An experimental study on sterile filtration of fluorescently labeled nanoparticles – the importance of surfactant concentration

Nanoparticles have attracted considerable attention in the field of separation science, especially for filtration studies designed to evaluate membrane integrity, investigate membrane pore-size properties, and model membrane transport. A common reason for studying nanoparticle filtration is their potential to be used as surrogates for the various types of viruses in water treatment and bioprocessing applications. Although the effect of adding surfactants to stabilize nanoparticle suspension has been explored for a number of different applications, there is significant variation in the amounts and types of surfactants used in those studies. In this study, we used three different sizes (59, 188, and 490 nm) of spherical fluorescent polystyrene nanoparticles (PNPs) – the two smaller sizes were chosen to mimic the width and length of Rhabdovirus, a bullet-shaped enveloped virus that is currently being studied as bio-therapeutic for the treatment of cancer. The PNPs were suspended in solutions with varying concentrations of the nonionic surfactant Tween 20 (0.0005% to 0.1% (v/v) in carbonate buffer solution) and were tested in constant-flux filtration studies using two commercial microfiltration membranes (Durapore PVDF and MiniSart PES) with 0.22 µm pore size ratings. Our results clearly show that the transmission behavior of PNPs is critically dependent on the surfactant concentration in the buffer feed solution. The results could only be partially explained by interparticle interactions as we also observed major differences in the performances of the two microfiltration membranes.