Protein decorated nano-polystyrene beads: an update about their size and density

The bio-non/bio interfaces is one of the key aspects in the development of nanotechnology applications both for biomedical applications and for understanding their behaviour in the environment where they could contribute to pollution. Protein adsorption onto synthetic polymer nanoparticles, a spontaneous, highly favorable process, is likely a mix of physical (electrostatic, hydrophobic, dispersion, etc.) and chemical interactions (hydrogen bonds, π-π stacking). In this work, we focus on the adsorption of immunoglobulin proteins of type E onto synthetic polymer nanoparticles (polystyrene - PS), a versatile platform for developing imaging and drug delivery applications. PS particles of 100 nm and 196 nm were accurately size characterized with two separation techniques, centrifugal liquid separation (CLS) and centrifugal field flow fraction (CF3), before and after coating them with a layer of antibodies against immunoglobulins of type E (aIgE), giving to the particle a specific functionality. Particle sizes were also measured with Dynamic Light Scattering (DLS), used either as stand-alone instrument and on-line linked CF3 detector (CF3-DLS). The complementary information obtained from the CLS and CF3-DLS measurements allowed the estimation of the density of the aIgE shell. The proteins immobilized at the surface fully retained their activity, as proven by the reactions between the functionalized PS-aIgE particles and immunoglobulins of type E (IgE) dispersed in suspensions prepared on purpose. The aim of this study differed from previous ones since it seeked to compare the capabilities of the two separation techniques, both based on centrifugal field (CLS and CF3), to measure the amount of aIgE adsorbed and to identify the formation of aggregates during the experiments.