Alkyl-substituted cucurbit[6]uril–based fluorescent probes for glutamic acid and lysine sensing

In this study, two novel fluorescent probes, H 1 /G and H 2 /G, were constructed using two alkyl-substituted cucurbit[6]urils (CB[6]s), H 1 and H 2 , and a cationic dye guest, G. The G molecules were encapsulated within the cavities of CB[6] hosts, forming 1:1 host–guest complexes. While free G molecules exhibited negligible fluorescence in solution, the inclusion complexes demonstrated a strong fluorescence signal (618 nm). The detection limits for glutamic acid (Glu) recognition by the two probes were as low as 2.98 × 10 −7  M and 4.20 × 10 −7  M, respectively. Notably, although the two modified CB[6]s differed by only a single substituent, their resulting probes demonstrated different degrees of amino acid recognition ability. The H 2 /G probe was capable of recognizing both Glu and lysine (Lys), while the H 1 /G probe detected only Glu. By employing structurally modified CB[6]s as hosts and constructing CB[6]-based fluorescent probes capable of selectively recognizing non-aromatic amino acids, this study paves the way for the biological applications of CB[6]-based supramolecular host–guest systems.