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.