Low electro-synthesis potentials improve permselectivity of polymerized natural phenols in biosensor applications

First-generation amperometric biosensors are often based on the electro-oxidation of oxidase-generated H₂O₂. At the applied potential used in most studies, other molecules such as ascorbic acid or dopamine can be oxidized. Phenylenediamines are commonly used to avoid this problem: when these compounds are electro-deposited onto the transducer surface in the form of poly-phenylenediamine, a highly selective membrane is formed. Although there is no evidence of toxicity of the resulting polymer, phenylenediamine monomers are considered carcinogenic. An aim of this work was to evaluate the suitability of natural phenols as non-toxic alternatives to the ortho isomer of phenylenediamine. Electrosynthesis over Pt-Ir electrodes of 2-methoxy phenols (guaiacol, eugenol and isoeugenol), and hydroxylated biphenyls (dehydrodieugenol and magnolol) was achieved. The potentials used in the present study are significantly lower than values commonly applied during electro-polymerization. Polymers were obtained by means of constant potential amperometry, instead of cyclic voltammetry, in order to achieve multiple polymerizations, hence decreasing the time of realization and variability. Permselective properties of natural phenols were significantly improved at low polymerization potentials. Among the tested compounds, isoeugenol and magnolol, polymerized respectively at +25mV and +170mV against Ag/AgCl reference electrode, proved as permselective as poly-ortho-phenylenediamine and may be considered as effective polymeric alternatives. The natural phenol-coated electrodes were stable and responsive throughout 14 days. A biosensor prototype based on acetylcholine esterase and choline oxidase was electro-coated with poly-magnolol in order to evaluate the interference-rejecting properties of the electrosynthesized film in an amperometric biosensor; a moderate decrease in ascorbic acid rejection was observed during in vitro calibration of biosensors.