The invention provides a nanoparticle composition that is decorated with a urea-based small-molecule peptidomimetic inhibitor of prostate specific membrane antigen (PSMA), which is expressed by almost all solid tumors. This strategy takes advantage of both the avidity of the functionalized nanoparticle for binding to PSMA and the ability of the nanoparticle to be retained for longer periods of time in the tumor due to enhanced leakage via EPR into the tumor interstitium and poor clearance due to underdeveloped or non-existent lymphatics within the tumor.