Fig. 3

Biodistribution and bone-targeting of P800SO3-Cl, P800SO3-SH, and P800SO3-PEG in mice. 50 nmol (2.5 mg kg⁻¹) of each NIR fluorophore was injected intravenously to 20 g CD-1 mice 4 h prior to imaging. Whole body bone imaging was conducted (a) as well as knee joint imaging (b) under color (top), NIR-I (middle), and NIR-II (bottom) channels. Scale bars = 5 mm (a) and 2 mm (b). c The SBR of each knee bone over the neighboring muscle tissue was calculated (n = 3, mean ± S.D): **p < 0.01, ***p < 0.001, ****p < 0.0001. d Caudal vertebrae were imaged under the NIR-I and NIR-II window 4 h post-injection of P800SO3-PEG. Scale bars = 3 mm. e FWHM analysis of the tail highlighted by the white dashed box in (d). Based on the cross-sectional intensity profiles in NIR-II, the length of the coccyx condyle spacings was 0.99–1.01 mm