Oxidative and Stepwise Grafting of Dopamine Inner-Sphere Redox Couple onto Electrode Material: Electron Transfer Activation of Dopamine

Abstract

The immobilization of dopamine, a neurotransmitter, onto macroelectrode and microelectrode surfaces has been performed following two strategies. The first consists of a one-step grafting based on electrochemical oxidation of an amino group in acidic media. The second is a stepwise process starting with electrochemical grafting of diazonium, leading to the attachment of aryl layer bearing an acidic headgroup, followed by chemical coupling leading to immobilized dopamine molecules onto the electrode surface. Electrochemical, infrared (IR) spectroscopy, and X-ray photoelectron spectroscopy (XPS) analyses evidence that both methods are suitable for the immobilization of dopamine onto millimetric and micronic electrodes. The electrochemical responses of modified electrodes demonstrate that the electroactivity of the attached dopamine layer appears unaffected by the nature of the spacer, alkyl or aryl layers, suggesting that the communication, through tunneling, between the attached dopamine and the electrode is possible. More interestingly, the dopamine-modified electrode exhibits electron transfer activation toward dopamine in solution. As a result, not only does the dopamine modified electrode yield a fast electron transfer with lower ΔE(p) (30 mV) than the majority of pretreatment procedures but also the ΔE(p) is as small as that observed for more complex surface treatments.