Green and efficient determination of ʟ-dopa in complex polypill formulations using a magnetic microplate

A high-throughput and selective method for the determination of ʟ-dopa (levodopa) in complex formulations was developed. The method is based on the oxidation of ʟ-dopa to yield dopachrome using tyrosinase-labeled magnetic nanoparticles (TYR-MNPs) as the oxidation catalyst. TYR-MNP activity was retained at 75% after 20 reuse cycles, which is superior to previously reported systems that employ other substrates or cross-linkers for the immobilization of tyrosinase. In addition, the precision (< 3%), accuracy (recovery = 95–102%), and selectivity of the newly developed quantitative-analysis method for ʟ-dopa in complex polypill formulations meets the pharmaceutical industry’s quality-control requirements; consequently this method can be applied to the routine analysis of complex formulations. The quality-control assay uses 96-well microplates, which reduces the required volume of reagents, and the tyrosinase can easily be recycled and reused using an in-house-prepared magnetic microplate, thereby rendering the proposed method economical and less wasteful than existing methods.