In Vivo Imaging of Hypoxia Associated with Inflammatory Bowel Disease by Cytoplasmic Protein-Powered Fluorescence Cascade Amplifier.

Accurate and sensitive imaging of hypoxia associated with inflammatory bowel disease (IBD) is significant for precise diagnosis and treatment of this disease, but it remains a challenge for traditional hypoxia-activatable fluorescence probes because of more moderate hypoxic state during IBD than under other pathological conditions. To address this issue, herein, we design a hypoxia-activatable and cytoplasmic protein-powered fluorescence cascade amplifier, named HCFA to image of hypoxia associated with IBD in vivo. In our design, 4-aminobenzoic acid (azo)-modified mesoporous silica nanoparticle (MSN) was used as container to load black hole quencher 2 (BHQ2) and cytoplasmic protein-binding squarylium dye (SQ), then the -cyclodextrin polymer (-CDP) combined with azo through host-guest interaction to form HCFA. Upon passive stagnate in inflamed tissue of IBD, the azo band would be cleaved under hypoxic microenvironment and SQ was released to activate the fluorescence of HCFA. Moreover, the unconstrained SQ can bind with cytoplasmic protein to exhibit drastic fluorescence intensity enhancement, realizing the fluorescence signal amplification for imaging of hypoxia. Take the advantage of large load capacity of MSN and unique property of SQ, HCFA can sense oxygen levels in the range of 0% to 10%. Meanwhile, the fluorescence imaging results demonstrate that HCFA can sensitively distinguish different levels of cellular hypoxia and monitor the variations of hypoxia in vivo, highlighting HCFA as a promising tool for detection of hypoxia associated with IBD.