Fluorophore and its solubility in water

[Hanane]

Hi,

I have been learning new things about Fluorophores (photosensitizers) and how they get conjugated to antibodies for cancer therapy (photodynamic therapy).
And I have read something that I didn't understand: it says that the Fluorophore should be water soluble to be used in this kind of therapy (photodynamic therapy), but I don't understand why?

What's the point of its water solubility?
And what does it have to do with the effectiveness of photodynamic therapy?
And what would happen if it wasn't water soluble?

Any question that can be answered by you, I would be very thankful, cause I've been struggling to understand.
Thanks a lot in advance.

[CharonY]

Think about what PDT is used for and where the drug would be delivered to. Specifically think about how the drug is delivered to its target and where low water solubility can cause problems.