Fig. 2. In vivo NIR-IIb imaging/tracking of subcutaneously administrated pEr-P³-RBD vaccine.

(A) Immunization schedule; female BALB/c mice (n = 10) aged 6 weeks were immunized by subcutaneous injection at the mouse tail base with the pEr-P³-RBD nanovaccine on day 0 and day 21. (B) Simplified schematic of the in vivo NIR-II imaging system. CCD, charge-coupled device. (C) NIR-IIb luminescence images (975-nm excitation with a power density of ~50 mW cm⁻², 1500- to 1700-nm detection, and the exposure time is 20 ms, continuous wave mode) showing the nanovaccine migrated from the injection site to mice iLNs along the lymphatic vessels and then to the proper aLNs after subcutaneous injection at the tail base of a mouse. Images were recorded at 6 hours after prime injection. h, hours. (D) Averaged pEr-P³-RBD signals in iLNs of mice normalized by background signals (in a region away from the LNs) plotted as a function of time after subcutaneous injection of pEr-P³-RBD vaccines. Error bars represent the SD of five repeated experiments. Data are presented as mean values ± SD.