Peroxidase-like behavior and photothermal effect of chitosan-coated Prussian-blue nanoparticles: dual-modality antibacterial action with enhanced bioaffinity†
We have probed the antibacterial potential of Prussian blue nanoparticles, without (PB) and with (CHPB) chitosan-coating. Both these nanoparticles showed peroxidase-like behavior by degrading hydrogen peroxide and generating toxic reactive oxygen species (ROS). The nanoparticles also showed a photothermal effect by generating heat (hyperthermia) upon activation with 635 nm laser light. The antibacterial activity resulting from the combined peroxidase-like behavior and photothermal effect of these nanoparticles was explored in both Gram-positive and Gram-negative bacteria. It was observed that CHPB nanoparticles showed much higher antibacterial activity than PB nanoparticles, which is attributed to the favorable electrostatic interaction at the nanoparticle–bacteria interface upon chitosan coating. Further light activation led to enhanced antibacterial action, with near-complete bacterial cell death observed at CHPB treatment concentrations of 75 μg ml−1 for Gram-negative bacteria and 125 μg ml−1 for Gram-positive bacteria. The mechanism of antibacterial action of the nanoparticles was also explored though a series of assays, such as electron microscopic analysis of nanoparticle–bacteria binding, membrane depolarization, protein leakage, intracellular ROS generation, etc. Based on these studies, we conclude that CHPB nanoparticles act as robust dual-modality antibacterial agents with enhanced affinity at the nanoparticle–bacteria interface.