Influence of buffer solution on structure and electrochemical properties of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) hydrogels

Numerous advantages of poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT-PSS) hydrogel make this material appropriable for biosensors developing. Among many of them, it may be exploited as an immobilization matrix for binding bioreceptors. Porous 3-D structure facilitates high loading of the enzyme and extends surface area, what results in better biosensor performance and signal increase. High water content generates hydrophilic environment, thus biocompatibility is greatly enhanced. Citrate or phosphate buffers are typically used to provide optimal pH for the immobilized enzyme. The present work reports on the development of the PEDOT-PSS hydrogels synthesized in phosphate buffer or citrate buffer solutions at pH = 5 to verify the influence of the anion present in the polymerization environment on the molecular structure and electrochemical properties of the hydrogel. The water content in each hydrogel sample is estimated by weighting the swelled and dried samples and termogravimetric analysis. It is shown that PEDOT-PSS obtained in phosphate buffer solution comprises much more water than hydrogel synthesized in citrate buffer. This property is of great importance for the electrocatalytic properties of immobilized horseradish peroxidase (HRP). Wherefore, the PEDOT-PSS/HRP modified electrode has been used for the amperometric detection of H2O2 at pH = 6. The phosphate containing ph-PEDOT-PSS/HRP biosensor is characterized by a good linear relation with the concentrations of H2O2 with a linear range from 0.0088 to 0.15 mM and from 0.4 to 10 mM and a low detection limit of 9.4.10(-7) M and 4.5.10(-5) M (S/N = 3), respectively. While the citrate containing cit-PEDOT-PSS/HRP sensor shows worse analytical parameters - linear range from 0.05 to 0.25 mM and detection limit of 1.10(-5) M (S/N = 3).