Comparative electrochemical behavior of glucose oxidase covalently immobilized on mono-, di- and tetra-carboxylic acid functional Au-thiol SAMs via anhydride-derivatization route

Comparative electrochemical study of glucose oxidase (GOx) immobilized on gold electrodes modified by three types of mercaptocarboxylic acid self-assembled monolayers (SAMs), including 3-mercaptopropionic acid (MPA), 3-mercaptosuccinic acid (MSA), and thiodisuccinic acid (TDSA), is reported. GOx was immobilized on SAMs via anhydride route to prepare (Au-MPA-GOx), (Au-MSA-GOx), and (Au-TDSA-GOx) biosensors. Steps of formation and analytical performance of the prepared biosensors were traced by cyclic voltammetry (CV), chronoamperometry (CA), and electrochemical impedance spectroscopy (EIS). While partial surface coverage (θ) of gold by thiols showed the following order Au-MPA(θ = 36%) > Au-MSA(θ = 30%) > Au-TDSA(θ = 24%), inverse effect was observed for slopes (activities) of the calibration curves for glucose determination as Au-MPA-GOx < Au-MSA-GOx < Au-TDSA-GOx. This matter was explained based on advantages of multi-branch carboxylic acids (i.e. TDSA) allowing immobilization of more enzymes even with less surface coverage (24%) by thiols. Data obtained by CA and EIS methods for the entire of the study were in good agreement.