Properties of Silver and Copper Nanoparticle Containing Aqueous Suspensions and Evaluation of their <i>In Vitro </i>Activity against <i>Candida albicans </i>and <i>Staphylococcus aureus </i>Biofilms

Abstract

Most microorganisms grow on surfaces as biofilms rather than as individual planktonic cells, and cells within biofilms show high levels of resistance against antimicrobial drugs. Thereby biofilm formation complicates treatment and contributes to high morbidity and mortality rates associated with infections. This study explores the physical, optical, and nano-structural properties of silver and copper nanoparticles dispersed in aqueous suspensions (nanoparticulate colloidal water) and examines their in vitro activity against microbial biofilms. Silver and copper nanoparticulate colloidal water of various concentrations were prepared and studied. Their surface energies, surface charge and surface plasmonic resonance properties were determined using contact angle measurement, zeta potential measurement and optical spectrometry, respectively. A model of biofilm formation on the wells of microtiter plates was used to determine the activity of the nanoparticulate suspensions against fungal and bacterial biofilms. Scanning electron microscopy (SEM) was used to observe the nanoparticle interactions with microbial cells within the biofilms. Results show that silver nanoparticle-containing liquids have higher surface energy than their copper counterparts; and that the surface energy increases as the concentration of silver nanoparticles increases. Altogether, the effectiveness of silver nanoparticle colloidal suspensions in controlling biofilm formation is observed and reported. For a given size of silver nanoparticles studied, it is found that the effective concentrations against microbial biofilms are far lower than their cytotoxic concentrations, indicating an overall safety and a good therapeutic index thus substantial application potential.