Er 3+ ‐Doped Y 2 O 3 Nanophosphors for Near‐Infrared Fluorescence Bioimaging Applications

Rare‐earth‐doped ceramic nanophosphor ( RED ‐ CNP ) materials are promising near‐infrared ( NIR ) fluorescence bioimaging ( FBI ) agents that can overcome problems of currently used organic dyes including photobleaching, phototoxicity, and light scattering. Here, we report a NIR – NIR bioimaging system by using NIR emission at 1550 nm under 980 nm excitation which can allow a deeper penetration depth into biological tissues than ultraviolet or visible light excitation. In this study, erbium‐doped yttrium oxide nanoparticles ( Er 3+ : Y 2 O 3 ) with an average particle size of 100 and 500 nm were synthesized by surfactant‐assisted homogeneous precipitation method. NIR emission properties of Er 3+ : Y 2 O 3 were investigated under 980 nm excitation. The surface of Er 3+ : Y 2 O 3 was electrostatically PEG ylated using poly (ethylene glycol)‐ b ‐poly(acrylic acid) ( PEG ‐ b ‐ PAAc ) block copolymer to improve the chemical durability and dispersion stability of Er 3+ : Y 2 O 3 under physiological conditions. In vitro cytotoxic effects of bare and PEG ‐ b ‐ PAAc ‐modified Er 3+ : Y 2 O 3 were investigated by incubation with mouse macrophage cells (J774). Microscopic and macroscopic FBI were demonstrated in vivo by injection of bare or PEG ‐ b ‐ PAAc ‐modified Er 3+ : Y 2 O 3 into C57BL/6 mice. The NIR fluorescence images showed that PEG ‐ b ‐ PAAc modification significantly reduced the agglomeration of Er 3+ : Y 2 O 3 in mice and enhanced the distribution of Er 3+ :Y 2 O 3 .