Enhanced Electrochemical\nDetection of Nonelectroactive\nCompounds Based on Surface Supramolecular Interactions on Chevron-like\nGraphene Nanoribbons Modified through Click Chemistry

In this study, we\nhave developed a nanostructured electrochemical\nsensor based on modified graphene nanoribbons tailored for the analysis\nof nonelectroactive compounds via a surface competitive assay. Stigmasterol,\na nonelectroactive phytosterol, was selected as a representative case.\nChevron-like graphene nanoribbons, chemically synthesized, were immobilized\nonto glassy carbon electrodes and covalently functionalized to allow\nthe on-surface formation of a supramolecular complex. To this end,\nthe nanoribbons were first modified through a diazotization process\nby electrochemical reduction of a 4-azidoaniline diazonium salt, leaving\nthe electrode surface with azide groups exposed to solution. Next,\nthe incorporation of a ferrocene group, as a redox probe, was carried\nout by a click chemistry reaction between ethynylferrocene and these\nazide groups. Finally, the recognition event leads to the formation\nof a supramolecular complex between ferrocene and a macrocyclic receptor\non the electrode surface. To this end, the receptors cucurbit[7]uril,\ncucurbit[8]uril, and β-cyclodextrin were evaluated, with the\nbetter results obtained with β-cyclodextrin. Atomic force microscopy\nand scanning electron microscopy measurements were performed for the\nmorphological characterization of the resulting electrochemical platform\nsurface. The ability of β-cyclodextrin to form an inclusion\ncomplex with ferrocene or with stigmasterol allows to perform a competitive\nassay, which translates into the decrease and recovery of the ferrocene\nelectrochemical signal. For stigmasterol determination, a linear concentration\nrange between 200 and 750 μM and a detection limit of 60 μM\nwere obtained, with relative errors and relative standard deviations\nless than 7.1 and 9.8%, respectively.