Chiral discrimination of l-DOPA via l/d-tryptophan decorated carbon quantum dots

Chiral detection plays a crucial role in drug development by ensuring the purity and efficacy of drugs. This enables researchers to accurately identify and quantify chiral molecules, thereby determining the active form of a drug and avoiding the potential side effects associated with the inactive form. Chiral carbon quantum dots (CQDs) have garnered attention in the field of biomaterials science due to their distinctive chiroptical and electronic properties, as well as their biocompatibility, ease of synthesis, excellent photostability, and convenient surface functionalization. In this study, we successfully synthesized chiral probes using a one-pot chemical synthesis process. Specifically, we synthesized chiral CQDs via one-step hydrothermal synthesis of l/d-tryptophan and citric acid. Comprehensive characterization techniques, including FT-IR, PL, UV-vis, XRD, circular dichroism, H-1 and C-13 NMR, FESEM, AFM, TEM, and HRTEM, were employed to characterize the chiral CQDs. Notably, to the best of our knowledge, this study represents the first instance of well-defined chiral CQDs acting as probes for the chiral detection of l-DOPA. We evaluated the PL responses of the chiral CQDs to various chiral analytes such as cysteine, tryptophan, lysine, arginine, proline, histidine, d-penicillamine, l-DOPA, and captopril. The results demonstrate a strong interaction between the chiral l/d-Trp-CQDs and l-DOPA. Interestingly, the fluorescence spectrum of the l-Trp-CQDs remained unchanged upon the addition of l-DOPA. In contrast, d-Trp-CQDs exhibited a distinct response. When l-DOPA was introduced into the d-Trp-CQD solution, a new shoulder gradually emerged at 418 nm. This indicates that the d-Trp-CQDs exhibited a linear response (R-2 = 0.99) within the concentration range of 37-4000 nM of l-DOPA. Also, the limit of quantification (LOQ) and limit of detection (LOD) were calculated to be 37 and 11.2 nM, respectively. Therefore, chiral CQDs hold significant promise for enantioselective detection in the pharmaceutical industry and in other related fields. It offers a valuable means to ensure the safety and efficacy of pharmaceutical products.