The　abnormal　expression　of　miRNA-21　is　closely　related　to　many　cancers,　and　its　sensitive　detection　plays　an　important　role　in　the　diagnosis　and　treatment　of　cancers.　In　the　report,　we　designed　a　non-enzymatic　amplification　sensing　system　based　on　the　catalytic　hairpin　assembly　(CHA)　and　palindrome-based　hybridization　chain　reaction　(PHCR)　technique　for　the　detection　and　imaging　of　miRNA　in　living　cells.　Based　on　PHCR　technology,　two　ingeniously　designed　palindrome-contained　fluorescently　labeled　hairpin　probes　are　sequentially　opened　upon　the　stimulation　of　short　oligonucleotide　triggers,　promoting　the　autonomous　assembly　of　cross-linked　network-like　structures　(CNSs)　and　generating　fluorescence　resonance　energy　transfer　(FRET)　signal.　Moreover,　the　PHCR　technique　can　be　combined　with　CHA　technology　to　sufficiently　improve　amplification　efficiency　and　signal　output.　By　utilizing　the　CHA-PHCR　sensing　system,　one　miRNA-21　activates　many　triggers　through　CHA　process　and　in　turn　initiates　the　assembly　of　CNSs　by　PHCR　reaction,　efficiently　amplifying　the　FRET　signal　output.　As　such,　the　sensing　system　can　detect　target　miRNAs　down　to　10 pm　with　high　detection　specificity.　Moreover,　the　CNS　exhibits　the　enhanced　intracellular　stability,　enabling　the　living　cell　imaging　of　miRNA-21.　The　CHA-PHCR　sensing　system　can　also　screen　the　expression　level　of　miRNA-21　in　different　living　cells　and　differentiate　cancer　cells　from　healthy　cells,　which　is　consistent　with　the　gold-standard　PCR　method.　©　2025.　The　Author(s),　under　exclusive　license　to　Springer　Science+Business　Media,　LLC,　part　of　Springer　Nature.