Electrochemical Assay to Quantify the Hydroxyl Radical Scavenging Activity of Medicinal Plant Extracts

Abstract

A new electrochemical assay has been developed which is based on quantifying the attack of OH. radicals on a selfassembled thiol monolayer on electrodes in the presence and absence of antioxidants. The OH . radicals were produced in Fenton solutions. The radical scavengers diminish the concentration of the OH . radicals in the Fenton solution, and the extent of thiol layer destruction is monitored with the help of a redox probe in solution, the signal of which is only generated at SAM-free electrode surface. The results of the electrochemical assay were compared with those of the standard DPPH . assay. In case of each plant extract, an excellent linear correlation was observed between the radical scavenging activity and the concentration of plant extracts; however, the scavenging properties of different plants strongly differ in the electrochemical and the DPPH . assay. Since the proposed new method probes the reactivity of radical scavengers towards OH . , one of the most important reactive oxygen radicals in tissues, it is supposed to provide much more relevant information than the DPPH . or other assays.

Poly(methylene blue)-modified electrode for indirect electrochemical sensing of OH radicals and radical scavengers

“…This pro-oxidative capacity of ascorbic acid is in accordance with previous results reported in literature (Berger et al 1997, Carr and Frei 1999, Valko et al 2005. However, in the few studies related to chemically modified electrodes (CMes) for OH · sensing (Gualandi et al 2014, Gualandi and Tonelli 2013, Scholz et al 2007, Hilgemann et al 2010, it is the first time that such behavior is observed concerning this pro-oxidative effect of AA when it is used as an antioxidant. Thus, in these cases, low AA levels should be maintained.…”

“…Thus, in these cases, low AA levels should be maintained. Such behavior could explain why a 100% OH radical scavenging was not reached in our previous work even when AA levels were systematically enhanced (Hilgemann et al 2010). Consequently, a 100% of OH radical scavenging effect cannot be reached.…”

“…The OH radical scavenging capacities were calculated according to the equation (1) (Hilgemann et al 2010):…”

“…In this sense, electrochemical assays are promising tools: suitable for fast analyses, based on inexpensive instrumentation and with simple operation protocols (Prieto-Simón et al 2008). Additionally, studies propose the use of chemically modified electrodes (CMEs) as a simple electrochemical approach to sense ROS and radical scavengers, with DNA, selfassembled monolayers of thiols, polyphenol films, and conducting polymers (CPs) (Scholz et al 2007, Liu et al 2005, Mello et al 2006, Hilgemann et al 2010, Wu et al 2012, Gualandi and Tonelli 2013, Gualandi et al 2014 as electrode modifiers. The ROS may attack the CME and the extent of the modifier destruction can be evaluated directly (in this case, when an electroactive layer is monitored) or using an electrochemical probe in solution (when a non-electroactive layer is used).…”

A Polypyrrole Based Sensor for the Electrochemical Detection of OH Radicals

“…A simple electroanalytical approach, based on the attack of chemically modified electrodes (CMEs) by oxygen radicals, has been proposed in the literature. DNA, polyphenol films or self assembled monolayers of alkylthiols were used as modifiers 8–12. The CME was dipped in a solution where the radicals were generated.…”