Sulfo-Cy5.5-ALN is a fluorescent labeled alendronate, which targets bone. Sulfo-Cy5.5-ALN binds to hydroxyapatite and differentiated osteoblasts in vitro. Sulfo-Cy5.5-ALN selectively binds to the mineralized areas of the tumor. Sulfo-Cy5.5-ALN can be used to detect bone overgrowth in prostate bone metastasis.