Novel modified electrodes for sensing and protein electrochemistry

The research herein reports the characterization and development of a novel modified gold electrode consisting of gold nanoparticles attached to the end of a 11-amino-1-undecanethiol self-assembled monolayers (SAMs). Polycrystalline gold electrodes modified with a passivating SAM shows that the immobilization of nanoparticles on the SAM ‘switch on’ the electrochemistry. The electrical properties of this electrode-monolayer-nanoparticle system were further investigated. The onset of electrochemistry was not influenced by the size of nanoparticles with a range between 15 and 60 nm. Furthermore, the effect of the charge of gold nanoparticles was evaluated by grafting short chain alkanethiols on nanoparticles as it was hypothesized that the onset of electrochemistry was perhaps due to the redox species being adsorbed onto nanoparticles. However, the electrochemical reactivity was reestablished even with electrostatic charge repulsion between positively charged modified nanoparticles and ruthenium hexamine. Finally, the influence of the density of gold nanoparticles was investigated, showing that the coverage of nanoparticles is quite similar even though the electrochemical signal increases with the longer incubation between 10 seconds and 120 seconds. The investigation of protein electrochemistry by using horseradish peroxidase (HRP) immobilized on the electrode-monolayer-nanoparticle construct was reported. As the HRP immobilized on the nanoparticles, the electron transfer kinetics was faster than that of HRP on the SAM in the absence of particles. This indicated that the underlying construct of gold nanoparticles attached on SAMs has opened a conducting channel that facilitates electron transfer when HRP was immobilized on the gold nanoparticles. Furthermore, the electrochemistry of another approach upon covalent attachment of HRP on the nanoparticles was also examined, showing that the electron transfer rate was faster than that of the method for electrostatic binding of HRP on the surface of particles. This suggested that the immobilization of HRP by covalent attachment on this modified electrode has higher efficiency in electron transfer between the enzyme and the electrode