Fluorescence Mechanism of Red-Emitting Carbon Dots and Carbon Dot–Hydroxyapatite Nanocomposite Particles for Osteosarcoma Tracing

Accurately diagnosing bone cancer lesions and implants is a major clinical challenge. Fluorescence imaging (FI) offers precise, sensitive real-time monitoring and eco-friendly traits, making it promising for clinical use. Current fluorescent indicators using hydroxyapatite (HA) face instability and toxicity issues. We proposed a fluorescent indicator based on red-emitting, water-soluble N-, B-, and F-doped carbon dots (N,B,F-CDs) with a fluorescence quantum yield (QY) of up to 21.94%. By expanding the conjugated structure through N→B–F bonding, the emission wavelength shifted toward the red spectrum. Chemical precipitation was used to nucleate HA on N,B,F-CDs, producing red-emitting N,B,F-CDs-hydroxyapatite (CDs-HA) nanocomposite particles and increasing the QY to 23.70%. CDs-HA do not affect normal cells but could be easily endocytosed by osteosarcoma cells, enabling tracing. This study introduced possibilities for creating fluorescent N,B,F-CDs structures and applying CDs-HA for clinical detection of osteosarcoma spread or postoperative residual tumor tissue. CDs-HA are highly promising for in vivo visualization and as drug carriers.