In this study, a novel fluorescent dye-doped nanobubbles were constructed, which not only can be used for contrast-enhanced ultrasound imaging, but also can effectively integrate bioluminescent energy resonance transfer (BRET) and fluorescent energy resonance transfer (FRET) to convert the blue light produced by luminol into near-infrared light. To achieve high sensitivity bioluminescence imaging of deep inflammatory tissue.

Abstract:

Inflammation is an immunological response involved in various inflammatory disorders ranging from neurodegenerative diseases to cancers. Luminol has been reported to detect myeloperoxidase (MPO) activity in inflamed area through a light- emitting reaction. However, this method is limited by low tissue penetration and poor spatial resolution. Here, we fabricated a nanobubble (NB) doped with two tandem process integrating bioluminescence resonance energy transfer (BRET) and fluorescence resonance energy transfer (FRET). This BRET-FRET process caused a 24- fold increase in detectable luminescence emission over luminol alone in an inflammation model induced by lipopolysaccharide. In addition, the echogenicity of the BRET-FRET NBs also enables perfused tissue microvasculature to be delineated by contrast- enhanced ultrasound imaging with high spatial resolution. Compared with commercially-available ultrasound contrast agent, the BRET-FRET NBs exhibited comparable contrast- enhancing capability but much smaller size and higher concentration. This bioluminescence/ultrasound dual-modal contrast agent was then successfully applied for imaging of an animal model of breast cancer. Furthermore, biosafety experiments revealed that multi-injection of luminol and NBs didn’t induce any observable abnormality. By integrating the advantages of bioluminescence imaging and ultrasound imaging, this BRET-FRET system may have the potential to address a critical need of inflammation imaging.