Green-fluorescent nitrogen-doped carbon nanodots for biological imaging and paper-based sensing

Abstract

Green-fluorescent nitrogen-doped carbon nanodots (N-CDs) have been fabricated by hydrothermal treatment of oolong tea. The as-prepared N-CDs exhibit bright green fluorescence, excellent biocompatibility, low toxicity, and considerable optical stability. By virtue of these outstanding properties, the N-CDs have been utilized for intracellular Cu²⁺ imaging and paper-based Cu²⁺ sensing. Confocal fluorescence imaging of HepG2 cells indicates that the obtained N-CDs could visualize Cu²⁺ fluctuations in living cells without autofluorescence interference based on their highly selective and sensitive detection of Cu²⁺ ions in aqueous solution with a linear range of 0.01–75 μM and a detection limit of 2 nM. In addition, N-CD stained paper-based sensor strips have been prepared for user-friendly and convenient Cu²⁺ determination.