Light-triggered Janus nanomotor for targeting and photothermal lysis of pathogenic bacteria.

The rapid photothermal lysis of Escherichia coli O157:H7 treated with light-triggered Janus nanomotors was visualized by Hilbert differential contrast transmission electron microscopy (HDC-TEM). The extraordinary advantage of this high-resolution microscopic technique was that it revealed the detailed ultrastructure alterations of the treated cells at a state close to their native one. The micrographs demonstrated that Janus nanomotors (mesoporous silica nanoparticles with gold hemisphere and half-capped with cysteamine) were able to target and bind to the pathogenic E. coli. The biorecognition reaction proceeded at slightly acid pH thankful to the formed electrostatic adhesion between positively charged amino groups on nanoparticles surface and the negatively charged cell envelope. The exposure of labeled cells to near infrared laser irradiation leaded to occurrence of effective photothermal damage of their plasma membranes, which was enough strong to lyse bacteria. It was because of the overheating obtained by the photon-to-thermal conversion reaction generated by the surface plasmon resonance response of Janus nanomotors. The good efficiency of photothermal lysis to inactivate E. coli O157:H7 was confirmed by staining with LIVE/DEAD viability kit and quantification of the few survived cells in epifluorescence microscope. Furthermore, HDC-TEM images of ice-embedded inhibited bacteria documented the labeling, membrane disruptions and lysis due to the designed operation of Janus nanomotors. The reported microscopic technique provides a novel strategy for developing of Janus nanomachines as promising platform for nondrug treatment and defeating of antibiotic-resistant pathogenic microorganisms.