Plasmonics-active metal nanostars are provided that can be used for treating and detecting cells in a subject. The modes of treatment include a photo-activated drug, which is activated by the photo-response of the nanostar to electromagnetic stimulation; a thermally-activated drug, which is activated by a thermal response of the nanostar to electromagnetic stimulation; and the thermal response of the nanostar itself to electromagnetic stimulation, which may directly or indirectly cause the death of an undesirable cell. Uptake of nanostars by undesirable cells may also aid in detection, by enhancing contrast or otherwise transforming electromagnetic stimulation during imaging.