Rapid Electrochemical Detection of Levodopa using Polyaniline-Modified Screen-Printed Electrodes for the Improved Management of Parkinson's Disease

A portable test to rapidly determine levels of levodopa, the drug used to treat Parkinson’s disease, can improve clinical management of the disease. In this study, screen-printed electrodes were modified with polymers to facilitate the electrochemical detection of levodopa. Cyclic voltammetry was used to deposit a thin layer of polyaniline on the electrode surface. Scanning electron microscopy revealed high surface coverage, which did not impact the electrode's conductivity. Differential pulse voltammetry measurements with the polyaniline-modified electrodes enabled the measurement of levodopa at physiologically relevant concentrations with discrimination between a common interferent (ascorbic acid) and a structurally similar compound (L-tyrosine). However, the use of the polymer layer did not permit differentiation between levodopa and dopamine; the only difference in these molecules is that levodopa has an amino acid moiety whereas dopamine has a free amine group. Density functional theory calculations demonstrated that aniline formed a hydrogen bond between the amino group of the monomer and the meta-hydroxyl group, which is present in both levodopa and dopamine, with similar binding energies (-53.36 vs -50.08 kJ mol-1). Thus, the polymer-functionalised SPEs are a valuable tool to measure compounds important in Parkinson’s disease, but further refinement is needed to achieve selective detection.