Bactericidal activity of gold and silver nanoparticles in solution and supported on polyhihydroxybutyrate nanospheres

This work presents the effect of Polyhydroxybutyrate nanospheres (PHB-NSs) on the bacterial activity of plasmonic nanoparticles (NPs). The PHB-NSs were used as a substrate for the metal-NPs. Silver and gold NPs in colloidal solution were synthesized by chemical reduction, while PHB-NSs were synthesized by a physical method. A normal size distribution around 27 and 208 nm characterizes gold and PHB colloids, respectively. The Ag-NP colloid has a size distribution with a positive skewness and a mean size of ~19.6 nm. Ag-NP surface plasmon resonance is 400 nm, and Au-NP is 526 nm. A resonance shift is observed when the metal-NPs are on the PHB-NSs. Numerical calculations based on the discrete dipole approximation theory provide insight into the resonance position of the composite as a function of the nanoparticle concentration. The bactericidal effect on the viability of Escherichia coli and Staphylococcus aureus strains was evaluated. Ag-NPs were more effective against E. coli than Au-NPs, while the latter were more effective against S. aureus than the former. Interestingly, the PHB-NSs caused a delay in the bacterial activity of both metal-NPs. We proposed a model to explain this delay and the increase in contact time.