The　negatively　charged　ruthenate(II)　complex　[Ru(bpy)(PPh3)(CN)3]−　and　gold　nanoparticles　(AuNPs)　were　used　for　detecting　lysozyme　(LYS).　The　luminescence　of　the　ruthenate(II)　complex　is　quenched　by　AuNPs,　and　this　induces　the　aggregation　of　AuNPs　and　a　color　change　from　red　to　blue.　After　addition　of　lysozyme,　the　positively　charged　lysozyme　and　the　negatively　charged　ruthenate(II)　complex　bind　each　other　by　electrostatic　interaction　firstly.　This　prevents　AuNPs　from　aggregation　and　quenches　the　emission　of　the　ruthenate(II)　complex.　Its　luminescence　and　the　degree　of　aggregation　of　the　AuNPs　can　be　used　to　quantify　LYS.　The　fluorometric　calibration　plot　is　linear　in　the　0.01　to　0.20　μM　LYS　concentration　range,　and　the　calibration　plot　is　linear　between　0.02　and　0.20　μM　of　LYS.　The　color　of　the　solution　can　be　easily　distinguished　by　bare　eyes　at　0.08 μM　or　higher　concentration　of　LYS.　The　applicability　of　the　method　was　verified　by　the　correct　analysis　of　LYS　in　chicken　egg　white.　[Figure　not　available:　see　fulltext.].　©　2018,　Springer-Verlag　GmbH　Austria,　part　of　Springer　Nature.