A polymer-free synthesis method is provided for preparation of monodisperse nanostars. The nanostars can be used for treating and imaging cells in in vivo or ex vivo. The modes of treatment include use of a nanostar modified with a photo-activatable drug, which drug is activated by the photo-response of the nanostar to electromagnetic stimulation; use of a nanostar modified with a thermally-activatable drug, which drug is activated by a thermal response of the nanostar to electromagnetic stimulation; and the thermal response of the nanostar itself to electromagnetic stimulation, which can directly or indirectly cause the death of an undesirable cell.