N-Carbon Quantum Dot/Cu Complex for In Vivo Monitoring of Glycine Levels

Neurotransmitters are chemical messengers that aid nerve cell communication; thus, the visual localization and relative abundance study of neurotransmitters hold high significance from both a neuroanatomical and pathological viewpoint. Glycine, the principal inhibitory neurotransmitter, is functionally conserved among the chordates. Found abundantly distributed in the brain stem and spinal cord, glycinergic neurotransmission helps to modulate motor pattern creation, spinal reflex synchronization, and sensory stimuli processing. Thus, the detection of endogenous glycine is vital. Here, we synthesized the N-CQDs/Cu complex to detect glycine selectively by the "turn-on" mechanism. The mechanism of fluorescence enhancement has been extensively described by using DLS, FT-IR, EDX, XPS, UV-vis, fluorescence spectroscopy, and fluorescence lifetime decay. Furthermore, the detection limit of the N-CQDs/Cu complex was found to be 10 nM. Additionally, our complex was successful in detecting exogenous glycine in human cell lines, as well as the endogenous glycine in the zebrafish brainstem and spinal cord. Thus, our carbon nanodots offer a good alternative to monitor the changes in glycine levels in response to stress, injury, or pathological conditions, such as neuromotor disorders caused by interruptions in inhibitory glycine-mediated neurotransmission.