In Vivo Monitoring of GABA by N-Doped Carbon Quantum Dots

Abstract

γ-Aminobutyric acid (GABA) is one of the primary inhibitory neurotransmitters and encompasses 10−30% of the neurons in the CNS. Fundamentally, GABA is responsible for decreasing the nervous system activity by inhibiting the action potential and hence excitotoxicity of neurons. Owing to these neuroregulatory features, GABA has been known to be involved in numerous diseases such as schizophrenia, epilepsy, and other psychiatric conditions. Therefore, from a neuroanatomical as well as a pathological perspective, the visual localization and relative abundance research of neurotransmitters is of great importance. The intricacies of GABA release from neurons are still largely unknown; hence, it will be necessary to analyze endogenous GABA concentrations. Here, we synthesized nitrogen-doped carbon quantum dots (N-CQDs), which employ a turn-off mechanism to detect GABA in vivo. High-resolution transmission electron microscopy (HRTEM), dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and energy-dispersive X-ray spectroscopy (EDX) have been used to verify the structural characteristics and size of the N-CQDs. Using the Stern−Volmer equation, UV−vis and fluorescence spectroscopies, and time-correlated single-photon counting (TCSPC), the mechanism of fluorescence quenching was thoroughly explained. Moreover, 0.16 μM was determined to be the N-CQD detection limit. Furthermore, exogenous GABA in human cell lines and endogenous GABA in the zebrafish forebrain (telencephalon) and midbrain (optic tectum) were both successfully detected by our sensor. Thus, this probe may be used as a competent nanosensor to detect comparative GABA levels among healthy and diseased animal models with GABA neurotransmitter imbalance and neurodegeneration.