Merocyanine 540 adsorbed on polyethylenimine-functionalized graphene oxide nanocomposites as a turn-on fluorescent sensor for bovine serum albumin.

Graphene oxide (GO)-based fluorescence sensors are attractive and versatile tools for various sensing applications. Herein, we report the photophysical properties of merocyanine 540 (MC540) in an aqueous dispersion including graphene oxide (GO) and GO chemically functionalized with branched polyethylenimine (PEI), and the application of a novel designed MC540/PEI-GO system for BSA (bovine serum albumin) detection. Initially, the negatively charged GO surface was modified using PEI to form high positively charged PEI-GO nanocomposites via the amine groups of PEI. Later, to form MC540/PEI-GO system, MC540 molecules were assembled on PEI-GO nanocomposites having an attractive surface for negatively charged functional materials. The interaction of MC540 molecules with PEI-GO nanocomposites in aqueous dispersion led to a change in the photophysical properties of the dye. The variations in the photophysical properties of MC540 were spectroscopically characterized and explained. It was determined that the interaction of MC540 with GO sheets and PEI-GO nanocomposites strongly quenched the fluorescence of the dye. However, the quenching effect of the PEI-GO nanocomposites on the fluorescence of MC540 was specifically prevented by the addition of BSA, in which the fluorescence of MC540 was nearly recovered. By using the PEI-GO nanocomposites-based fluorescence platform, BSA has been detected with a LOD (limit of detection) of 7.45 nM, which is one of the best applications among BSA sensors to date. The designed sensor system was easily applied for the detection of BSA in commonly used biological media and clinical injectable fluids. Consequently, we suggest a simple, fast, sensitive and selective BSA sensor designed by assembling MC540 molecules on PEI-GO nanocomposites.