Stable and low impedance anti-fouling coating formed from the reductive adsorption of aryl diazonium salts on electrode surfaces

Abstract

This thesis has presented the research work towards developing the stable low impedance anti-fouling interface, for improving the in vitro and in vivo performance of electrochemical biosensors and implanted electrodes. Aryl diazonium salt reductive adsorption, a versatile surface functionalization approach offering robust surface chemistry, was chosen to fabricate gold and glassy carbon surfaces for the interface construction.

A detailed comparison of the aryl diazonium salt chemistry between on gold and on glassy carbon was conducted. The results suggest the grafted phenyl derivatives are much less electrochemical stable on gold than on glassy carbon. The cause of electrochemical instability of phenyl layers on gold was speculated to be the greater orbital mixing between the layers and the electrode surface on gold than on glassy carbon. Therefore, the zwitterionic interface construction was continued on glassy carbon surfaces only. Two zwitterionic surfaces, which respectively consisted of single component phenyl layers presenting phosphorylcholine groups and mixed phenyl layers presenting sulfonate and trimethylammonio groups, were both successfully produced. The detailed study of the mixed phenyl layers formation has revealed the intermolecular interaction between the two aryl diazonium salts in the solution. This interaction has played important role in affecting the potentials of reducing aryl diazonium salts and the surface composition of the mixed layers.

The evaluations of protein resistance have shown the two zwitterionic phenyl layers on glassy carbon are both as effective as alkanethiol SAMs presenting OEG (oligo ethylene glycol) groups on gold at resisting different charged proteins. The phenyl layers presenting OEG groups on glassy carbon, which were prepared for comparison, exhibited generally much less protein resistance than OEG-SAM. The impedance measurements have shown the two zwitterionic phenyl layers have significantly lower impedance than OEG phenyl layers. The phenyl derivatives based zwitterionic surfaces have presented desired anti-fouling features with low impedance and long-term stability.