The oxidation–reduction reaction provides the possibility ofreducing metal NPs on the surface of graphene, while the reductionprocess makes it easy to oxidize graphene into grapheneoxide.74,80–84 In this fabricated system, metal NPs obviouslyturn into hot spots, with which the decorated graphene substrates can be used as SERS-active substrates. To illustrate thisphenomenon, three examples are given about metal NPs ofdifferent materials decorated on graphene/graphene oxidesheets.