There is an urgent need for low-cost and low-toxicity antimicrobial agents for water treatment and medical applications. Current approaches utilize relatively expensive and corrosive chemicals and disinfectants to reduce, prevent or remove biofilms in technological systems. Nanoparticle-based approaches are sought increasingly to develop disinfection systems and self-cleaning surfaces that could ‘seek and destroy’ microorganisms. In this context, the authors have developed novel lipophilic bismuth dimercaptopropanol (BisBAL) nanoparticles using a simple aqueous reduction reaction with sodium borohydride at room temperature. The objective of this study was to assess the effect of BisBAL nanoparticles on growth, attachment and biofilm formation by Pseudomonas aeruginosa. Characterization of nanoparticles showed them to be very lipophilic, with a rhombohedral crystalline structure and crystallite size of approximately 18 nm. When introduced at or above the minimum inhibitory concentration (MIC = 12·5 µM), the growth of bacteria was completely inhibited for at least 30 d. The authors show that lipophilic BisBAL nanoparticles at the MIC inhibited bacterial attachment to track-etched polycarbonate membrane surfaces and lysed bacteria embedded in biofilms, within 1 h of exposure. The authors conclude that lipophilic bismuth nanoparticles are promising antimicrobial agents, that have the capability to inhibit growth, prevent bacterial attachment to surfaces or damage existing biofilms.