A Thrombin-Responsive Nanoprobe for <i>In Vivo</i> Visualization of Thrombus Formation through Three-Dimensional Optical/Computed Tomography Hybrid Imaging

Abstract

Early spontaneous detection of thrombin activation benefits precise theranostics for thrombotic vascular disease. Herein, a thrombin-responsive nanoprobe conjugated by a FITC dye, PEGylated Fe₃O₄ nanoparticles, and a thrombin-sensitive peptide (LASG) was constructed to visualize thrombin activation and subsequent thrombosis <i>in vivo</i>. The FITC dye was linked to the LASG coated on the Fe₃O₄ nanoparticles for sensing the thrombin activity via the Förster resonance energy transfer effect. <i>In vitro</i> fluorescence imaging showed that the fluorescence signal intensity increased significantly after incubation with thrombin in contrast to that of the control group (<i>p</i> < 0.05), and the signal intensity was enhanced with the increase in thrombin concentration. Further <i>in vivo</i> fluorescence imaging also revealed that the signal elevated markedly in the left common carotid artery (LCCA) lesion of the mice thrombosis model after nanoprobe injection, in contrast to that of the control + nanoprobe group (<i>p</i> < 0.05). Moreover, the thrombin inhibitor bivalirudin could decrease the filling defect of the LCCA. Three-dimensional fusion images of micro-CT and fluorescence confirmed that filling defects in the LCCA were nicely colocalized with fluorescence signal caused by nanoprobes. The nanoplatform based on a thrombin-activatable visualization system could provide smart responsive and dynamic imaging of thrombosis <i>in vivo</i>.