The development of nanotechnology and the growing use of metallic nanoparticles (NPs) for biological applications has raised great concern over its safety and impact on human health. In biological media NPs can suffer different transformations (i.e. agglomeration/aggregation, ion release or protein corona formation) which modify their physico-chemical properties [1]. Among them, electrical parameters (electrophoretic mobility (µ), and surface charge (ζ-potential)) are critical because they determine the NP-biomolecules interactions, and NP stability. Until now, different batch techniques, such as dynamic and electric light scattering (DLS/ELS), have been used for this purpose, but the high polydispersity and size distribution make difficult the analysis. For this reason, separation techniques are needed to isolate the NPs and improve the study of their transformations in these types of media.

A promising option is electrical asymmetrical flow field-flow fractionation (EAF4). This separation technique is a result of the combination of a regular cross flow with an electric field in the separation channel [2]. EAF4 allows the size-resolved determination of µ and ζ-potential in contrast with batch measurements. It can be hyphenated to different detectors, but inductively coupled plasma mass spectrometry (ICP-MS) increases the specificity, provides NP-concentration detection limits down to biological relevant levels, and even allows the detection of the ionic forms. However, up to now the EAF4-ICP-MS option has been under-exploited.

Thus, the aim of this work has been to develop, optimize and apply a new analytical strategy via EAF4-ICP-MS for the study of the gold (AuNP) and platinum (PtNP) NPs in complex biological media, such as bovine serum albumin, fetal bovine serum (FBS), and cell culture media (Dulbecco's Modified Eagle Medium, DMEM). Results for both NPs showed an increase in their hydrodynamic diameter while they were dispersed in these media. Also, it was noted an effect onto µ and ζ-potential of the NPs towards more positive values because of their instability. Furthermore, changes in these parameters were more notable when the complexity of the media increased. In addition, an oxidation process was found in the specific case of AuNPs.

This work demonstrates the great potential of EAF4-ICP-MS to simultaneously evaluate changes in a size-resolved mode of the electrical and physical-chemical properties of AuNPs and PtNPs while they are dispersed in complex biological matrices and will be further applied in toxicological studies.