Getting Enhanced Catalytic Surfaces for Catechol Sensing! Combination of Grafted Aryldiazonium Derivative and Either Cross-Linking Dopamine or Coupling Tyrosinase Immobilizations

The research work presented here describes the development of catalytic surfaces immobilizing dopamine via cross-linking or tyrosinase via covalent bond on an electrografted screen-printed carbon electrode with a 4-nitrobenzenediazonium ion. A simple electrochemical reduction approach was used to graft aryldiazonium ions onto commercial electrodes, resulting in the formation of a covalently bonded aromatic layer on the electrode surface. After functionalization with aminophenyl groups, dopamine, an important neurotransmitter, was immobilized by imine bond formation using glutaraldehyde as a bifunctional cross-linking molecule. The presence of immobilized dopamine was confirmed by cyclic voltammetry following the electrochemical response of the hydroquinone/quinone redox process from catechol functionalities on the surface, which are responsible for the catalytic activity. In addition, the surface was also characterized by cyclic voltammetry using the redox probe, [Fe(CN)6]3-/4-, obtaining a signal on this catalytic DA-biosensor about 14 times higher than that of a bare electrode, achieving a dynamic concentration range spanning three orders of magnitude. Remarkable sensitivity was also obtained by combining the electrografting, in situ diazotation to generate grafted aryl diazonium ions on the surface and coupling reaction to anchor the tyrosinase enzyme to the electrode surface. The response of the TYR-biosensor towards catechol, using the redox probe as mediator, was 10 times higher than that obtained with the dopamine modified catalytic surface. These modified surfaces offer promising alternatives for the voltammetric quantification of catechol in environmental fields.