Characterization of permselective coatings electrosynthesized on Pt–Ir from the three phenylenediamine isomers for biosensor applications

Abstract

The permeability of polymers, electrosynthesized at neutral pH on Pt–Ir cylinders from each of the three isomers of phenylenediamine ( oPD, mPD and pPD), to H 2O 2 (signal transduction molecule in many oxidase-based biosensors) and ascorbic acid (AA, archetypal interference species in biological applications of biosensors) was measured, and used to determine the permselectivity of the three polymers. P mPD was the coating with the greatest permselectivity for H 2O 2 over AA, for low concentrations of AA. For AA levels greater than 200 μM, however, poly- ortho-phenylenediamine (P oPD) was superior. Furthermore, stability studies indicated that the permselectivity of P mPD degraded rapidly, even after 1 day, supporting the choice of P oPD as the permselective membrane for biosensor implantation where AA levels are high, such as in brain monitoring. A variety of techniques were used to gain further insight into the PPD layers, specifically electrochemical quartz crystal microbalance, mass spectrometry and scanning electron microscopy. Together these studies indicate that P mPD forms the thickest layer (∼15 nm) and is the least soluble of the polymers, that the P oPD layer is ∼4 nm thick and may consist mostly of tetramers, while P pPD is the thinnest (∼3 nm) and appears to consist of trimers.