Fluorescence imaging of FEN1 activity in living cells based on controlled-release of fluorescence probe from mesoporous silica nanoparticles

Flap endonuclease 1 (FEN1) is a structure-specific nuclease, which catalyzes the removal of 5' overhanging DNA flap from a specific DNA structure. FEN1 has been considered as an important biomarker for cancer diagnosis since it is over-expressed in various types of human tumor cells and closely related to cancer development. Nanoprobes gradually become basic tools for analyzing biomarkers variations in vivo. Here, we utilized aminoated mesoporous silica nanoparticles (NH2-MSNs) with a rich porous structure as the fluorescence nanoprobes to entrap the rhodamine 6G (Rh6G) molecules. Then gold nanoparticles linked specific single-stranded DNA (AuNPs-ssDNA) as a molecular gate was used to coat the NH2-MSNs surface. The fluorescence signal was weak when the fluorescence molecules were blocked by the AuNPs-ssDNA. In the presence of FEN1, it recognized and cleaved the specific ssDNA to release the Rh6G from NH2-MSNs, which resulted in recovered fluorescence signals. Thus, the sensitive detection of FEN1 activity was realized by controlled-release of Rh6G. The fluorescence signal showed a good linear relationship with the logarithm of FEN1 activity ranging from 0.05 to 1.75 U with a detection limit of 0.03 U. Moreover, confocal imaging demonstrated that the proposed biosensor could distinguish tumor cells from normal cells. Therefore, this technique contributes to clinical diagnostic and therapeutic monitoring.