We have investigated the most efficient way of preparing biocompatible gold nanorods (GNR) used as tool for cancer imaging and therapy. The surface of cetyltrimethylammonium bromide-stabilized gold nanorods (GNR-CTAB) was functionalized with various thio-polyethylene glycols of the general formula HS-PEGmX (m = 356-10,000; X = -OMe, -NH2). The influence of several parameters such as PEG chain length, reaction conditions and purification method on long-term stability, morphology and optical properties of the produced GNR-S-PEGmX was studied, demonstrating the existence of a threshold HS-PEGmX chain length (with molecular weight m >= 2000) for efficient steric stabilization of GNR. Several purification techniques were compared: dialysis, centrifugation and a rarely used technique in this field, size exclusion chromatography. While a very weak efficiency of dialysis was evidenced, both centrifugation and size exclusion chromatography were found to provide pure GNRs, though the latter method yielded nanoparticles with a significantly higher stability. Finally, the long-term stability of the produced GNRs was investigated in various media: water, PBS buffer and serum. (C) 2011 Elsevier Inc. All rights reserved.