Tri-doped alkaline earth sulfide nanoparticles as a new class of highly efficient probe with near-IR stimulated fluorescence for in vivo and ultrasensitive bacteria targeted imaging

Abstract

Near-infrared light (NIR) stimulated anti-Stokes fluorescence imaging has unique advantages compared with conventional down-conversion fluorescence imaging, especially applied in bioimaging. However, the existing NIR induced fluorescence nanomaterials like up-conversion nanoparticles are restricted by issues like insufficient fluorescent brightness. Hence we introduce triple-doped red emission (CaS:Eu,Sm,Mn), and blue emission (SrS:Ce,Sm,Mn) alkaline earth sulfide nanoparticles (AES NPs) with ultra-bright NIR stimulated fluorescence, high brightness and variable emission wavelength make them very promising as a novel type of biolabeling probe. In this work, CaS:Eu,Sm,Mn nanoparticles and SrS:Ce,Sm,Mn nanoparticles are covalently linked with bacteria targeting moiety (teicoplanin or polymyxin B) for in-vivo and in-situ imaging of Gram-positive/negative bacteria, the in-vivo experiment demonstrates the functionalized AES NPs are able to adequately distinguish and differentiate bacterial infection between aseptic inflammation. Significantly, non-overlapping emission bands of this two AES NPs make Gram-positive/negative strain selective fluorescence imaging possible, and intense fluorescence under 980 nm light irradiation enables both high sensitivity and deep tissue imaging. Further, low biological toxicity of the bacteria targeting probe based the AES NPs is assessed. We conclude that CaS/SrS based system has a high potential and practical value for in vivo bacteria fluorescent imaging and detection.