Deciphering dual fluorescence modulation mechanisms in red carbon: selective sensing of aspartate and lysine

Amino acids are essential to all living organisms, making the monitoring of their levels in biological systems and food processing critical for diverse applications. Among analytical methods, fluorescence-based detection has emerged as a preferred approach due to its high sensitivity, rapid response, and eco-friendly profile. Herein, we report the synthesis of red carbon (RC) via a simple one-step co-heating method, which enables ultrasensitive discrimination between aspartate (Asp) and lysine (Lys). Notably, RC exhibits fluorescence enhancement with Asp and selective quenching with Lys, achieving detection limits of 16.5 and 2.0 μM, respectively. Mechanistic studies reveal distinct changes in quantum yield and fluorescence lifetime, indicating that the fluorescence modulation arises from intramolecular charge transfer (ICT). Essentially, the Lowest Unoccupied Molecular Orbital (LUMO) energy and the weak interaction between the RC and Lys can quenching the fluorescence of RC, the LUMO energy of RCAsp is lowest and the lowest gap energy of HOMO (Highest Occupied Molecular Orbital)-LUMO can further accept the electronic for enhancing the fluorescence of RC by density functional theory calculations. These findings underscore the potential of RC-based probes for precise amino acid quantitation, with further advancements in chemical sensing technologies poised to unlock broader applications in biomedical and food chemistry processing.