Several methods are employed to achieve size separation of nanoparticles, each with its advantages and limitations.
Centrifugation Centrifugation leverages centrifugal force to separate particles based on their size and density. By spinning a sample at high speeds, larger and denser particles sediment faster than smaller and lighter ones. This technique is highly effective for separating nanoparticles with slight differences in size.
Filtration Filtration involves passing a nanoparticle suspension through a membrane with defined pore sizes. Particles larger than the pores are retained, while smaller particles pass through. This method is straightforward and effective but might not be suitable for very small nanoparticles or those prone to aggregation.
Size-Exclusion Chromatography (SEC) Size-Exclusion Chromatography separates particles based on their hydrodynamic volume. Nanoparticles are passed through a column packed with porous beads; smaller particles penetrate deeper into the pores and elute later than larger particles. SEC is particularly useful for separating polymers and biomolecules.
Dynamic Light Scattering (DLS) Dynamic Light Scattering measures the fluctuations in light scattering due to the Brownian motion of nanoparticles. The scattering pattern is used to calculate the particle size distribution. DLS is a rapid and non-invasive method, but it is more suited for spherical and well-dispersed particles.
Field-Flow Fractionation (FFF) Field-Flow Fractionation utilizes a perpendicular force field to a flow stream to separate particles based on their size and mobility. Types of FFF include sedimentation, flow, and electrical field-flow fractionation. This technique offers high resolution and is suitable for a wide range of particle sizes.
Electrophoresis Electrophoresis separates charged nanoparticles under the influence of an electric field. Particles move at different speeds based on their size and charge. This method is commonly used in the separation of biomolecules such as DNA and proteins.
