Clearly, the hybrid of photocage and transporter enabled cellular uptake of ATP with different but distinct subcellular localizations. We were hence interested to also study organismal uptake and distribution since covalent tethering of transporters should in principle enable deep tissue penetration for diverse in vivo applications. Therefore, the tissue penetration of (G1-NH2-) 19, (G1-guanidine-) 20, (G2-NH2-) 21, (G2-guanidine-) 22 was investigated using zebrafish embryos as a model organism. Initially, we focused on 1-day old embryos, a developmental stage when the heart beats and muscles begin to contract. Compounds were added to dechorionated embryos, and after 24 h or 48 h incubation time distribution of compound fluorescence was investigated. Larvae were washed and imaging performed using a laser scanning confocal microscope. We decided to image the head of the embryo, because its diameter of 500 µm enables to observe deep tissue penetration, and compound distribution in brain and retina may be analyzed. In addition, the epithelium of the nasal placode is directly exposed to compounds in the medium. Compared to the negative control, enhanced fluorescence from the nasal placode of zebrafish was first observed when (G1-NH2-) 19