L-tyrosine methyl ester-stabilized carbon dots as fluorescent probes for the assays of biothiols

Highlights: • A metal ions-free approach was constructed for the assays of thiols inspired by the unique feature of tyrosinase. • The fluorescence intensity of the modified CDs can be quenched with higher quenching efficiency than the unmodified ones. • Excitation-independent behavior of Tyr-CDs was observed, which helped to eliminate the effect of the background. • The fluorescence of the CDs could recover in a biothiols-concentration-dependent manner when biothiols were introduced. - Abstract: Over the past few decades, assays of biothiols had attracted much attention due to the essential role they played in human physiology, especially using the fluorescent analysis. In most cases, competitive mechanism was often employed, where the metal ions were often introduced as the quenchers and thiols competed with metal ions due to the high binding affinity and strong thiophilicity for 'signal-on' assays. To develop a metal ions-free approach for the assays of thiols, here, L-tyrosine methyl ester capped carbon dots (Tyr-CDs) were employed and prepared as the fluorescent probes. The as-prepared Tyr-CDs displayed narrow size distribution and distinct blue fluorescence with high quantum yield (12.9%) compared with the unmodified CDs. Moreover, Tyr-CDs exhibited higher quenching efficiency due to the efficient energy transfer between Tyr-CDs and the quinone products in the presence of tyrosinase. When the targeted biothiols was present, the catalytic reaction of the tyrosinase to the formation of quinone was inhibited and the fluorescence signal was recovered in a biothiols-concentration-dependent manner, which provided the basis for the analysis of biothiols. The practical application of the present system was demonstrated by testing the biothiols in human plasma samples and good recovery was obtained, indicating that the sensing platform we proposed hold great promise in the accurate detection of biothiols in complex biosystems.