An RNA aptamer selected for binding to the fluorogenic cyanine dye, Dimethylindole Red (DIR) also binds and activates another cyanine, Oxazole Thiazole Blue (OTB), giving two well resolved emission colors. The aptamer binds each dye with sub-micromolar K<sub>D</sub> values and the resulting fluoromodules exhibit fluorescence quantum yields ranging from 0.17-0.51 and excellent photostability. The aptamer was fused to a second aptamer previously selected for binding to the epidermal growth factor receptor (EGFR) to create a bifunctional aptamer that labels cell-surface EGFR on mammalian cells. The fluorescent color of the aptamer-labeled EGFR can be switched between blue and red <i>in situ </i>simply by exchanging the dye in the medium. The promiscuity of the aptamer can also be used to distinguish between cell-surface and internalized EGFR based on addition of red or blue fluorogen at different times.

Fluoromodules consisting of a promiscuous RNA aptamer and red or blue fluorogenic cyanine dyes: Selection, characterization and bioimaging

256th National Meeting (2018)

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