LAUSR

N‒GQDs with an average size of ca. 20-30 nm are utilized for the picomolar detection of inhibitory neurotransmitters, glycine (Gly), in pH ca. 7.0. The crystalline nature, morphology, elemental composition, and chemical state of N-GQDs are investigated by XRD, FE-SEM, HR-TEM, XPS, and FT-IR techniques. The addition of Gly (100 × 10-9 M; 0 → 1.0 mL) steadily quenches the fluorescence intensity of N-GQD (1 × 10-6 M) at 432 nm (λex 333 nm) due to inner filter effect (IFE) through the formation of ground-state complex, N-GQD•Gly. The excitation-independent N‒GQDs showed an outstanding selectivity and sensitivity towards Gly with binding constant (Ka = 8.97 × 10-3 M-1) and LoD (21.04 pM; S/N = 3). Time-correlated single-photon counting experiment confirms the static quenching of N-GQD (8.77 → 8.85 ns) in the presence of Gly. The interference of other amino acids on the strong binding of the N-GQD•Gly complex in H2O is examined. Combinatorial Ex-OR and NOT gate logic circuits that could be useful in neuromorphic computing are developed based on the reversible fluorescence intensity changes of N-GQD upon the addition of Gly (ФF 0.54 → 0.39). The real-time application of N-GQD was investigated using commercially available relevant milk samples. Remarkably, not less than 99% cytotoxic reactivity of N-GQDs is attained against HeLa cells.