Competition-Mediated FRET-Switching DNA Tetrahedron Molecular Beacon for Intracellular Molecular Detection

Recently, DNA tetrahedron-based sensors for intracellular detection have attracted more attention due to many interesting properties, including good structural rigidity, excellent biocompatibility, high resistance to enzymatic degradation, and the ability to enter cells without the use of transfection agents. However, the previous designs are still restricted by their lack of accuracy, reliability, and generality. Herein, to solve these limitations, we describe self-assembly of the competition-mediated FRET-switching DNA tetrahedron molecular beacon (CF-DTMB), and its applications for intracellular tumor-related mRNA detection. In brief, the recognition strand is partially complementary to its competitor, which is a hairpin stem-loop structure inserted in one edge of the DNA tetrahedron. In the absence of a target, a long domain of the recognition strand hybridizes with the competitor and makes the hairpin structure open, inducing the two labeled dyes to be spatially separated (FRET off). However, in the presence of the target, the competitor is substituted for the target to bind with the recognition strand, subsequently leading the formation of a stem-loop structure, which draws two dyes together (FRET on). The results demonstrate that the current strategy possesses the merits of the previous DNA tetrahedron-based sensors, but also improves the accuracy and reliability. Furthermore, we have also demonstrated that our design can become a general strategy for detecting and imaging a variety of other molecules, such as adenosine triphosphate (ATP) in living cells. Therefore, the CF-DTMB can serve as an excellent intracellular molecular detection tool, which is promising for biological and disease studies.