Sensitive　detection　of　cancer　biomarker　microRNAs　(miRNAs)　is　of　vital　importance　for　cancer　diagnosis　and　treatment.　Nonetheless,　the　detection　sensitivity　in　the　existing　miRNA　bioassays　is　severely　limited　by　the　structural　characteristics　of　miRNA　(including　small　length　and　high　sequence　homology)　because　most　of　these　methods　are　based　on　target　amplification.　Herein,　we　report　a　novel　approach　to　sensitive　and　specific　detection　of　low-abundance　miRNA　via　a　unique　strategy　of　nanoprobe　dissolution-enhanced　fluorescence　amplification,　in　which　a　capture　probe　featuring　molecular　beacon　structure　is　designed.　By　means　of　this　strategy,　miRNA-21　was　detected　in　a　linear　range　from　10　fM　to　100　pM　with　a　detection　limit　as　low　as　1.38　fM.　High　selectivity　of　the　newly　developed　biosensor　was　demonstrated　by　the　good　discrimination　against　a　target　with　a　single-base　mismatch.　Furthermore,　this　assay　was　used　for　the　detection　of　miRNA-21　added　into　fetal　bovine　serum　samples　with　the　recovery　in　the　range　of　90.2%-108%　and　coefficients　of　variation　below　10.1%,　indicating　its　promising　applications　to　RNA　immunoassays　and　early　cancer　diagnosis.