Fig. 6

A The US (grey), PA (green), and their overlay coronal sections of brain of control model (top) and tumor model (bottom) before and after tail vein injection of 250 µL of 250 nM PDI NPs. B The relative PA signal changes of the skull region (S, in red dotted circle of A) and tumor region (T, in blue dotted circle of A at 2 d compared with that at 1 d, respectively, and that of T/S at 1 d and 2 d. C PA spectra of PDI NPs in aqueous solution (black line), the region in red dotted circle of A before injection of NPs (red line) and tumor region of A after 2 d injection of NPs (blue line). D The PA coronal sections of PDI NPs with different concentrations (from 50 to 0.390625 nM) in agarose gel (in vivo phantom). E The plots of PA intensity–NP concentration and PA detectable depth–NP concentration relationships. The image was reproduced from article published by Fan, Cheng and co-workers in Advanced Materials journal in the year 2015 [111]