Organic Near-Infrared-Emitting Nanoparticles for X-Ray Bioimaging: A Nontoxic Alternative Harnessing Förster Resonance Energy Transfer-Based Sequential Energy Transfer

In the efforts to generate a less toxic X-Ray bioimaging contrast agent, a fully organic, radioluminescent nanoparticle system that emits in the near-infrared (NIR) region when excited with an X-Ray source is synthesized using a two-step process. First, red-emitting nanoparticles are fabricated by the emulsion copolymerization of styrene and propargyl acrylate with anthracene, naphthalimide, and rhodamine B methyl methacrylate derivatives. Subsequently, the nanoparticles are modified with silicon phthalocyanine and indocyanine green derivatives via a copper(I)-catalyzed azide/alkyne cycloaddition “click” reaction. By coupling an organic scintillator with four Förster resonance energy transfer-pairing dyes, X-Ray-induced, multiple, sequential energy transfer is exploited to convert ionizing radiation from an X-Ray source into NIR light, which is optimal for biomedical imaging. Proof-of-concept imaging studies show that the X-Ray-induced indocyanine green fluorescence from the particulate system can be visualized through porcine tissue. Additionally, toxicity studies in human embryonic kidney cells indicate that the particles are nontoxic and applicable in vivo.