Photothermal nanotherapeutics and nanodiagnostics for selective killing of bacteria targeted with gold nanoparticles.

We describe a new method for selective laser killing of bacteria targeted with light-absorbing gold nanoparticles conjugated with specific antibodies. The multifunctional photothermal (PT) microscope/spectrometer provides a real-time assessment of this new therapeutic intervention. In this integrated system, strong laser-induced overheating effects accompanied by the bubble-formation phenomena around clustered gold nanoparticles are the main cause of bacterial damage. PT imaging and time-resolved monitoring of the integrated PT responses assessed these effects. Specifically, we used this technology for selective killing of the Gram-positive bacterium Staphylococcus aureus by targeting the bacterial surface using 10-, 20-, and 40-nm gold particles conjugated with anti-protein A antibodies. Labeled bacteria were irradiated with focused laser pulses (420-570 nm, 12 ns, 0.1-5 J/cm(2), 100 pulses), and laser-induced bacterial damage observed at different laser fluences and nanoparticle sizes was verified by optical transmission, electron microscopy, and conventional viability testing.