Aldehyde-Functionalized Eu(III) Helicate for l-Cysteine-Specific CPL Detection through Cyclization-Induced M-Helix...

l-Cysteine (Cys) levels are linked to many health issues and serve as critical diagnostic criteria for various diseases. However, their highly specific recognition and determination from complex biological matrices remain challenging due to interference from biothiol-containing analogs, such as homocysteine (Hcy) and glutathione (GSH). Herein, by strategically positioning eight aldehyde groups at the periphery of a dinuclear Eu(III) helicate, we achieved the specific determination of l-Cys via an induced negative circularly polarized luminescence (CPL) signal (gmax ≈ -1.22, 595 nm). 1H NMR and ESI-MS combined with single-crystal X-ray crystallography and DFT calculations revealed that the size match between the periphery pocket in the helicate and the thiazolidine ring formed by l-Cys and aldehyde cyclization contributed to this CPL response, which creates a large energy difference (∼37.6 kcal/mol) between diastereoisomers and a M-helical preference. While the L-Hcy only resulted in a weak and positive signal (glum ≈ 0.15) due to the larger ring size, the GSH was CPL silent due to the non-cyclization reaction. Benefiting from the large glum value, the probe exhibited the high sensitivity for l-Cys in water or bovine serum albumin (BSA), with a detection limit lower than 8.11 × 10-7 M. Additionally, to facilitate commercial applications, a "test strip-like" hydrogel hybrid film was prepared, which still retains sensing capability to l-Cys. This work therefore provides a strategy for l-Cysteine detection by virtue of induced helical chirality of metallosupramolecules and strong lanthanide CPL.