Quantification of neomycin in rubella vaccine by off/on metal ion mediated photoluminescence from functionalized graphene quantum dots.

The determination of neomycin sulfate was made using photoluminescent amino-functionalized graphene quantum dots (obtained from hydro-exfoliation of a mixture of citric acid and glutathione). From the several ions tested, Fe³⁺ was the best mediator to enable an off/on photoluminescence effect used for quantification. The mediation of Fe³⁺ was found to be crucial as it is responsible for the photoluminescence quenching effect, due to the interaction with quantum dots surface, also having large affinity towards neomycin that removes Fe³⁺ from the surface of GQDs, consequently, promoting restoration of the original nanomaterial photoluminescence. Such signal restoration was proportional to the neomycin sulfate concentration added. The linearized analytical response covered three orders of magnitude (10^-7 to 10^-5 mol L^-1). The proposed method is an alternative to those requiring labor-intensive procedures for chemical the derivatization of neomycin (due to the lack of chromophore groups in aminoglycosides). The method was successfully tested in the analysis of rubella vaccine containing trace residues of neomycin and in pharmaceutical compositions containing neomycin sulfate after solid phase extraction using an aminoglycoside imprinted polymer to improve selectivity in determinations.