Positively Charged and pH-sensitive Carbon Dots for Fluorescence Detection of Copper Ion

As an essential trace element in the human body, copper ion (Cu2+) performs an important role in many fundamental physiological processes that need a facile and effective method for the monitoring of Cu2+ in organisms. Herein, a turn-off, facile fluorescent strategy for sensing Cu2+ was proposed using positively charged carbon dots (P-CDs) as probe. The P-CDs prepared from melting strategy exhibited stable, biocompatible, and pH-sensitive luminescent properties. P-CDs can be selectively quenched by Cu2+ for the direct detection of Cu2+. The reaction mechanism between Cu2+ and P-CDs was systematically investigated, illustrating that Cu2+ coordinated with the surface functional groups in P-CDs. The binding effect of Cu2+ and P-CDs caused the constant morphology and static quenching behavior of P-CDs. The promising accuracy of the testing results of the addition of Cu2+ in diluted serum using P-CDs implied their extended application in the biological field.