Morus nigra-derived hydrophilic carbon dots for the highly selective and sensitive detection of ferric ion in aqueous media and human colon cancer cell imaging

Strongly fluorescent hydrophilic carbon dots (CDs) were synthesized through a one-step hydrothermal route using polysaccharide-rich Morus nigra fruit as the carbon source. These Morus nigra CDs (M-CDs) were extensively characterized using various analytical techniques to determine their structural and optical properties. The as-synthesized M-CDs were determined to be monodispersed with a mean diameter of 4.5 nm. Aqueous M-CD dispersions are brownish-yellow in color in daylight and emit bright cyan-blue light upon exposure to ultraviolet light. The M-CDs exhibit typical excitation-dependent emission behavior, with a high quantum yield of 24%. The analytical data show that the as-synthesized M-CDs exhibit strong fluorescence (FLR) and are very optically stable. Hence, the as-synthesized M-CDs are expected to use as fluorescent sensors for the highly selective and sensitive detection of Fe³⁺ ions by the fluorescence quenching mechanism. The quenching rate was linearly dependent on Fe³⁺ concentration, with a Fe³⁺ detection limit of 0.47 μM and a 5–30 µm detection range. Moreover, human colon cancer (HTC-116) cells were stained with the prepared M-CDs for 12 and 24 h for cell viability and microscopic analyses. The M-CDs-conjugated HTC-116 cells were brightly multicolor illuminated, emitting blue, green, and red light when excited through 405-, 488-, and 555-nm filters with distinct excitation ranges, respectively. This study provides a new route for the large-scale synthesis of highly fluorescent CDs for diverse applications using green sources and one-step hydrothermal carbonization procedures.