A　sensitive　assay　was　demonstrated　for　the　colorimetric　and　luminescent　detection　of　heparin.　Positively　charged　[Ru(phen)2np]2+　(np:　naphtho[2,3-f][1,10]phenanthroline)　can　interact　with　negatively　charged　AuNPs　through　electrostatic　interaction,　leading　to　the　luminescence　quenching　of　[Ru(phen)2np]2+via　energy　transfer　as　well　as　the　aggregation　of　AuNPs　together　with　a　color　change　in　solution　from　red　to　blue.　Upon　the　addition　of　negatively　charged　heparin　to　gold　nanoparticles　functionalized　by　ruthenium(ii)　complexes,　the　emission　of　[Ru(phen)2np]2+　recovered　due　to　the　competitive　adsorption　of　[Ru(phen)2np]2+　to　heparin　and　AuNPs.　A　linear　calibration　curve　was　obtained　in　the　0.4　μM　to　100　μM　range　and　0.1　μM　to　6　μM　with　a　low　detection　limit　of　0.22　μM　and　0.024　μM　based　on　3σ/s　for　heparin　quantification　in　buffer　solution　and　in　1%　fetal　bovine　serum　(FBS),　respectively.　Interestingly,　the　naked　eye　alone　can　judge　the　presence　of　0.02　μM　heparin　without　the　aid　of　any　advanced　instruments　by　color　change.　Thus　a　convenient　and　visual　method　to　detect　heparin　was　established.　©　2017　The　Royal　Society　of　Chemistry.