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This work describes the development of a novel biosensor for determination of dopamine) DA) in the presence of H 2 O 2 and folic acid, and uric acid as interferences. The biosensor was fabricated from a carbon paste electrode modified with electrostatically immobilized hemoglobin (Hb) on copper oxide (CuO) nanoparticles and multi-walled carbon nanotubes. Because some phenolic compound biosensors were developed using the peroxidase properties of hemoglobin, this cane cause the reduction of phenolics in the presence of H 2 O 2 . However, the presence of hemoglobin in this electrode led to catalytic oxidation of DA at the electrode surface in the presence of H 2 O 2 . The biosensor's performance for phenolic compound detection depends on Hb acting as an electron mediator. This biosensor presents a sensitive response for DA. The parameters of the electrode fabrication with experimental conditions for Hb immobilization on CuO nanoparticles were optimized. Linearity for the detection of the DA was observed from 5 μM to 1 mM. Its detection limit was calculated at ∼20 nM. Electrode response reached 80% of its primary response after 30 days. The response time of the developed electrode was about 10 seconds.

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This work describes the first report about the simultaneous determination of levodopa (L-DOPA) with folic acid (FA) and uric acid (UA) based on electrocatalytic oxidation of L-DOPA with peroxidase properties of hemoglobin (Hb) in the presence of H2O2 as Hb activator. Bovine Hb was electrostatically immobilized on WO3 nanoparticles (WO3NPs) in pH between Hb and WO3NP isoelectric points, and subsequently, a carbon paste electrode (CPE) was modified with the obtained WO3NPs-Hb and multiwalled carbon nanotubes (MWCNTs). The resulting biosensor supplied a sensitive and suitably stable biosensor for the simultaneous determination of L-DOPA, UA, and FA. The obtained linear range and detection limit for L-DOPA, UA, and FA were completely acceptable, and the biosensor response time for these molecules was relatively short so that it reaches about 95 % of its maximum response in less than 10 s. The applicability of the current biosensor was confirmed with the determination of L-DOPA in the presence of fixed amounts of FA and UA in some real samples by the standard addition method.