Ethylene glycol monolayer protected nanoparticles for eliminating nonspecific binding with biological molecules.

The usefulness of the hybrid materials of nanoparticles and biological molecules in many occasions depends on how well one can achieve a rational design based on specific binding and programmable assembly. Nonspecific binding between nanoparticles and biomolecules is one of the major barriers for achieving its utilities in a biological system. In this paper, we demonstrate a new approach to eliminate nonspecific interactions between nanoparticles and proteins by synthesizing ethylene glycol protected gold nanoparticles. We discovered that with the water content optimized in the range of 9-18% in the reaction mixture, di-, tri-, and tetra(ethylene glycol) protected gold nanoparticles Au-S-EGn (n = 2, 3, and 4) could be directly synthesized. These gold nanoparticles that are bonded with a uniform monolayer with defined length varying from 0.8 to 1.6 nm (from molecular modeling) have great stability in aqueous solutions with a high concentration of electrolyte and organic solutions. Using ion-exchange chromatography and gel electrophoresis, we demonstrated that these Au-S-EGn (n = 2, 3, or 4) nanoparticles have complete resistance to protein nonspecific interactions. These types of nanoparticles provide a fundamental starting material for designing hybrid materials composed of metallic nanoparticles and biomolecules.