Herein　a　versatile　colorimetric　biosensing　platform　was　designed　for　sensitive,　specific,　and　rapid　screening　of　cancer-derived　exosomes　(HepG2　cell-derived)　by　introducing　horseradish　pemxidase　-encapsulated　DNA　nanoflowers　(HRP-DF)　as　the　biorecognition　elements　and　signal-generation　tags.　HRP　was　concurrently　associated　with　the　growing　ultralong-chain　DNA　and　the　magnesium　pyrophosphate　crystals　(Mg(2)PPi)　during　the　rolling　circle　amplification　(RCA),　thereby　ultimately　leading　to　the　direct　fixation　of　HRP　in　DFs.　For　demonstration,　a　linear　DNA　circular　molecule　encoding　the　complementary　sequence　of　CD63　aptamer　(a　nucleic　acid　sequence　that　can　highly　bind　to　exosomes)　was　used　as　a　starting　amplification　template　to　obtain　HRP-DF　with　the　high　biorecognition　ability　of　exosomes.　Upon　addition　of　target　exosomes,　a　sandwiched　reaction　was　carried　out　between　the　cholesterol-modified　DNA　probes-conjugated　magnetic　bead　(MB)　and　the　HRP-DFs,　accompanying　formation　of　ternary　complexes　(MB-exosomes-HRP-DF).　After　simple　magnetic　separation,　the　HRP　carried　on　the　ternary　complexes　(MB-exosomes-HRP-DF)　initiated　oxidation　of　2,2＇-azino-bis(3-ethyl-benzothiazoline-6-sulphonic　acid)　(ABTS,　nearly　colorless)　into　green-colored　oxidized　ABTS　in　the　presence　of　hydrogen　peroxide　(H2O2).　The　obvious　color　change　(from　nearly　colorless　to　dark　green)　of　ABTS-H2O2　system　can　be　easily　observed　with　the　naked　eye　and　accurately　monitored　by　UV-visible　spectrometry,　which　was　also　proportional　to　the　concentration　of　exosomes.　Impressively,　HRP-DF-based　biosensing　platform　exhibited　satisfactory　colorimetric　responses　toward　target　exosomes　within　the　working　range　from　5.0　x　10(3)　to　5.0　x　10(6)　particles/mu　L　at　a　low　detection　limit　of　3.32　x　10(3)　particles/mu　L.　Combined　with　a　one-step　sandwich　reaction,　magnetic　separation　and　HRP-DF-based　color-changing,　this　system　had　the　advantages　of　acceptable　accuracy,　strong　anti-interference　ability　and　good　reproducibility.