photosensitizer was investigated using variable sizes of nanoparticles either injecting the nps first and then administrating the labeled photosensitizer or postloading the labeled photosensitizer to paa nps and then perform in vivo biodistribution in mice at 24 48 and 72 h the results summarized in fig1 a 13c clearly indicate that the size of paa nps makes a significant impact in tumor enhancement experiments related to in vivo pdt efficacy of these formulations are currently in progress this invention shows the utility of porphyrin based compounds in a u201c bifunctional agent u201d for imaging breast tumor and tumor metastasis similar to most nps paa np accumulate in liver and spleen their clearance rate from most organs is significantly faster than ormosil np and they do not show long term organ toxicity even tumor avid porphyrin based ps exhibit high uptake in liver and spleen but are non toxic until exposed to light the ps clear from the system quickly days without organ toxicity however radioactive ps such as the 124i labeled analog 2 superior to 18f fdg in pet imaging of lung brain breast and pancreas tumors with a t1 2 of 4 2 days could cause radiation damage to normal organs based on the observation of high uptake of paa nps in liver and spleen below we postulated that saturating the organs with the non toxic paa nps before injecting the pet agent might reduce uptake and radiation damage by 124i imaging agent for proof of principle blank paa nps were first injected i v into mice bearing colon26 tumors followed 24 h later by i v 124i analog 100 150 u03bcci the.