Hybrid X-Ray/Optical imaging of organic fluorophores

Traditional in vivo fluorescent imaging commonly employs fluorescent protein reporters, including site-directed and enzyme-activatable conjugates. Red-shifted and NIR (700 – 900 nm) fluorophore reporters are now considered mainstream for in vivo imaging applications, due to the relatively low levels of light scatter and autofluorescence when used in living specimens. Recently, there have been reports of in vivo imaging with luminescent or fluorescent probes that are X-Ray activated (Carpenter et al., 2010; Osakada et al., 2013; 2014). This hybrid X-Ray/optical approach has the potential to offer the combined deeper imaging associated with X-Ray and functional detection associated with targeted optical agents. Reports that detail hybrid X-Ray/optical imaging with organic fluorophores are exceedingly rare. Here, we provide a preliminary, in vitro evaluation of selected, commercial organic fluorophores including anthracene, carbocyanine (Cy7), Rhodamine B (Rho), Carboxyfluorescein CF), and Squaraine Rotatxane (SR) as agents for X-Ray induced fluorescence (XRIF) imaging, using the Bruker In-Vivo Xtreme imaging system.

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