Green preparation of carbon dots for intracellular pH sensing and multicolor live cell imaging

Carbon dots are prepared using a green hydrothermal approach with dehydrated shiitake mushroom as the sole carbon source without any additives (these carbon dots are shortly termed as MCDs). Carbonization, surface functionalization and nitrogen doping are involved in the hydrothermal treatment and no further modification or surface passivation is necessary. The derived MCDs are nitrogen-doped, oxygen-rich with hydroxyl, carboxyl and amine groups, with a diameter of ca. 4.2 nm. MCDs exhibit cell permeable properties and a distinct pH-sensitive/excitation-dependent photoluminescence emission feature within pH 4.0-8.0, providing an optical probe for intracellular pH sensing and multicolor imaging of live HeLa cells. MCDs also show a strong fluorescence response to hemin, which facilitates sensitive fluorescent sensing of hemin with a detection limit of 120 nmol L^-1.