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

Herein, we report a new kind of highly fluorescent probe for Cu 2+ 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 Cu 2+ 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 Cu 2+ 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 Cu 2+ 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.