Exosomes　may　be　used　as　a　crucial　medium　for　the　early　diagnosis　and　potential　therapy　of　tumors　because　of　containing　a　variety　of　biological　information.　Therefore,　the　accurate　quantitative　analysis　of　exosomes　is　especially　important　in　the　biomedical　field.　Herein,　we　proposed　a　washing-free　aptasensor　based　on　luminescence　resonance　energy　transfer　(LRET)　between　rare-earth　doped　upconversion　nanoparticles　(UCNPs)　donor　and　tetramethyl　rhodamine　(TAMRA)　acceptor　for　highly　sensitive　detection　of　exosomes.　Therein,　the　combination　of　UCNPs　and　TAMRA　can　be　achieved　through　the　coupling　of　aptamers　to　the　epithelial　cell　adhesion　molecule　(EpCAM),　the　highly　expressed　surface　proteins　of　the　exosomes.　Therefore,　when　the　system　of　UCNPs-TAMRA　in　the　presence　of　exosomes　is　excited　by　near-infrared　light　at　980　nm,　TAMRA　emits　yellow　fluorescence　at　585　nm　due　to　LRET.　As　a　result,　the　fluorescence　intensity　at　585　nm　is　linearly　correlated　to　the　concentration　of　exosomes,　which　is　available　for　the　detection　and　quantification　of　exosomes.　Under　optimal　conditions,　the　proposed　approach　can　reach　a　low　limit　of　detection　(LOD)　of　80　particles/μL,　and　effectively　reduce　the　background　signal　by　using　UCNPs　as　an　energy　donor.　Moreover,　this　proposed　aptasensor　can　be　universally　applied　to　the　detection　of　other　targets　by　strictly　screening　the　aptamers.　©　2019　Elsevier　B.V.