Attachment of functionalized poly(ethylene glycol) films to gold surfaces

The attachment of linear poly(ethylene glycol) (PEG) molecules (MW = 2000-5000) to gold surfaces via orthopyridyl-disulfide (OPSS) terminal groups has been studied with X-ray photoelectron spectroscopy (XPS), time-of-flight secondary ion mass spectrometry (TOF-SIMS), and surface plasmon resonance (SPR). The molecules examined included a PEG molecule terminated with a methoxy group and derivatized with an OPSS group at the other end (M-PEG-OPSS), a PEG molecule derivatized with OPSS at both ends (PEG-(OPSS)(2)), and a PEG derivatized with an N-hydroxysuccinimide group at one end and an OPSS group at the other (NHS-PEG-OPSS). Exposure of gold to aqueous solutions of these resulted in immobilization via gold-thiolate bonds from the OPSS disulfide groups. The resulting mixed PEG-/OPS-thiolate monolayers were not always in 1:1 ratio. Most of the PEG-(OPSS)(2) molecules formed gold-thiolate bonds at both ends, but some left a free, intact OPSS group. For biosensor applications, this or the free NHS groups in the NHS-PEG-OPSS films can be used to immobilize biomolecules with accessible cysteines or lysines via formation of disulfide bonds or amide bonds, respectively. The PEG films formed by M-PEG-OPSS and PEG-(OPSS)(2) resist the adsorption of albumin.