PA Imaging Unmixing Experiment in Tissue-Mimicking Phantoms. Tissue mimicking phantoms were prepared as reported in the SI. mvGlu-AB2 or AB-OMe2 (30 µM) were prepared in water containing hemo-globin from bovine blood (10 mg/mL). The solutions were pipetted in a plastic tube and sealed with hot glue. PA measurements were taken at 5 nm intervals (660 -850 nm). The subsequent images were spectrally un-mixed using the iThera Invision software with spectra of hemoglobin and the PA spectra of mvGlu-AB2 and AB-OMe2. The resulting values at the λPA are reported as the mean PA signals (Mean Pixel Intensity, MSOT a.u).