Abstract
The donor donor-acceptor (DD-A) FRET model has proven to have a higher FRET efficiency than donor-acceptor acceptor (D-AA), donor-acceptor (D-A), and donor donor-acceptor acceptor (DD-AA) FRET models. The in-tube and in-cell experiments clearly demonstrate that the "DD-A" FRET binary probes can indeed increase the FRET efficiency and provide higher imaging contrast, which is about one order of magnitude higher than the ordinary "D-A" model. Furthermore, MnO(2) nanosheets were employed to deliver these probes into living cells for intracellular TK1 mRNA detection because they can adsorb ssDNA probes, penetrate across the cell membrane and be reduced to Mn(2+) ions by intracellular GSH. The results indicated that the MnO(2) nanosheet mediated "DD-A" FRET binary probes are capable of sensitive and selective sensing gene expression and chemical-stimuli changes in gene expression levels in cancer cells. We believe that the MnO(2) nanosheet mediated "DD-A" FRET binary probes have the potential as a simple but powerful tool for basic research and clinical diagnosis.