A　colorimetric　and　luminescent　bifunctional　Ru(II)　complex-modified　gold　nano-probe　for　sensing　ctDNA　was　developed.　A　new　water-soluble　Ru(II)　complex　containing　an　aromatic　alpha-diimine　ligand　with　an　extended　pi　system　was　found　to　be　emissive　at　about　588　nm　in　water　and　the　emission　intensity　of　the　complex　was　enhanced　about　3.4-fold　upon　addition　of　calf　thymus　DNA　(ctDNA)　in　aqueous　buffer　with　no　color　changes.　The　detection　limit　was　70　nM　with　a　1.2%　relative　standard　deviation　(RSD,　n　=　5).　The　Ru(II)　complex　chromophore　was　used　to　modify　8　nm　MHA　carboxylate-functionalized　gold　nanoparticles　to　produce　a　colorimetric　and　luminescent　bifunctional　probe　for　sensing　ctDNA　in　aqueous　buffer　at　room　temperature.　The　obvious　change　in　visible　color　and　enhancement　of　emission　intensity　of　the　functionalized　gold-Ru(II)　complex　colloids　upon　addition　of　ctDNA　was　due　to　the　electron　or　energy　transfer　between　Ru(II)chromophore　and　the　Au-NPs.　The　limit　of　detection　was　1.0　nM　for　ctDNA　with　a　4.5%　RSD　(n　=　5).　With　such　a　high　sensitivity,　the　bifunctional　Ru(II)　complex-modified　gold　nano-probe　will　be　potentially　suitable　for　the　DNA　sensing　in　bioanalytical　application.　(C)　2011　Elsevier　B.V.　All　rights　reserved.