Fluorescent DNA nanotags based on a self-assembled DNA tetrahedron.

Progress in fluorescence detection and imaging technologies depends on the availability of fluorescent labels with strong light absorption/emission characteristics. We have synthesized intercalator dye arrays on a compact 3-dimensional DNA-tetrahedron nanostructure. The template tolerates the structural distortions introduced by intercalation and allows concentration of multiple fluorophores within a small volume, resulting in brightly fluorescent nanotags with effective extinction coefficients in the order of 10(6) M(-1) cm(-1). Efficient energy transfer from intercalated donor dyes to covalently attached acceptor dyes in the nanotags allows the emission wavelength to be shifted to the red relative to the excitation light, providing wavelength tunability. The compact nature of the supramolecular DNA tetrahedron also provides a protective medium for the fluorophores, leading to improved photostability and enhanced resistance to nuclease digestion, relative to one- or two-dimensional nanotags described previously.

A rainbow of fluoromodules: a promiscuous scFv protein binds to and activates a diverse set of fluorogenic cyanine dyes.

Combined magnetic and fluorescence cell sorting were used to select Fluorogen Activating Proteins (FAPs) from a yeast surface-displayed library for binding to the fluorogenic cyanine dye Dimethyl Indole Red (DIR). Several FAPs were selected that bind to the dye with low nanomolar Kd values and enhance fluorescence more than 100-fold. One of these FAPs also exhibits considerable promiscuity, binding with high affinity to several other fluorogenic cyanine dyes with emission wavelengths covering most of the visible and near-IR regions of the spectrum. This significantly expands the number and wavelength range of scFv-based fluoromodules.