Palladium-Coated Submicron Electrospun Polymeric Fibers with Immobilized Uricase for Uric Acid Determination in Body Fluids

This work describes the development of a flexible uric acid (UA) biosensor based on palladium-coated submicrometer electrospun poly(methylmethacrylate) (PMMA) fibers metalized with gold and attached to polyethylene terephthalate substrate (Pd/Au/PMMA/PET). The morphological characterization conducted by scanning electron microscopy revealed nanoscale Pd dendritic structures. Electrochemical investigations in the absence and in the presence of redox probes demonstrated that these Pd nanostructures are responsible for a six-fold increase in the electroactive area and enhanced electron transfer kinetics when compared to the gold-coated electrospun fibers. The UA biosensor obtained by immobilizing the uricase enzyme (UrOx) onto the Pd/Au/PMMA/PET electrode surface, allowed UA detection with a sensitivity of 431 μA cm–2 mM–1 and a limit of detection of 12 μM. Investigation of the redox reactions of hydrogen peroxide (a product of the enzymatic oxidation of UA by UrOx) at the Pd/Au/PMMA/PET electrode demonstrated that the working principle of the biosensor is based on the reduction of PdO produced at the electrode surface during the spontaneous reduction of hydrogen peroxide on Pd. This allows a biosensor operating potential of −0.05 V (vs Ag/AgCl) with high selectivity. The UrOx/Pd/Au/PMMA/PET biosensor was applied for UA detection in body fluids (sweat, urine, and blood serum) with recovery values between 98 and 105%, which were validated by high-performance liquid chromatography analysis. The stability of the device was evaluated over a period of 3 months, retaining 78% of the initial sensitivity, and reproducibility with RSD = 4.9% was achieved. The analytical performance of the biosensor under harsh mechanical deformations and at physiological temperatures demonstrated the potential applications of the device to wearable sensing platforms.