The stability of α-methoxy-ω-mercapto-poly(ethylene glycol) (mPEG-SH, MW 5000) modified gold colloids was investigated, and the corresponding stability mechanism was preliminarily interpreted. Linear mPEG-SH molecules were chemically bonded to gold particle surfaces via the end group, SH, forming polymer brush-coated gold colloids. Experimental results indicate that the PEG-modified gold colloids can resist aggregation under rigorous conditions of pH＝1～13.5 or salt concentration as high as 1.20 mol/L. It is because that the adsorbed PEG layer provides steric stabilization for the gold colloids instead of their original DLVO stabilization (viz. charge stabilization). Therefore, the PEG layer-coated gold colloids largely overcome the problems associated with DLVO-stabilized colloids, such as susceptivity to environment conditions and easiness in aggregation, and can survive in complex conditions (e.g. physiological conditions). Because of the water soluble, nontoxic, and biocompatible properties of PEG, the gold nanoparticle/PEG conjugates with high stability possess the excellent properties of both gold nanoparticles and PEG and can serve as bio-nanoprobes for bio-analysis.

Key words: gold colloid, thiolated PEG, DLVO stability, steric stability