Immobilization of Pyrroloquinoline Quinone on Gold by Carbodiimide Coupling to Adsorbed Polyamines: Stability Comparison to Attachment via a Chemisorbed Thiol Monolayer

Pyrroloquinoline quinone (PQQ) was immobilized on gold electrodes by prior adsorption of the polyamines polyethylenimine, and triethylene tetraamine, followed by carbodiimide coupling of PQQ to the surface-adsorbed amine groups. The stability and electrochemical behavior of the electrodes, in which the amino-containing linker molecule is adsorbed on the electrode surface, were compared with those of electrodes prepared by carbodiimide coupling of PQQ to a cystamine monolayer, in which the sulfur-containing linker molecule is associated with the gold surface. The electrodes prepared using adsorbed polyethylenimine showed comparable stability to those based on a cystamine monolayer, but reveal enhanced stability to application of negative potentials (<-1.1 V). The method provides an alternative to the conventional functionalization of Au electrodes by thiols.