Facile synthesis of broadband red-emitting hydrophilic carbon dots for zebrafish imaging application

Red luminescence is crucial in bio-applications because of its high penetration and low photo-damage to tissue. Hydrophobicity is a major drawback to most of the reported red-emitting carbon dots (CDs), which limits their application due to poor dispersion and low quantum efficiency in aqueous phase. To solve this problem, we prepared carbon dots with broadband red emission using a simple hydrothermal process, using Congo red and m-phenylenediamine as raw materials. CDs demonstrated a bright and excitation-independent emission at ∼600 nm with FWHM of 125 nm. The CDs aqueous solution shows bright red luminescence with PLQY of 6.13 %. Meanwhile, the CDs exhibit good properties like salt tolerance, anti-photobleaching, and low cytotoxicity. As a proof-of-concept experiment, CDs were utilized to cultivate zebrafish embryos and larvae, displaying clear fluorescence images of uptake and metabolism, which further demonstrates its potential in biological imaging applications.