Effect of Graphene and Graphene Oxide Dispersions in Poloxamer-407 on the Fluorescence of Riboflavin: A Comparative Study

The effect of graphene (G) and graphene oxide (GO) dispersions in a triblock copolymer, Kolliphor P407 (poloxamer-407), on the fluorescence of vitamin B-2 (riboflavin) has been comparatively investigated. The quality of the dispersions was assessed by measuring the thickness of their flakes and visualizing their distribution within the copolymer and degree of exfoliation via scanning and transmission electron microscopies (SEM and TEM). The influence of G or GO and copolymer concentration on the fluorescence intensity was studied, and fluorescence quenching phenomena were observed; these become more effective with increasing G or GO content for Kolliphor concentrations equal to or above the CMC, the diminution in intensity being stronger for G dispersions, which is related to the different hydrophobicity of the nanomaterials, because these modify the distribution equilibrium of the vitamin between the solution and the Kolliphor micellar aggregates. Further, for a given G or GO concentration, the intensity decreases with increasing copolymer concentration. The ratio between the fluorescence intensity in the absence and the presence of G fits to a second-order polynomial, suggesting a combined mechanism of static and dynamic quenching, while for GO dispersions it follows the Stern-Volmer linear, equation in the low concentration range. The quenching observed herein could be useful in the development of optical sensors for riboflavin determination. G-based sensors are expected to have better performance in terms of sensitivity and repeatability than GO-based ones due to their stronger nanomaterial-vitamin interaction, superior quenching efficiency, and higher signal-to-noise ratio.