Indocyanine green (ICG) is an organic, FDA-approved photosensitizer dye which is used for clinical optical imaging, diagnostic and treatment. To address the rapid clearance and non-specific tissue binding issues of ICG, we have developed a methodology to encapsulate ICG within stable, non-liposomal nanoparticle/polymer hollow spheres called nanoparticle-assembled capsules (NACs). To prepare ICG-containing NACs (ICG-NACs), we combined aqueous solution of ICG, polyallylamine (PAH), and phosphate anions in the proper ratios, with an aqueous suspension of 12-nm silica nanoparticles (NPs). This simple procedure was carried at room temperature and neutral pH. The ICG-NACs were recovered via centrifugation and redispersion without damage. ICG loading could be readily controlled, with an attainable maximum loading of ~52 wt%. There was negligible leakage of ICG from the capsules after 8 hours at room temperature in isotonic solution. Only 20% of ICG was lost after 8 hrs at 37 °C. These ICG-containing microcapsules should have demonstrated advantages over free ICG in phototherapy treatment.