Fig. 4

In vivo multi-spectral optoacoustic tomography (MSOT) imaging. a 4T1 tumour-bearing mice were given a single injection of phosphate-buffered saline (PBS) (n = 3) or 150 µg of OMV^WT (n = 4) or OMV^Mel (n = 4) via the tail vein. Tumour-specific accumulation over time was monitored using a commercially available preclinical MSOT system. Scale bar, 4 mm. OMV, outer membrane vesicle. b Melanin concentration in the tumour was measured over time. A single mean value was calculated over the tumour region. Mean values and error bars were expressed as mean ± SD, inter-group differences were assessed for significance using the paired t-test compared to control and differences were considered significant if ***p < 0.001. c, d Optoacoustic spectra from the tumour region of animals treated with c PBS or d OMV^Mel