Employing metformin-directed carbon dots with room-temperature phosphorescent towards the dual-channel detection of L-tryptophan

Currently, carbon dots (CDs) with the eminent phosphorescence have been extensively concerned owing to their more widespread applications. Herein, we employed metformin as the carbon source and successfully synthesized one kind of room-temperature phosphorescence (RTP) CDs doped with the elements of N, P through a facile microwave method. Significantly, the RTP emission of CDs appeared while the solution was fixed on the filter paper. To be specific, the hydrogen bonds formed between CDs and the filter paper, which led to the restriction of molecular rotations and motions. Again, the non-radiation attenuation rate of the excited triplet state was reduced by rigidifying the whole system, thus inhibiting the non-radiative transitions and boosting their RTP emission CDs. Interestingly, the proposed CDs could serve as the RTP ink and was applied to paint various patterns and prepare CDs-PVA film with both fluorescence and phosphorescence. Moreover, both their fluorescence and phosphorescence of these CDs was obviously enhanced by introducing L-tryptophan, thus establishing an innovative dual-channel detection of L-trp. Besides, the detection mechanism was also explored, and the increased hydroxyl-groups enhanced their fluorescence of CDs through the radiative recombination by L-trp, while the phosphorescence was enhanced by the narrowed the energy gap (∆EST), thus promoting the singlet-to-triplet intersystem crossing (ISC).