A naphthoquinone/SAM-mediated biosensor for olive oil polyphenol content

• Self-assembly of mercaptopropyl naphthoquinone on gold electrode surface.
• Phenol oxidation using quinone-mediated tyrosinase.
• Sensitive detection of sub-micromolar levels of phenol.
• Phenol detection at moderate cathodic potentials (∼−0.35 V vs. Ag/AgCl) using chronoamperometry.
• Determination of phenols in Tunisian virgin olive oil.

We report on the design of an amperometric tyrosinase-based biosensor using a self-assembled monolayer of ω-mercaptopropyl naphthoquinone on gold electrode as an electron mediator. Under optimal conditions (i.e. pH = 7.4 and E = −0.35 V vs. KCl), the chronoamperometric response of the naphthoquinone-modified bioelectrode to successive additions of phenol was evaluated. The biosensor exhibits sensitive bioelectrocatalytic response at a working potential of −0.35 V vs. Ag/AgCl (sat.KCl), reaching the steady-state current within 40 s after each addition of phenol solution with a range of 0–135 μM and a limit of detection and quantification which are 0.019 μM and 0.0633 μM, respectively. The bioelectrode was used to determine the content in polyphenol in a local virgin olive oil.