Selective turn-on fluorescent sensing of endogenous glutamate using N-CQDs/Al nanocomposites in zebrafish CNS

L-Glutamate is the primary excitatory neurotransmitter in the central nervous system, and its dysregulation is associated with numerous neurological disorders, underscoring the importance of sensitive, real-time detection in living organisms. In this study, we created a biocompatible fluorescent nanosensor using a nitrogen-doped carbon quantum dot aluminium ion composite (N-CQDs/Al) to selectively detect L-glutamate through a straightforward fluorescence "off-on" process. The N-CQDs and the complex were thoroughly analysed with DLS, TEM, FT-IR, EDX, UV-Vis, and fluorescence spectroscopy, confirming their size, surface features, and optical stability. When coordinated with Al³⁺, fluorescence was quenched, but the addition of L-glutamate revived it via competitive binding. The sensor exhibited high sensitivity, a detection limit of 0.14 µM, a wide linear range, and excellent selectivity toward common amino acids and interfering substances. Its low toxicity and robust photostability allowed for real-time in vivo monitoring of endogenous glutamate and in vitro testing in the optic tectum and retina of live zebrafish. To our knowledge, this is the first report of an N-CQDs/Al³⁺ based fluorescence "off-on" system for real-time, in vivo glutamate detection, offering a simple and efficient platform for neurotransmitter sensing and neurobiological research.