Control of biofilm formation in water using molecularly capped silver nanoparticles.

Control of biofouling and its negative effects on process performance of water systems is a serious operational challenge in all of the water sectors. Molecularly capped silver nanoparticles (Ag-MCNPs) were used as a pretreatment strategy for controlling biofilm development in aqueous suspensions using the model organism Pseudomonas aeruginosa. Biofilm control was tested in a two-step procedure: planktonic P. aeruginosa was exposed to the Ag-MCNPs and then the adherent biofilm formed by the surviving cells was monitored by applying a model biofilm-formation assay. Under specific conditions, Ag-MCNPs retarded biofilm formation, even when high percentage of planktonic P. aeruginosa cells survived the treatment. For example, Ag-MCNPs (10 microg mL(-1)) retarded biofilm formation (>60%), when 50 percent of the planktonic P. aeruginosa cells survived the treatment. Moreover, stable low value of relative biomass has been formed in the presence of fixed Ag-MCNPs concentrations at various biofilm incubation times. Our results showed that Ag-MCNPs pretreated cells were able to produce EPS although they succeeded to form relatively low adherent biofilm. These pretreated cells appear well preserved and undamaged under TEM HPH/freeze micrographs, yet the intra cellular material seems to be pushed towards the peripheral parts of the cell, possibly indicating a survival strategy to the presence of Ag-MCNPs. The lower value of relative biomass formed in the presence of Ag-MCNPs could be associated with molecular mechanisms related to biofilm formation or continuous release of silver ions in the sample. However, further research is required to examine these factors.

Silver nanoparticle-E. coli colloidal interaction in water and effect on E. coli survival.

Silver nanoparticles exhibit antibacterial properties via bacterial inactivation and growth inhibition. The mechanism is not yet completely understood. This work was aimed at elucidating the effect of silver nanoparticles on inactivation of Escherichia coli, by studying particle-particle interactions in aqueous suspensions. Stable, molecularly capped, positively or negatively charged silver nanoparticles were mixed at 1 to 60microgmL(-1) with suspended E. coli cells to examine their effect on inactivation of the bacteria. Gold nanoparticles with the same surfactant were used as a control, being of similar size but made up of a presumably inert metal. Log reduction of 5log(10) and complete inactivation were obtained with the silver nanoparticles while the gold nanoparticles did not show any inactivation ability. The effect of molecularly capped nanoparticles on E. coli survival was dependent on particle number. Log reduction of E. coli was associated with the ratio between the number of nanoparticles and the initial bacterial cell count. Electrostatic attraction or repulsion mechanisms in silver nanoparticle-E. coli cell interactions did not contribute to the inactivation process.