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.　(C)　2016　Elsevier　B.V.　All　rights　reserved.