Rational design of multi-functional gold nanoparticles with controlled biomolecule adsorption: a multi-method approach for in-depth characterization.

Multi-functionalized nanoparticles are of great interest in biotechnology and biomedicine, especially for diagnostic and therapeutic purposes. However, at the moment the characterization of complex, multi-functional nanoparticles is still challenging and this hampers the development of advanced nanomaterials for biological applications. In this work, we have designed a model system consisting of gold nanoparticles functionalized with two differentially-terminated poly(ethylene oxide) ligands, providing both "stealth" properties and protein-binding capabilities to the nanoparticles. We use a combination of techniques (Centrifugal Liquid Sedimentation, Dynamic Light Scattering, Flow Field Flow Fractionation, Transmission Electron Microscopy, and Circular Dichroism) to: (i) monitor and quantify the ratios of ligand molecules per nanoparticle; (ii) determine the effect of coating density on non-specific protein adsorption; (iii) to assess the number and structure of the covalently-bound proteins. This article aims at comparing the complementary outcomes from typical and orthogonal techniques used in nanoparticle characterization by employing a versatile nanoparticle-ligands-biomolecule model system.