Utilizing　the　nucleic　acid-based　self-assembly　technology,　Y-shaped　backbone-rigidified　DNA　triangles　with　substantially　enhanced　nuclease　resistance　are　built　by　designing　a　Y-shaped　backbone　in　the　center　of　a　planar　DNA　triangle.　Along　this　line,　we　developed　aptamer-targeted　DNA　triangle-based　molecular　beacon　(Apt-Tri-MB)　probes　for　monitoring　the　microRNA　expression　in　living　cells　with　high　sensitivity　and　specificity.　For　the　Apt-Tri-MB　probe,　the　MB　is　protected　by　the　DNA　triangle　from　unwanted　enzymatic　digestion,　and　a　targeting　ligand　aptamer　is　introduced　to　endow　the　MB　with　active　tumor　cell-targeting　capability.　Thus,　the　digestion-induced　false-positive　signal　is　avoided,　and　the　background　fluorescence,　which　originates　from　the　passive　cell　uptake　(e.g.,　transfection)　of　reporting　probes,　is　substantially　suppressed.　The　imaging　capability　of　the　Apt-Tri-MB　is　superior　to　the　commercial　transfection　agent-based　counterpart　and　exhibits　good　universality　suitable　for　imaging　different　miRNAs　by　changing　the　recognition　fragment　of　the　MB.　Meanwhile,　the　disadvantages　are　efficiently　circumvented,　including　the　susceptibility　of　nucleic　acids　to　nuclease-mediated　degradation,　inability　of　MB　probes　to　enter　cells,　lipofectamine-determined　cellular　cytotoxicity,　and　nontargeting　cell　uptake.　Inspired　by　the　Y-shaped　backbone-rigidified　Apt-Tri-MB,　we　also　constructed　X-shaped　backbone-rigidified　quadrangle-based　probes　(Apt-Qua-MB).　The　experimental　results　show　that　cell　imaging　and　antidegradation　capability　of　Apt-Qua-MB　are　comparable　with　Apt-Tri-MB.　As　a　proof-of-concept　study,　the　Apt-Tri-MB　is　expected　to　open　an　exciting　avenue　for　the　further　application　of　nucleic　acid　probes　in　the　cellular　level　research　and　clinical　disease　diagnosis.　Copyright　©　2020　American　Chemical　Society.