Helping nano-entities discover their nano-identity

Having a polydisperse nanomaterial? Nanoparticles are often characterized by techniques such as dynamic light scattering (DLS) and/or imaging methods such as transmission electron microscopy (TEM) and scanning electron microscope (SEM).

The suitability of these methods to measure polydisperse samples is sometimes questioned because they have considerable draw backs such as extreme bias towards small numbers of larger particles (DLS) or deriving measurements from a small number of particles (TEM). However, asymmetric flow field flow fractionation (AF4) is a suitable technique to measure complex sample (samples containing one or more type of analyte), and being a separation technique it gives the opportunity to collect different sub-fractions from the sample for further analysis. AF4 is quickly being recognized as the technique of choice for detailed particle analysis among those working in the nano area.

At SOLVE we have many years of experience characterizing nanoparticles such as gold and silver nanoparticles, silica and amorphous silica, core-shell nanoparticles, coated nanoparticles, iron oxide nanoparticles, non-spherical nanoparticles and environmental colloids. Here is an example of a multicore magnetic nanoparticle with a relatively broad size distribution characterized with DLS and AF4.

The size distribution by intensity obtained from DLS (Fig. 1) overestimated the size distribution towards larger sizes when compared to measurements done in AF4 (Fig. 3). When using AF4, three populations were visible in the elution profile (Fig 2), suggesting a core particles without coating (I) coated nanoparticles (II) and particle aggregates (III), while DLS showed only one population. Additionally, the conformation parameter (rrms/rh) was determined from AF4 to be about 0.75, suggesting spherical dense particles.

Figure 1. DLS: Hydrodynamic diameter of multicore magnetic nanoparticle by intensity.

Figure 2. AF4: Elution profile of multicore magnetic nanoparticle showing differential refractive index signal (blue), light scattering signal (red), and hydrodynamic diameter (green).

Figure 3. AF4: Hydrodynamic diameter of multicore magnetic nanoparticle obtained from elution time