A\nThrombin-Responsive Nanoprobe for In Vivo Visualization\nof Thrombus Formation through Three-Dimensional Optical/Computed\nTomography Hybrid Imaging

Early spontaneous detection of thrombin\nactivation benefits precise\ntheranostics for thrombotic vascular disease. Herein, a thrombin-responsive\nnanoprobe conjugated by a FITC dye, PEGylated Fe3O4 nanoparticles, and a thrombin-sensitive peptide (LASG) was\nconstructed to visualize thrombin activation and subsequent thrombosis in vivo. The FITC dye was linked to the LASG coated on the\nFe3O4 nanoparticles for sensing the thrombin\nactivity via the Förster resonance energy transfer effect. In vitro fluorescence imaging showed that the fluorescence\nsignal intensity increased significantly after incubation with thrombin\nin contrast to that of the control group (p <\n0.05), and the signal intensity was enhanced with the increase in\nthrombin concentration. Further in vivo fluorescence\nimaging also revealed that the signal elevated markedly in the left\ncommon carotid artery (LCCA) lesion of the mice thrombosis model after\nnanoprobe injection, in contrast to that of the control + nanoprobe\ngroup (p < 0.05). Moreover, the thrombin inhibitor\nbivalirudin could decrease the filling defect of the LCCA. Three-dimensional\nfusion images of micro-CT and fluorescence confirmed that filling\ndefects in the LCCA were nicely colocalized with fluorescence signal\ncaused by nanoprobes. The nanoplatform based on a thrombin-activatable\nvisualization system could provide smart responsive and dynamic imaging\nof thrombosis in vivo.