Abstract
Natural methylxanthines, caffeine, theophylline and theobromine, are widespread biologically active alkaloids in human nutrition, found mainly in beverages (coffee, tea, cocoa, energy drinks, etc.). Their detection is thus of extreme importance, and many studies are devoted to this topic. During the last decade, graphene oxide (GO) and reduced graphene oxide (RGO) gained popularity as constituents of sensors (chemical, electrochemical and biosensors) for methylxanthines. The main advantages of GO and RGO with respect to graphene are the easiness and cheapness of synthesis, the notable higher solubility in polar solvents (water, among others), and the higher reactivity towards these targets (mainly due to π–π interactions); one of the main disadvantages is the lower electrical conductivity, especially when using them in electrochemical sensors. Nonetheless, their use in sensors is becoming more and more common, with the obtainment of very good results in terms of selectivity and sensitivity (up to 5.4 × 10−10 mol L−1 and 1.8 × 10−9 mol L−1 for caffeine and theophylline, respectively). Moreover, the ability of GO to protect DNA and RNA from enzymatic digestion renders it one of the best candidates for biosensors based on these nucleic acids. This is an up-to-date review of the use of GO and RGO in sensors.
Highlights
Graphene oxide (GO) is a nanostructured material formed by graphite sheets in which some of the aromatic C=C double bonds are oxidized, introducing oxygen atoms and giving rise to different functional groups
Due to the noteworthy importance of graphene and graphene oxide as nanomaterials in various application fields, a very high number of papers regarding their production can be found in the literature along with reviews [1,2,3], to which we refer with respect to syntheses and applications
Yue and coworkers [64] reported the use of a glassy carbon electrode modified with a Fe2 O3, reduced graphene oxide (RGO) and PEDOT composite for caffeine detection (Table 4, entry 7)
Summary
Graphene oxide (GO) is a nanostructured material formed by graphite sheets (graphene) in which some of the aromatic C=C double bonds are oxidized, introducing oxygen atoms and giving rise to different functional groups (epoxides, alcohols, carboxylic acids). Yue and coworkers [64] reported the use of a glassy carbon electrode modified with a Fe2 O3 , RGO and PEDOT composite for caffeine detection (Table 4, entry 7) This modified electrode gave very good results in terms of electrocatalytic effect, reproducibility and long-term stability, making it possible to reach a 3.3 × 10−7 mol L−1 caffeine detection limit with a very good linear interval. A pyrolytic graphite (PG) electrode was modified with ERGO and silver nanoparticles (AgNPs) in order to have a huge electrocatalytic effect, so that the detection limit for caffeine reached the value of 5.4 × 10−10 mol L−1 , maintaining a very large interval of linearity (Table 4, entry 8) The application of this electrochemical sensor to biological samples (i.e., in the presence of interferents) gave good results. In this figure, is the current intensity of caffeine signal higher for ERGO modified electrode, and the potential is less positive
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