Size selection and concentration of silver nanoparticles by tangential flow ultrafiltration for SERS-based biosensors.

A proposed tangential flow ultrafiltration method was compared to the widely used ultracentrifugation method for efficiency and efficacy in concentrating, size selecting, and minimizing the aggregation state of a silver nanoparticle (AgNP) colloid while probing the AgNPs' SERS-based sensing capabilities. The ultrafiltration method proved to be more efficient and more effective and was found to tremendously boost the SERS-based sensing capabilities of these AgNPs through the increased number of homogeneous SERS hot spots available for a biotarget molecule within a minimal focal volume. Future research studies and applications addressing the physiochemical properties or biological impact of AgNPs would greatly benefit from ultrafiltration for its ability to generate monodisperse colloidal nanoparticles, to eliminate excess toxic chemicals from nanoparticle synthesis, and to obtain minimum levels of aggregation during nanoparticle concentration.