An unusual “off-on” fluorescence sensor for iron(III) detection based on fluorescein–reduced graphene oxide functionalized with polyethyleneimine.

Polyethyleneimine (PEI)–modified reduced graphene oxide (rGO) based fluorescent sensor is reported for metal-ion sensing. PEI–rGO nanocomposites are synthesized by a facile and controllable method using hydrazine hydrate as a main reducing agent and PEI that is a reducing agent, surface modifier and polymer host. The formation of PEI–rGO nanocomposites is confirmed with X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, UV–vis spectroscopy, Zeta potential measurements and Dynamic Light Scattering (DLS) analysis. Afterward, the interaction of fluorescein (FL) with PEI–rGO nanocomposites in aqueous dispersion, leading to the formation of FL/PEI–rGO ternary system, are studied at various conditions by using UV–vis absorption, steady-state and time-resolved fluorescence spectroscopies. It is observed that the photophysical properties of FL are dependent on the amount of both FL and PEI–rGO nanocomposites. The sensing ability of FL/PEI–rGO ternary system are examined in the detection of metal ions as a fluorescent sensor. The spectroscopic data reveal that the FL/PEI–rGO ternary system shows high sensitivity and selectivity for Fe 3+ ions in aqueous solution. The detection limit for Fe 3+ are determined to be 1.12 μM. [ABSTRACT FROM AUTHOR]