Fig. 4

PA imaging in vivo. A Merged ultrasound (US, gray scale) and PA (red-yellow scale) images of unlabeled or OSPNs+-labeled hMSCs. Images of OSPNs+-labeled cells were acquired serially at different post-injection time (days 0, 3, 6, 10, and 14). PA signals were recorded at 1064 nm (energy density: 5 mJ/cm²). Scale bar: 3 mm. B Combined US and PA imaging of unlabeled or OSPNs+-labeled hMSCs injected into the brain of nude mice using NIR-I (860 nm) or NIR-II (1064 nm) light excitation (energy density: 10 mJ/cm²). Arrow indicates the skull position. Scale bar: 3 mm. C Normalized PA SNR of OSPNs+-labeled hMSCs implanted into mice brain under NIR-I (860 nm) or NIR-II (1064 nm) light excitation (*p < 0.05). The image was reproduced from article published by Yin, Pu, Wang, Bian and co-workers in ACS Nano journal in the year 2018 [97]