Amine- and carboxyl-quantum dots affect membrane integrity of bacterium Cupriavidus metallidurans CH34

The present study examines the interaction of amine- and carboxyl- PEG core/shell quantum dots (QDs) with metal resistant bacterium Cupriavidus metallidurans CH34. The evolution of the number of QDs, their hydrodynamic radius, diffusion coefficients and single particle fluorescence were characterized before and during the contact with bacterium by Fluorescence correlation spectroscopy (FCS). The obtained results showed that at nanomolar concentrations the amine- and carboxyl-PEG-QDs with average hydrodynamic radiuses of 16.4 and 13.5 nm, form stable dispersions in the absence and presence of 15 mgC L- 1 HA. The decrease of the number of fluorescent particles in the bacterial medium, determined by FCS, together with the increase of the fluorescence of bacterial cells over the background, found by flow cytometry (FCM), demonstrated the association of QDs to C. metallidurans. Furthermore, QDs enhanced the level of the reactive oxygen species in the bacterial cells and augmented the percentage of the cells with damaged and leaky membranes as probed by FCM in combination with 5-(and-6)-carboxy- 2´7´- dichlorodihydrofluorescein diacetate and propidium iodide stains. No difference in the behaviour of amine- and carboxyl-PEG-QDs was found, suggesting that different functional groups in the surface coating have no effect on bacterium-QD interactions under the studied conditions. The presence of HA does not affect the hydrodynamic characteristics of the functionalized QDs, but prevented the damage to the bacterial membrane. The slight decrease in the bacterial growth found after exposure of C. metallidurans to these QDs was attributed to the nanoparticles themselves rather the cadmium, zinc or selenium ions released from the QDs.