A chip-calorimetric approach to the analysis of Ag nanoparticle caused inhibition and inactivation of beads-grown bacterial biofilms.

With the increasing complexity of model systems for the investigation of antibacterial effects of nanoparticles, the demands on appropriate analysis methods are rising. In case of biofilms grown on small particles, the high inhomogeneity of the samples represents a major challenge for traditional biofilm analysis. For this purpose, we developed a new calorimetric method which allows non-invasive and real-time investigation of the effects of nanoparticles on beads-grown biofilms which meets the requirements for an increased sample throughput. The method employs a newly developed chip calorimeter that is able to detect changes in the metabolic activity of biofilm samples within minutes. Using this novel device, the antibacterial effect of silver nanoparticles on Pseudomonas putida biofilms grown on agarose beads was investigated. The superparamagnetic properties of the embedded particles within the agarose beads allow an automated sample throughput. Growth inhibition and inactivation effects of silver nanoparticles (AgNPs) on biofilm bacteria were quantified by analyzing the metabolic heat production rate. As a result, a concentration dependent manner of growth inhibition and inactivation was found demonstrating the suitability and sensitivity of the methodology.