Effect of the polymerization bath on structure and electrochemical properties of polyaniline-poly(styrene sulfonate) hydrogels

- PANI-PSS hydrogels synthesized at pH = 0 and pH = 5 differ by: content of phosphate ions, phenazine oligomers and morphology.
- Presence of phosphate ions within the hydrogel influences the ion-exchange properties.
- Linear phenazine oligomers improve the time of response of the immobilized enzyme.

Conducting polymer hydrogels combine the mechanical and swelling properties of hydrogels with the specific electron transport and redox properties of conducting polymers. Such hydrogels are typically obtained by oxidative polymerization of the monomer at high concentration in the presence of a polyanion, which acts as a electrostatic cross-linking agent. In this contribution, we study polyaniline-poly(styrene sulfonate) (PANI/PSS) hydrogels synthesized in 1 M HCl (PANI/PSS/pH 0) or in phosphate solution at pH = 5 (PANI/PSS/pH 5). The composition of the polymerization bath influences the electrochemical properties of the hydrogel. Cyclic voltammetry responses of PANI/PSS/pH 0 studied at pH = 6 show a single redox pair with large potential distance (0.59 V) between the anodic and the cathodic peak. The distance between peaks for PANI/PSS/pH 5 is much smaller (0.15 V). Cyclic voltammetry results are correlated with vibrational spectra of hydrogels. Both PANI/PSS/pH 0 and PANI/PSS/pH 5 were tested as supports for horseradish peroxidase (HRP). The amperometric responses to H2O2 were immediate in the case of the enzyme immobilized in PANI-PSS/pH 5, while the enzyme immobilized in PANI/PSS/pH 0 exhibited a much slower response. The differences are explained by various ion-exchange properties of the two hydrogels and presence of phenazine oligomers in PANI/PSS/pH 5. The sensitivities of the enzyme immobilized in the two hydrogels were similar at 0.184 μA cm− 2 μM− 1 and 0.148 μA cm− 2 μM− 1 for PANI/PSS/pH 0 and PANI/PSS/pH 5, respectively. The limit of detection for HRP in PANI/PSS/pH 5 was equal to 76 nM. The limit of detection value was worse (0.9 μM) due to larger current noise value.

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