Functionalized polypyrrole/sulfonated graphene nanocomposites: Improved biosensing platforms through aryl diazonium electrochemistry

A novel electrochemical approach aimed at developing biosensing platforms based on polypyrrole/sulfonated graphene nanocomposites is reported. Specifically, nanocomposite layers are deposited onto platinum electrodes through the electrochemical polymerization of pyrrole monomer in the presence of reduced graphene oxide bearing phenylsulfonyl groups. Thus, the functionalized graphene nanofiller acts as dopant and balances the positive charges on the polymer chains, leading to an enhancement of the polymer's electrical conductivity and concomitantly increasing the electrode surface area. The polypyrrole/graphene nanocomposite films are further modified with carboxyphenyl groups via electrochemical reduction of 4-carboxyphenyl diazonium tetrafluoroborate. Grafting carboxyphenyl functionalities serves a dual purpose: it permits the covalent immobilization of glucose oxidase via carbodiimide chemistry and also forms an electrode blocking layer which hinders the oxidation of interfering substances. The feasibility of this strategy is demonstrated by the preparation of a glucose biosensor which exhibited an improved performance: wide linear range (0.02-12 mM), good sensitivity (0.56 μA mM−1 cm−2) and adequate selectivity towards common interferents including ascorbic acid, paracetamol, uric acid, and cysteine.