Electrochemical characterization of in situ functionalized gold p-aminothiophenol self-assembled monolayer with 4-formylphenylboronic acid for recognition of sugars

The surface of a gold (Au) electrode was modified with p-aminothiophenol (p-ATP) and well-packed monomolecular layers through a sulfur–Au bond were formed. Functionalization of Au–ATP self-assembled monolayer (SAM) with 4-formylphenylboronic acid (BA) via Schiff's base formation, through in situ method, to fabricate Au–ATP–BA electrode is presented. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were used to investigate the changes in electrode behavior after each assembly step. The surface pKa value of the Au–ATP–BA SAM electrode was estimated by CV and EIS. In the presence of sugar, the terminal groups of Au–ATP–BA SAM electrode can react with sugar by forming the phenylboronate esters of sugar on the surface of the electrode; the pKa values for the Au–ATP–BA SAM electrode in the presence of different sugars (D-glucose, D-fructose, and D-mannose) were obtained. The fabricated electrode can be used as a novel biosensor for determining sugars on the basis of the change in ip of the Fe(CN)63−/4− ion in the presence of sugars. The biosensor exhibited excellent performance in determining D-glucose, D-fructose, and D-mannose, with low detection limits, wide linear ranges and good sensitivities.