Facile synthesis of fluorescent graphene quantum dots from coffee grounds for bioimaging and sensing

• The highly fluorescent PEI-GQDs are synthesized from coffee grounds.
• The PEI-GQDs exhibit enhanced band-edge photoluminescence property.
• The PEI-GQDs serve as low-cytotoxicity biological imaging agents.
• The PEI-GQDs show high selectivity for detecting Fe3+ and Cu2+.

We have developed a novel eco-friendly approach involving hydrazine hydrate-assisted hydrothermal cutting followed by functionalization with poly (ethylene imine) (PEI) for fabricating highly fluorescent graphene quantum dots from coffee grounds. The PEI-functionalized graphene quantum dots exhibit enhanced band-edge photoluminescence with single exponential decay. Their preliminary applications in bioimaging and sensing of heavy metals have been demonstrated.