Detection of Cationic Phenolic Derivatives at a Surfactant-Doped Screen-Printed Electrode for the Sensitive Indirect Determination of Alkaline Phosphatase
Résumé
The enzyme-label alkaline phosphatase (AP) commonly used in immunoassay was recently detected at subfemtomolar concentration with a screen-printed electrode (SPE) coated with a Nation film (O. Bagel et al., Anal. Chem., 1997, 69, 4688-4694) through the catalytic transformation of an anionic substrate (aromatic monoester phosphate) to a cationic electroactive product P+ (phenol substituted by a cationic function). In order to improve the technique, a new cation-exchanger-doped SPE was developed and its analytical performances were evaluated with several cationic phenolic products. The doped SPEs were prepared from a carbon ink loaded with the sodium salt of dodecylbenzene sulfonic acid. The anionic surfactant was strongly retained within the dry ink and it allowed the accumulation of nanomolar concentrations of cationic phenol derivatives to occur through an ion-exchange process at the electrode surface. The accumulated phenol compounds were detected by the voltammetric oxidation of their phenolic function. Preliminary results obtained with AP (detection limit of ca. 10-14 M) appear promising for enzyme immunoassays.