The frequency response of QCM in electrochemically characterizing the immobilization on gold electrode

Since the detected molecule may probably attach to the uncovered surface, the coverage of the immobilized sensing film is very important for electrochemical biosensors. This is especially true for gold electrodes. One electrochemical quartz crystal microbalance (EQCM) approach is investigated for characterizing the coverage. A 5 MHz QCM element is used together with an electrochemical system. During the electrochemical experiments, the frequency response of the QCM is recorded simultaneously with the electrochemical parameters. Three cases, the bare, the 6-mecapto-1-hexanol modified and the 16-mer oligonucleotide probe (with a mercaptohexyl group at the 5′-phosphate end) modified gold electrodes are investigated. The results indicate that the frequency is more sensitive than the electrochemical response to the surface coverage. It could be used to evaluate the clearness of the electrode surface before immobilization, or the surface coverage after immobilization.