Simultaneous discriminative sensing of biothiols in vitro and in living cells has remained challenging. Herein, we report a new sulfonamide-based self-quenched fluorescent probe 1 for this purpose with high sensitivity and good selectivity. Treatment of 1 with cysteine (Cys), homocysteine (Hcy), or glutathione (GSH) yields aminoluciferin, 2-cyano-6-aminobenzothiazole homocysteine (CBTHcy), or 2-cyano-6-aminobenzothiazole (CBT), turning "on" the fluorescence at wavelengths of 522, 517, or 490 nm, respectively. Kinetic study indicated that 1 reacts with Cys faster than with Hcy or GSH. With these unique properties of 1, we applied 1 for highly sensitive sensing of Cys, Hcy, and GSH among other 19 natural amino acids (AAs) with good selectivity. Confocal fluorescence microscopic imaging of 1-treated HepG2 cells at two channels (522 ± 8 and 490 ± 8 nm), together with quantitative analysis, indicated that the "turn-on" fluorescence was induced by intracellular Cys-dominating condensation and reduction of 1 but not by intracellular GSH-dominating reduction of 1. This suggests that 1 could be applied for discriminative sensing of intracellular Cys from the abundant GSH. Further development of 1 might bring about an efficient tool for probing cellular functions that relate to biothiols.
Herein, we report for the first time the use of bipyridine-based hydrogel for selective and visible detection and absorption of Cd(2+). At low concentrations, hydrogelator 1 was applied for selective detection of Cd(2+) in vitro and in living cells with high sensitivity. In the absence of metal ions, 1 is nonfluorescent at 470 nm. Upon addition of metal ions, 1 selectively coordinates to Cd(2+), causing an 86-fold increase of fluorescence intensity at 470 nm via the chelation enhanced fluorescence (CHEF) effect, as revealed by first-principles simulations. At 1.5 wt% and pH 5.5, 1 self-assembles into nanofibers to form hydrogel Gel I. Since Cd(2+) could actively participate in the hydrogelation and promote the self-assembly, we also successfully applied Gel I for visible detection and absorption of Cd(2+). With these excellent properties, Gel I is expected to be explored as one type of versatile biomaterial for not only environmental monitoring but also for pollution treatment in the near future.
Herein, we report the development of a new fluorescent switch for sequential and selective sensing of Cu(2+) and L-histidine (L-His) in vitro and in living cells for the first time. In the absence of metal ions, Ac-SAACQ-Gly-Gly-Gly-Lys (FITC) (1) exhibits comparable fluorescence to that of free FITC. In the presence of metal ions, 1 selectively coordinates to Cu(2+) , causing its fluorescence emission to be quenched via photoinduced electron transfer. Interestingly, the as-formed 1–Cu(2+) complex selectively responds to L-His among the 20 natural amino acids by turning its fluorescence on. This property of fluorescence switch of 1 was successfully applied for qualitatively and quantitatively sensing Cu(2+) and L-His in vitro. Using this dual functional probe, we also sequentially imaged Cu(2+) and L-His in living HepG2 cells. Our new probe 1 could be applied for not only environmental monitoring but also biomolecule detection in the near future.
Spontaneously precise organization of small structures into complex superstructures is ubiquitous and important in nature. But using small building blocks to mimic this process remains a challenge to scientists. Herein, we report the rational design of a bipyridine-derivative and applied it for the self-assembly of nanorings. The addition of Fe(2+) to the nanorings resulted in the assembly of the nanorings into supernanostructures via Fe(2+)-bipyridine coordination. HPLC, HR-ESI/MS, UV-vis, DLS, and TEM analyses clearly validated the intramolecular cyclization, self-assembly of the nanorings, and the additional self-assembly of the superstructures via Fe(2+)-bipyridine coordination. We envision our strategy to be a new approach of precisely assembling nanostructures of ring shape into more complex superstructures.
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