Color-tunable graphene quantum dots via one-step nitrogen-induced intramolecular charge transfer for in vivo/vitro aminotransferase fluorescence sensing

Monitoring aspartate aminotransferase (AST) has been demonstrated to be a sensitive sign of liver dysfunction and an essential method for determining the health status of the living body. The quantitative analysis of AST in vivo/vitro is still challenged by complicated processes, expensive equipment, and/or limited sensitivity. A colorimetric assay using multicolored fluorescent nanomaterials holds great promise in vivo/vitro sensing for visual and highly sensitive disease diagnosis. However, achieving a one-step synthesis of multicolored fluorescence (FL) GQDs probe presents challenges. Herein, we successfully designed novel multicolored GQDs with a high quantum yield (QY) of 60.7 % via a simple nitrogen-induced intramolecular charge transfer (ICT) approach. Leveraging the non-toxic and color-tunable properties of N-GQDs, we developed an innovative N-GQDs-based FL test paper for sensitive colorimetric on-site detection of AST, employing the FL colorimetric method based on the transamination reaction. The FL quenching intensity demonstrated an excellent linear relationship with the concentration of AST within the range of 2.0-60.0 U/L, achieving an impressively low limit of detection (LOD) as low as 0.065 U/L. Moreover, the N-GQDs were utilized for AST in vivo detection and FL imaging in living zebrafish, further showcasing their potential in various applications such as liver disease diagnosis, assessment of myocardial damage, and monitoring of drug and toxic poisonings.