Highly Photoluminescent Amino-Functionalized Graphene Quantum Dots Used for Sensing Copper Ions

Herein, we report a new kind of highly fluorescent probe for Cu2+ sensing generated by hydrothermal treatment of graphene quantum dots (GQDs). After hydrothermal treatment in ammonia, the greenish-yellow fluorescent GQDs (gGQDs) with a low quantum yield (QY, 2.5%) are converted to amino-functionalized GQDs (afGQDs) with a high QY (16.4%). Due to the fact that Cu2+ ions have a higher binding affinity and faster chelating kinetics with N and O on the surface of afGQDs than other transition-metal ions, the selectivity of afGQDs for Cu2+ is much higher than that of gGQDs. Furthermore, afGQDs are biocompatible and eco-friendly, and the afGQDs with a positive charge can be easily taken up by cells, which makes it possible to sense Cu2+ in living cells. The strategy presented here is simple in design, economical, and offers a mix-and-detect protocol without dye-modified oligonucleotides or complex chemical modification.