 0.1 μM. Moreover, the nanohybrids have the advantages of facile preservation and rapid separation. More importantly, comparing with the other catalysts (PEI-RGO, Fe 3 O 4 -PEI-RGO and Pd-PEI-RGO), this nanohybrid exhibits the enhanced peroxidase catalytic activity. Thus, it is expected that this nanohybrid could conveniently and efficiently detect H 2 O 2 in the pharmaceutical, environmental and industrial fields. [ABSTRACT FROM AUTHOR]