Chiral electrochemical sensing of propranolol enantiomers on D/L-Cys modified gold nanoparticles

•Both enantiomers of cysteine tested as surface bound diastereoisomeric selectors in chiral electrochemical sensing.•Unexpected change in electrochemical enantioselectivity upon the exchange of the surface-bound chiral selector's antipode is recorded.•Dual chiral systems are not a straightforward solution for enantioselectivity enhancement.•Normalized peak current ratios showed better enantiodiscrimination of propranolol compared to the raw peak potential/current changes.•Important differences in the heterogeneous electron transfer rate constant on the l-cysteine modified electrode were observed after the adsorption of propranolol enantiomers. The present study aims to explore the interaction mechanisms between propranolol (PRNL) enantiomers and bare and L/D-Cysteine modified gold nanoparticles (L/D-Cys−AuNPs) surfaces, using electrochemical (cyclic voltammetry, differential pulse voltammetry, electrochemical impedance spectroscopy) and microcalorimetric (isothermal titration calorimetry) techniques. In the absence of a chiral environment, PRNL enantiomers are strongly physisorbed on the AuNPs modified surface, yet no significant difference was recorded in the oxidation peak potential (+0.778 V R(+)-PRNL versus +0.78 V for S(-)-PRNL). Upon decorating AuNPs with l-Cys, an ∼40 mV anodic shift is recorded for S(-)-PRNL due to a more favored orientation of its diastereoisomer on the electrode's surface towards electron transfer. Interestingly, by altering the conformation of the diastereoisomeric chiral selector (replacing l-Cys with d-Cys), the enantioselective nature of the recorded electrochemical signals fades out. Additionally, the potential synergistic effects of a dual chiral system, based on the covalently bound l-/D-Cys−AuNPs and β-cyclodextrin (β-CD), a free, host-guest type chiral selector, added to the electrolyte, has also been studied. [Display omitted]