Novel silver nanoparticles decorated hybrid active film for the electrochemical determination of cysteine enantiomers.

BACKGROUND: Cysteine is a semi-essential amino acid, with l-cysteine being the predominant form in the human body. Recently, d-cysteine has been identified as an endogenous molecule, and its role in cancer development is linked to hydrogen sulfide synthesis. Monitoring cysteine enantiomers could aid in cancer screening and treatment evaluation. Although several analytical techniques are available, they often involve complex, expensive, and time-consuming procedures. Electrochemical methods offer a promising alternative due to their sensitivity, simplicity, and potential for point-of-care use. This work addresses the need for a reliable electrochemical sensor for the analysis of cysteine enantiomers.

RESULTS: A screen-printed carbon electrode was developed for the sensitive recognition and determination of cysteine enantiomers from whole blood samples from healthy individuals and cancer patients. The electrode features a novel nanomaterial composed of silver nanoparticles and a hybrid active film formed by electrodeposition of Sunset Yellow and l-methionine. Its surface morphology and electrochemical behavior were characterized using scanning electron microscopy, square wave voltammetry, cyclic voltammetry, and electrochemical impedance spectroscopy. Under optimized conditions, the current intensity ratio of l-cysteine to d-cysteine (Il/Id) was determined to be 1.31. The electrode demonstrated a wide dynamic range from 0.001 to 100.0 μmol L-1 and a low detection limit of 0.33 nmol L-1 for both enantiomers. It also allowed reliable analysis of enantiomeric ratios in non-racemic mixtures. The electrode's performance was validated in biological samples. Its construction involves a simple, one-step electrodeposition process, supporting its reproducibility and practical applicability in early disease screening.

SIGNIFICANCE: This work introduces a novel hybrid active film decorated with silver nanoparticles modified electrode that enables rapid, reproducible, sensitive, and enantioselective cysteine enantiomer determination within wide dynamic ranges and nanomolar limits of detection. Its excellent performance for enantiomer discrimination-validated in both non-racemic mixtures and real biological samples-confirms its practical application. These characteristics emphasize its significant potential for inclusion into diagnostic platforms focused on early disease screening, particularly in cancer diagnostics.