Fig. 1

Characterization and in vivo NIR-II imaging of FE-2PEG. a Molecular structure of FE-2PEG. b Absorption and emission spectra of FE-2PEG. c The NIR-II fluorescence images of FE-2PEG and ICG under continuous irradiation of 808 nm laser at different time points. 65 mW/cm²; Over 1100 nm collection. d The normalized fluorescent intensity analysis of (c). e The NIR-II fluorescence images of the mice’s blood post-injection of FE-2PEG and ICG at different time points. (f) The qualitative and normalized fluorescent intensity analysis of (e) (n = 3, data are shown as mean ± SD). g Representative NIR-II imaging of mesenteric LNs post-injection of FE-2PEG at the cecum; The outline profiles of the lymphoid follicles (A) were delineated, and the lymphoid sinus (B), the afferent (C) and efferent lymphatic vessels (D) were illuminated. Scale bar: 1 mm. In the photograph of exposed mice, the white arrow shows the local injection site, and the red dotted line shows the mesenteric lymph node. h The normalized fluorescent intensity curve of mesenteric LNs (n = 5, data are shown as mean ± SD)