Simple and user-friendly nucleolus imaging with ultra-narrow bandwidth red emission carbon dots

Abstract

The nucleolus has emerged as a promising target for cancer diagnosis and therapy, with its imaging being crucial for both fundamental research and clinical applications. Fluorescence imaging is a powerful tool for this purpose. However, its use is limited by the scarcity of fluorescent agents that specifically target the nucleolus and have excellent biocompatibility. Carbon dots (CDs) are becoming a valuable tool for cellular imaging because of their excellent optical properties and low toxicity. In this work, for the first time, ultra-narrow bandwidth emission CDs were synthesized with nicotinamide (NAM) and o-phenylenediamine (o-PDA) for nucleolus imaging. The reaction was carried out at 180 °C for 8 h in a stainless-steel autoclave, using a facile, low-cost, and one-step solvothermal approach with H₂O/H₂SO₄ as solvent. Prepared CDs emit red emission at 617 nm with an ultra-narrow full width at half maximum (FWHM) of 28.1 nm and quantum yield (QY) of 13 %. Moreover, the cytotoxicity assay demonstrated that CDs exhibited excellent biocompatibility with MCF-7 breast cancer cells, even at concentrations as high as 4.5 mg/mL. Finally, fixed and live cell imaging results indicate that prepared CDs show bright red fluorescence in the nucleoli of MCF-7 cells. Our results demonstrate the efficacy of prepared CDs in nucleolus imaging, offering a convenient and promising fluorescent probe that can be used for fixed and live cell nucleolus imaging.