Central composite design-empowered colorimetric detection of levodopa by nanozyme based on tartaric acid-iridium nanoparticles: Towards visual assay by a pink color palette.

BACKGROUND

Levodopa (L-DOPA) is a well-tolerated dopamine replacement agent and the gold standard drug in the treatment of Parkinson's disease (PD). Due to the importance of controlling concentration levels of L-DOPA for better treatment management, the fabrication of a visual sensor for naked-eye monitoring of this drug in human biofluids as a home kit is highly demanded. This study introduces novel and highly advanced nanostructures based on tartaric acid (TA) stabilized iridium (Ir), denoted as TA-IrNPs, which serve as a mimetic laccase for oxidizing L-DOPA.

RESULTS

The catalytic oxidation of L-DOPA using the TA-IrNPs nanozyme, followed by the interaction of the oxidation product with 4-aminoantipyrine (4-AAP) in a mildly acidic medium, provides a high-performance methodology for developing a spectroscopic and RGB-based colorimetric sensor. This sensor readily detects L-DOPA through a color-tunability approach, underscoring the importance of colorimetric technique as a primary means of data acquisition in this research. The colorimetric response is pivotal in quantifying L-DOPA levels, as it yields observable color changes that correlate with concentration levels. For a targeted assay, the assay condition before the analysis has been simulated by optimizing some key effective variables in the sensing process using the central composite design (CCD) approach. Adding different concentrations of L-DOPA from 0.60 μM to 65.93 μM to the proposed nanozyme in the presence of 4-AAP under the optimum conditions presents an absorbance peak at 516 nm with pink color tonalities. This behavior differs from the optical behavior of the L-DOPA in the presence of nanozyme or 4-AAP individually.

SIGNIFICANCE

The resulting obvious color tonality as the pink color palette makes fingerprint patterns, which are the traceable naked eye for the sensitive assay of L-DOPA. The proposed spectroscopic and RGB-based methodology, which involves non-invasive and visual analysis of L-DOPA in some pharmaceutical tablets and human biofluids as real samples using eco-friendly reagents, has been well evaluated according to the international criteria of green chemistry principles.