Folate receptors (FRs) are membrane proteins involved in folic acid uptake, and the alpha isoform (FR‐α) is overexpressed in ovarian and endometrial cancer cells. For fluorescence imaging of FRs in vivo, the near‐infrared (NIR) region (650–900 nm), in which tissue penetration is high and autofluorescence is low, is optimal, but existing NIR fluorescent probes targeting FR‐α show high non‐specific tissue adsorption, and require prolonged washout to visualize tumors. We have designed and synthesized a new NIR fluorescent probe, FolateSiR‐1, utilizing a Si‐rhodamine fluorophore having a carboxy group at the benzene moiety, coupled to a folate ligand moiety through a negatively charged tripeptide linker. This probe exhibits very low background fluorescence and afforded a tumor‐to‐background ratio (TBR) of up to 83 in FR‐expressing tumor‐bearing mice within 30 min. Thus, FolateSiR‐1 has the potential to contribute to the research in the field of biology and the clinical medicine.

Si-Rhodamines are bright fluorophores with red to near-infrared (NIR) emission, and are widely used for fluorescence imaging of biological phenomena. Here, in order to extend the scope of Si-rhodamine fluorophores, we established a versatile synthesis of unsymmetrical Si-rhodamines. To illustrate its value, we used one of these new fluorophores to synthesize a far-red to NIR fluorescence probe for hypoxia, and showed that it can visualize hepatic ischemia in mice in vivo.

Fluorescence probes that can detect pH are useful tools for biological research and clinical diagnosis. Here we report pH-activatable near-infrared fluorescence probes, based on hydroxymethyl germanium-rhodamine (HMGeR), that are suitable for a range of biological applications. The pK a , the ratio of the fluorescent form in an acidic environment, and the absorption/emission wavelengths can all be conveniently optimized. The most promising probe, 2-HM IGeR, offers significant advantages over currently available near-infrared pH probes, notably high quantum efficiency, appropriate pK a value for biological applications, and high photostability. Further, our molecular design strategy allows easy conjugation of the probes to biomolecules without loss of functionality. We illustrate the value of this strategy by developing probe-Herceptin® and probe-avidin conjugates to visualize pH change in cellular vesicles during endocytosis, and to visualize tumors in a mouse model, respectively. We believe 2-HM IGeR is currently among the best-in-class pH-activatable near-infrared probes for biological and medical research.

Ca2+ is one of the most important second messengers in cells. A far-red to near-infrared (NIR) Ca2+ fluorescent probe is useful for multi-color imaging in GFP or YFP-expressing biosamples. Here...

Folate receptors (FRs) are membrane proteins involved in folic acid uptake, and the alpha isoform (FR‐α) is overexpressed in ovarian and endometrial cancer cells. For fluorescence imaging of FRs in vivo, the near‐infrared (NIR) region (650–900 nm), in which tissue penetration is high and autofluorescence is low, is optimal, but existing NIR fluorescent probes targeting FR‐α show high non‐specific tissue adsorption, and require prolonged washout to visualize tumors. We have designed and synthesized a new NIR fluorescent probe, FolateSiR‐1, utilizing a Si‐rhodamine fluorophore having a carboxy group at the benzene moiety, coupled to a folate ligand moiety through a negatively charged tripeptide linker. This probe exhibits very low background fluorescence and afforded a tumor‐to‐background ratio (TBR) of up to 83 in FR‐expressing tumor‐bearing mice within 30 min. Thus, FolateSiR‐1 has the potential to contribute to the research in the field of biology and the clinical medicine.