Electropolymerized hydrophobic polyazulene as solid-contacts in potassium-selective electrodes

Electropolymerized hydrophobic polyazulene (PAz) based solid-state potassium ion-selective electrodes (SC-ISEs) have been characterized in terms of their suitability for clinical application. Polarization of the PAz solid contact before applying the plasticised poly(vinyl chloride) based K+-selective membrane was implemented as a convenient approach to address the general problem of the irreproducible standard potential (E-0) of SC-ISEs. Using this method, the E-0 reproducibility among different electrodes was, in the worst case, +/- 7.9 mV (n = 4). The effectiveness of the redox buffer-free approach presented here in stabilizing E0 is strengthened by the absence of light, oxygen and carbon dioxide sensitivity of the PAz SC-ISEs. No evidence was found for the formation of an aqueous layer for the PAz-based SC-ISEs. Thus the hydrophobic carbon structure of PAz having a water contact angle of 98 +/- 11 degrees, which is slightly higher than that for graphene, can apparently efficiently counteract the aqueous layer formation. In terms of the specific application, the PAz solid contact ISEs were found to show a remarkably good potential stability at their first contact with an aqueous sample. We also confirmed that the PAz-based SC-ISEs can be used for the accurate determination of the K+ concentration in serum solutions. Overall, the PAz solid contact shows significant advantages as compared to the state-of-the-art of electrically conducting polymer based SC-ISEs.