A Dual-Mode Near-Infrared Optical and Photoacoustic Imaging Agent Based on a Low Energy Absorbing Ytterbium Complex.

Near-infrared (NIR) luminescence and photoacoustic (PA) imaging have attracted increasing attention for the real-time monitoring of biological samples due to high sensitivity, resolution, and pronounced signal detection depth, respectively. For improved contrast, both techniques require imaging agents possessing high absorption in the red-NIR range. Herein, we took advantage of a ternary complex formed with the anionic ytterbium(III) tetrakis (2-thenoyltrifluoroacetonate) ([Yb(tta) 4 ] - ) and the cationic NIR-absorbing chromophore, 1,1'-diethyl-2,2'-dicarbocyanine (Cy + ), to evaluate its potential to act as a dual-mode NIR luminescence and PA imaging agent. We demonstrated that, upon excitation with red-NIR light, Cy[Yb(tta) 4 ] encapsulated into polystyrene nanoparticles is able to generate both NIR Yb 3+ emission and a PA signal in an imaging experiment performed in a tissue-mimicking phantom.