A series of 23 nitroxides () was tested for biofilm modulatory activity using a crystal violet staining technique. 3-(Dodecane-1-thiyl)-4-(hydroxymethyl)-2,2,5,5-tetramethyl-1-pyrrolinoxyl () was found to significantly suppress biofilm formation and elicit dispersal events in both Pseudomonas aeruginosa and mixed-culture biofilms. Twitching and swarming motilities were enhanced by nitroxide , leaving the planktonic-specific swimming motility unaffected and suggesting that the mechanism of -mediated biofilm modulation is linked to the hyperactivation of surface-associated cell motilities. Preliminary structure-activity relationship studies identify the dodecanethiyl chain, hydroxymethyl substituent and the free radical moiety to be structural features pertinent to the anti-biofilm activity of .