) is 8.7-fold higher than AB-OMe2 (0.3 × 10 4 M - 1 cm -1 ), we anticipate this will translate into a substantially stronger PA signal. To test this property experimentally, we cast a tissue-mimicking phantom using agar and milk. Samples of AB-OMe2 or mvGlu-AB2 in water were then dosed with hemoglobin (10 mg/mL), embedded in the phantom, and imaged using a multispectral optoacoustic tomography (MSOT) imaging system (Figure and). Hemoglobin at such high concentrations was added because it is the major endogenous PA-active pigment that causes interference during in vivo imaging. The PA signal of AB-OMe2 was barely above background after unmixing; however, the corresponding PA intensity of mvGlu-AB2 was 11-fold higher at the same dye concentration (Figure ). Compared to representative strategies we have devised previously including conformational restriction (~3-4-fold) and steric relaxation (~4-fold) mvGlu is the most successful approach to date. Evaluating the Cancer Targeting Ability of mvGlu-AB2 in Live Cells Encouraged by these promising improvements, we advanced to cellular imaging to evaluate the targeting ability of mvGlu. For these experiments, we cultured A549 human lung cancer and 4T1 murine breast cancer cells because relative to their non-cancerous counterparts, GLUT1 is reported to be overexpressed by these solid tumors. First, A549 cells were stained with either AB-OMe2 or mvGlu-AB2 and imaged after 20 minutes (Figure ). The difference in signal intensity between the two conditions was dramatic, with the mvGlu-AB2-treated cells being >1000-fold brighter (Figure ). Additionally, a clear fluorescent signature was apparent even at a low dye concentration of 50 nM, indicating excellent sensitivity (Figure ). Next, we performed two complimentary experiments to assess the involvement of GLUT1. First, A549 cells were pre-incubated with glucose (15 mM), before the addition of mvGlu-AB2 (2 µM) (Figure ). The concentration of glucose was maintained throughout the duration of the experiment. We hypothesized if uptake of the dye involved GLUT1, the presence of excess glucose in the media would compete for uptake, resulting in a decrease of cellular fluorescence. This was confirmed as the signal intensity was 2fold higher when glucose was absent (Figure ). To further corroborate these results, we synthesized L-mvGlu-AB2 using L-glucose instead of D-glucose (shown in SI). Because L-glucose is not recognized by GLUT1, we anticipate that there will also be no interaction with the L-mvGlu isomer which will allow us to distinguish between nonspecific staining and GLUT1-mediated uptake. Analysis of the imaging results revealed cells treated with mvGlu prepared from the natural sugar were 3-fold brighter (Figure and). This implicates the enhancement of water solubility is likely increasing the effective dye concentration in the media (c.f. results from AB-OMe2 experiment) but ultimately, it is GLUT1 that is mediating significant dye uptake. Additional controls comparing cell permeability between ABs modified with AB-Glu1 and an oligoglycerol dendron are shown in Figure . Moreover, similar results were obtained when these experiments were performed in 4T1 breast cancer cells (Figure ).