Cu2+ coordinated L-proline-derived carbon-nanodots for specific non-enzymatic detection of tyrosine.

Carbon-nanodots (CDs) exhibit versatile emissive and electrochemical properties, which have been widely utilized in applications such as biosensing, bioimaging, and light-emitting devices. Amino acids provide an attractive means for introducing nitrogen (N-doping) and surface functionalities with structural diversity into CDs. In this work, water-dispersible, emissive and electrochemically active L-proline derived CDs (CDs-Pro) were synthesized directly from L-proline through a mild thermal process. The supramolecular complex of the CDs-Pro with Cu2+ ions (CDs-Pro/Cu2+) was evaluated for luminescence and electrochemical non-enzymatic detection of tyrosine (Tyr). The CDs-Pro and CDs-Pro/Cu2+ nanostructures were systematically characterized using various analytical methods to confirm the emissive core structure as well as the outer-shell functionality. The optical investigations report an interesting pH-dependent photoluminescence quantum yield in the range of 1.2 to 2.2%. The surfaces of screen-printed carbon electrodes modified with the CDs-Pro/Cu2+ nanostructures showed specific non-enzymatic electrochemical recognition of Tyr over a linear range of 16-550 µM, with a limit of detection (LOD) of 61.8 µM. Meanwhile, the water dispersion of CDs-Pro/Cu2+ nanostructures exhibited specific non-enzymatic photoluminescence detection of Tyr over the range 5-350 µM, with an LOD value of approximately 0.41 µM. Moreover, assay specificity was investigated using molecular modelling methods. The formation free energy (ΔGform) values obtained for all investigated aromatic amino acids confirm a higher stability for the Pro/Cu2+/Tyr2- system (-661.86 kJ mol-1) compared to Pro/Cu2+/Trp (-640.60 kJ mol-1) and Pro/Cu2+/Phe (-637.98 kJ mol-1). Finally, this article addresses current challenges in the field of carbon-based nanostructures and outlines future research directions, emphasizing the potential of carbon-nanodots for the development of non-enzymatic assays for amino acid recognition.