DNA tetrahedral molecular sieve for size-selective fluorescence sensing of miRNA 21 in living cells.

In situ monitoring of intracellular microRNAs (miRNAs) often encounters the challenges of surrounding complexity, coexistence of precursor miRNAs (pre-miRNAs) and the degradation of biological enzyme in living cells. Here, we designed a novel probe encapsulated DNA tetrahedral molecular sieve (DTMS) to realize the size-selective detection of intracellular miRNA 21 that can avoid the interference of pre-miRNAs. In such strategy, quencher (BHQ-1) labeled probe DNA (S6-BHQ 1) was introduced into the inner cavity of fluorophore (FAM) labeled DNA tetrahedral scaffolds (DTS) to prepare DTMS, making the FAM and BHQ-1 closely proximate, and resulting the sensor in a "signal-off" state. In the presence of miRNA 21, strand displacement reaction happened to form more stable DNA double-stranded structure, accompanied by the release of S6-BHQ 1 from the inner cavity of DTMS, making the sensor in a "signal-on" state. The DTMS based sensing platform can then realized the size-selective detection of miRNA 21 with a detection limit of 3.6 pM. Relying on the mechanical rigidity of DTS and the encapsulation of DNA probe using DTMS, such proposed method achieved preferable reproducibility and storage stability. Moreover, this sensing system exhibited good performance for monitoring the change of intracellular miRNA 21 level during the treatment with miRNA-related drugs, demonstrating great potential for biological studies and accurate disease diagnosis.