Quantitation of IgG protein adsorption to gold nanoparticles using particle size measurement

The attachment of proteins, and other biomolecules, to nanoparticles is of critical interest both in the development of medical products using nanoparticles and in understanding the behaviour and fate of nanoparticles in biological systems. Measuring the amount of protein attached to the particles is a fundamental step in these regards and there are a variety of methods available for this purpose. In this work, we compare the use of three methods which measure particle diameter: Dynamic Light Scattering (DLS), Nanoparticle Tracking Analysis (NTA) and Differential Centrifugal Sedimentation (DCS). The choice of gold particles also permits measurement of the amount of adsorbed protein through a shift in plasmon frequency in UV-visible spectroscopy. When the protein layer is complete, the results from all methods are consistent to within similar to 20% scatter and suggest that IgG adsorption on these 20 nm to 80 nm nanoparticles is rather similar to adsorption on flat gold surfaces with a water content of similar to 60% by volume. We note an excellent correlation between plasmon frequency shift and DCS sedimentation times which indicates that both DCS and analytical ultracentrifugation can provide precise measurement of the thickness of complete protein shells on dense nanoparticles, but also show that these methods will fail for particles with a density of similar to 1.38 g cm(-3). In the low protein coverage regime, the measured amount of protein depends upon the technique: NTA and DLS provide, as expected, similar values that also correlate well with plasmon frequency shift. DCS analysis underestimates protein shell thicknesses in this regime and this may be explained through redistribution of the protein shell which reduces the frictional force during sedimentation. Crown copyright (C)2013. Reproduced with the permission of the controller of HMSO.