The Benzyl-PEG-acid is synthesized by Benzyl-PEG-t-butyl. Prepared for Benzyl-PEG-PFP. It contains a carboxylic acid group on one end with either a benzyl on the other end. It has defined molecular weights and spacer lengths and is used for modifying proteins or surfaces witch containing amine groups such quantum dots, self-assembled monolayers and magnetic particles. Functionalization of solid surfaces with polyethylene glycol spacers significantly reduces nonspecific protein binding.