Scanning Electrochemical Microscopy Studies of Glutathione-Modified Surfaces. An Erasable and Sensitive-to-Reactive Oxygen Species Surface

A surface sensitive to reactive oxygen species (ROS) was prepared by reduction of a diazonium salt on glassy carbon electrode followed by the chemical coupling of glutathione (GSH) playing the role of an antioxidant species. The presence of active GSH was characterized through spectroscopic studies and electrochemical analysis after labeling of the -SH group with ferrocene moieties. The specific reactivity of GSH vs ROS was evaluated with scanning electrochemical microscopy (SECM) using the reduction of O-2 to superoxide, O-2(center dot-), near the GSH-modified surface. Approach curves show a considerable decrease of the blocking properties of the layer due to reaction of the immobilized GSH with O-2(center dot-) and the passage of GSH to the glutathione disulfide (GSSG). The initial surface could be regenerated several times with no significant variations of its antioxidant capacity by simply using the biological system glutathione reductase (GR)/NADPH that reduces GSSG back to GSH. SECM imaging shows also the possibility of writing local and erasable micropattems on the GSH surface by production of O-2(center dot-) at the tip probe electrode.