Fig. 5

a Illustration of the preparation procedure of OSPNs\(^+\) and the  OA labelling of hMSCs after transplantation. b Merged ultrasound (US, gray scale) and OA images of subcutaneously transplanted unlabelled or OSPNs\(^+\)- labelled hMSCs (10\(^5\) cells) in vivo. Images of OSPNs\(^+\)- labelled cells were acquired serially at different post-injection time (days 0, 3, 6, 10, and 14). OA signals were recorded at 1064 nm (energy density: 5 mJ/cm\(^2\)). Scale bar: 3 mm. c Combined US and OA imaging of unlabelled or OSPNs\(^+\)- labelled hMSCs (80\(\times\)10\(^3\) cells) injected into the brain of nude mice using NIR-I (860 nm) or NIRII (1064 nm) light excitation. The energy density of the laser was adjusted to the same value at 10 mJ/cm\(^2\). Images were collected immediately after cell injection. Arrow indicates the skull position. Scale bar: 3 mm. d Normalized OA SNR of OSPNs\(^+\)- labelled hMSCs implanted into mice brain under NIR-I (860 nm) or NIR-II (1064 nm) light excitation (\(^*\)p < 0.05). Adapted with permission from [44].Copyright \(\copyright\) 2018, American Chemical Society