Recently　we　demonstrated　oriented　formation　of　gold　nanoparticle　(AuNP)　dimers　for　ultrasensitive　sensing　oligonucleotides　(J.　Am.　Chem.　Soc.　2013,　135,　12338).　Herein,　we　investigate　the　reverse　process　of　this　sensing　mechanism　using　target　analytes　to　disassemble　the　orient-aggregated　AuNP　dimers.　This　enables　us　to　expand　the　analytes　from　oligonucleotides　to　other　molecules,　e.g.　highly　sensitive　and　selective　determination　of　microcystin-LR　(MC-LR)　is　selected　for　a　demonstration　in　this　work.　Aptamers　specific　to　the　target　molecules　are　used　as　linkers　to　prepare　the　AuNP　dimers.　In　the　presence　of　the　target　molecule,　the　aptamer　changes　its　structure　to　bind　the　target　molecule.　Thus　the　pre-formed　AuNP　dimers　are　disassembled.　As　a　result,　the　solution　color　is　changed　from　blue　to　red.　This　sensing　design　retains　the　advantages　of　the　previously　developed　sensors　based　on　target　molecules　guided　formation　of　AuNP　dimers,　e.g.　the　overwhelming　sensitivity　and　stability　comparing　with　those　non-oriented　sensors　based　on　the　formation　of　large　aggregates,　with　the　additional　advantages　as　follows:　1)　the　target　molecules　are　expanded　from　oligonucleotides　to　arbitrary　molecules　that　can　specifically　bind　to　aptamers;　2)　the　color　change　is　completed　within　5.　min,　while　the　previous　sensor　based　on　the　formation　of　AuNP　dimers　cost　~1.　hour　to　obtain　stable　responses.　©　2015　Elsevier　B.V.