||Molecule-induced assembly of nanomaterials can alter their unique chemical and physical properties, which can be a promising approach for sensing. Herein, we present an optical ‘turn-on’ biosensor for the detection of matrix metallopro-teinase-2 (MMP-2), which was fabricated by means of peptide-induced assembly of fluorescent graphene oxide (GO). Functionalization of GO with a peptide substrate for MMP-2 bearing a thiol group led to its self-assembly via disulfide bonding, accompanied by self-quenching of GO’s strong fluorescence. This peptide-induced GO assembly was then disassembled by proteolytic cleavage in the presence of MMP-2, thereby restoring the level of self-quenched GO fluorescence. With this approach, we were able to detect MMP-2 and to investigate the kinetic parameters of MMP-2 activity. The GO-peptide assembly was successfully applied to the sensitive detection of MMP-2 secreted by living cells, human hepatocytes HepG2.