(Invited) Hydrogen Peroxide Electrochemical Sensing Based on a TiO2 nanotubes Electrode Modified with Hibiscus Sabdariffa L. Anthocyanins
Authors: Martinez-Pacheco Mariana , Lozada-Ramirez Jose Daniel , Cerro-Lopez Monica 
Published: February 2020

The antioxidant properties of the alcoholic extract obtained from the calix of Hibiscus sabdariffa L.
(H.s.), mostly referred in the literature as jamaica or rozelle, have been used in the present research to build an electrode with hydrogen peroxide sensing activity. This plant belongs to the malvaceae family and originates from tropical Africa but nowadays its cultivation spreads widely through Mexico, Central and South America and Southeast Asia1. The calyx of H.s. contains the most valuable nutritional components, that at the same time are responsible for the pigmentation (anthocyanins) and the quality of the flavor and its aroma (organic acids). Hence, the dried flower of jamaica has been used as a flavoring additive for soft drinks, as a significant source of fiber and as a tool to fight inflammatory processes2-3. As anthocyanins are widely consumed and cultivated in Latin America, gaining insights about further biological activities is of great interest.
The anthocyanins found in H.s.have a strong scavenging effect on reactive oxygen and free radicals2. Some studies about the two main anthocyanins present in H.s. (delphinidin and cyanidin) demonstrated that both, the oxidation and the antioxidant activity, break the same O–H bond4-5.
In addition, a widely used nanomaterial to build working electrodes is TiO2 nanotubes6, because they can be produced at low expense and have shown an excellent chemical stability in their anatase phase7. Furthermore, TiO2 nanotubes can be characterized by their effective electron transfer behavior and their high adsorptive property of organic compounds due to abundant active sites6.
Therefore, this research project presents the methodology and results of a highly sensitive and selective electrochemical system, composed only by a titanium dioxide nanostructured electrode functionalized with a purified extract of jamaica. This technique establishes a new method to detect and quantify hydroxyl radicals in solution with a quantification limit of 3.91x10-6 M and a detection limit of 2.39 x10-6 M, that also have proven to be selective against other radicals (ABTS). In combination with the low cost in manufacturing and the eco-friendly nature of the materials, the novel electrode provides a significant enhancement when compared with other sensing materials available nowadays.
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