Introduction: The blood–brain barrier (BBB) serves as a critical defence mechanism, protecting the brain from harmful substances. This protective layer is a selective, semi-permeable membrane that restricts the passage of most compounds, allowing only a limited range of substances to traverse it. The optical properties of carbon quantum dots (CQDs) render them exceptional tools for bioimaging applications. Zebrafish, as an important animal model, share significant physiological and genetic similarities with mammals, particularly humans. In this study, CQDs are employed for the bioimaging of zebrafish brains, demonstrating their utility in neurobiological research.

Methods: CQDs were prepared from caffeic acid using the hydrothermal method for 4 hours. The morphological characterization and optical properties of the CQDs were evaluated. The synthesized CQDs were injected into zebrafish and incubated for 24 and 48 hours. Post incubation, the zebrafish were sacrificed and brain sections were observed under epifluorescence microscope.

Results and discussion: The morphological , chemical, and optical characterization of CQD confirms the synthesis of CQDs with photoluminescence properties. Zebrafish brain sections were observed under an epifluorescence microscope, allowing for the detailed visualization of the fluorescence within the neural tissue. Moreover, our findings demonstrate that CQDs successfully traversed the blood–brain barrier (BBB), evidenced by their presence within the brain of the zebrafish specimens.

Conclusion: The detailed visualization of zebrafish brain sections demonstrated the presence of CQDs within the neural tissue, validating their capability to cross the highly selective blood–brain barrier (BBB). This finding highlights the potential of CQDs for applications in neurobiological research and therapeutic strategies. The promising results of this study lay a foundation for the development of CQD-based applications in the realms of neuroscience, diagnostics, and nanomedicine.