Fig. (5). In vivo uptake of IRdye800 ligand in HaloTag-expressing tumor xenografts For in vivo tumor labeling with the IRdye800 ligand, NCr nude mice bearing control HCT116 (left, yellow arrow) and HCT116–HT tumors (right, blue arrow) on the flanks were intravenously injected with 0.25 mg of the IRdye800 ligand. (A) Planar fluorescence imaging was performed 1 h (day 0) and 1, 2 and 3 days after probe injection with Ex 745 nm/ Em 800 nm filters. (B) Enhanced IRdye800 fluorescence was observed in the HT-expressing tumors. (C) Quantitative analysis shows significant increase of IRdye800 fluorescence in HT-positive tumors. The left panel illustrates the fluorescence efficiency of tumors. The right panel indicates the relative S/N ratios of tumors, normalized to fluorescence at the neck as reference. (D) IRdye800 ligand uptake was observed in the gastrointestinal track as early as 2 h after injection.