Carbon Nanodots with Dual Capabilities: Glutamic Acid Sensor and Plant Growth Promoter under LED Stress Conditions

Long investigated for its physiological functions, glutamic acid (Glu) is a crucial amino acid implicated in plant development and stress responses. However, there is still limited in vivo monitoring of Glu. Here, we report the design of a "turn-on" fluorescence nanosensor for the selective detection of Glu: a nitrogen-doped carbon quantum dot (N-CQD)/Cu²⁺ complex. Cu²⁺ ions quenched the fluorescence of N-CQDs, which was then selectively recovered when Glu was added. This allowed for sensitive detection via a fluorescence recovery mechanism. The sensing technology showed outstanding selectivity, biocompatibility, and quick response. Dynamic quenching was verified as the underlying mechanism by characterization using FT-IR, XPS, DLS, and TCSPC. The uptake of N-CQDs and N-CQDs/Cu²⁺ complexes in Vigna radiata stem tissues was visualized by confocal laser scanning microscopy (CLSM), with preferential accumulation in the interfascicular, vascular bundle, and epidermal areas. Notably, Glu pretreatment affected the internalization of nanoparticles by modulating fluorescence intensity in a concentration-dependent manner. Remarkably, N-CQDs alone enhanced plant growth under LED light stress, indicating that they may function as regulators of plant development. These results offer a platform that can be used for the biological manipulation of glutamic acid in plants as well as real-time monitoring.