Mercury　ion　(Hg2+)　pollution　has　deleterious　effects　on　the　environment　and　human　health.　Herein,　through　one-step　biomimetic　mineralization　of　metal　salt　with　a　natural　protein,　we　develop　an　optical　sensor　system　for　Hg2+　detection　with　high　selectivity　and　sensitivity.　Glucose　oxidase　(GOD)　serves　as　both　a　template　and　reducing　agent　to　achieve　the　in　situ　biomineralization　of　Au　(III),　producing　stable　fluorescent　GOD-conjugated　gold　clusters　(GOD-AuCs)　with　a　high　yield.　The　probe　above　with　a　uniform　core　size　of　around　2.5　nm,　has　an　obvious　maximum　fluorescence　emission　peak　at　686　nm.　GOD-AuCs　exhibit　good　selectivity　to　Hg2+,　in　comparison　to　other　metal　ions　including　K+,　Na+,　Ca2+,　Mg2+,　Zn2+　and　Cu2+.　The　reason　might　be　that　the　existence　of　a　small　amount　of　Au+　(21%)　on　the　surface　of　the　cluster,　permits　strong　metallophilic　interaction　between　GOD-AuCs　and　Hg2+.　It　results　in　the　instantaneous　and　remarkable　fluorescence　quench.　Moreover,　the　intensity　of　fluorescence　quench　is　found　to　be　linearly　depended　on　the　concentration　of　Hg2+,　with　a　detection　limit　of　7.5　mu　M.　These　favorable　findings　promise　GOD-AuCs　have　a　good　potential　in　monitoring　environmental　Hg2+.　(C)　2017　Elsevier　B.V.　All　rights　reserved.