We initially tested the electrochemical activity of beta-carotene and lutein at unmodified glassy carbon electrodes. We found good sensitivity (1 nA/μM) at high, micromolar concentrations, but serum levels are at nanomolar concentrations. To enhance the electrochemical activity, we modified the sensor surface with β-cyclodextrin, which has a hydrophobic core. Our goal was that the beta-carotene will be attracted to the β-cyclodextrin core, increasing surface interaction and sensitivity. Instead we saw a decrease in electrochemical activity. Further investigation with a methylene blue mediator indicated two results. First, it is unlikely the beta-carotene strongly interacts with the β-cyclodextrin surface. And, second, the presence of a co-solvent or surfactant can greatly disrupt the surface β-cyclodextrin activity.
