Electrochemical quartz crystal microbalance study of azurin adsorption onto an alkanethiol self-assembled monolayer on gold.
A quartz crystal microbalance coupled with electrochemistry was used to examine the adsorption of azurin on a gold electrode modified with a self-assembled monolayer of octanethiol. Azurin adsorbed irreversibly to form a densely packed monolayer. The rate of azurin adsorption was related to the bulk concentration of azurin in solution within the concentration range studied. At a high azurin concentration (2.75 muM), adsorption was rapid with a stable adsorption maximum attained in 2-3 min. At a lower azurin solution concentration (0.35 muM), the time to reach a stable adsorption maximum was approximately 30 min. Interestingly, the maximum surface concentration attained for all solution concentrations studied by the QCM method was 25 +/- 1 pmol cm-2, close to that predicted for monolayer coverage. The dissipation was monitored during adsorption, and only small changes were detected, implying a rigid adsorption model, as needed when using the Sauerbrey equation. Cyclic voltammetric data were consistent with a one-electron, surface-confined CuII/CuI azurin process with fast electron-transfer kinetics. The electroactive surface concentration calculated using voltammetry was 7 +/- 1 pmol cm-2. The differences between the QCM and voltammetrically determined surface coverage values reflect, predominantly, the different measurement methods but imply that all surface-confined azurin is not electrochemically active on the time scale of cyclic voltammetry.
School of Chemistry, Monash University, Clayton, Victoria 3800, Australia.
Barry D
BD
Fleming
Slavica
S
Praporski
Alan M
AM
Bond
Lisandra L
LL
Martin
D000327:Adsorption; D000465:Algorithms; D001400:Azurin / Q000737:chemistry*; D015374:Biosensing Techniques / Q000379:methods*; D003460:Crystallization; D004563:Electrochemistry; D004566:Electrodes; D006046:Gold / Q000737:chemistry*; D011791:Quartz / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013499:Surface Properties; D013997:Time Factors
D012996:Solutions; D013438:Sulfhydryl Compounds; D001400:Azurin; D011791:Quartz; D006046:Gold