Pragmatic Studies on Protein-Resistant Self-Assembled Monolayers

Summary. The present study describes new synthetic routes to oligo(ethylene glycol)-terminated alkanethiols ( OEG-AT s), starting from α,ω-dibromoalkanes, which are reacted either with OEG or with trityl mercaptan in the first step. In addition to these ether conjugates of OEG and AT , analogous ester and amide conjugates were prepared by established procedures. All thiols were used to form self-assembled monolayers ( SAM s) on cleaned gold surfaces and these were stored for 1–2 weeks under water at 4°C before the extent of nonspecific protein adsorption was tested with IgG , BSA , and lysozyme at 1 mg cm −3 protein concentration in phosphate-buffered saline. Under these practice-oriented testing conditions, SAM s with tri(ethylene glycol) chains ( EG 3 ) exhibited nonsatisfactory protein resistance, in sharp contrast to EG 4 or longer OEG chains. The effectiveness of EG 3 was partially restored when they were linked to a long acyl chain (16-mercaptohexadecanoic acid) instead of 12-mercaptododecane or 11-mercaptoundecane. Furthermore it was found that (i) SAM formation at 20 μ M thiol versus 500 μ M OEG-AT gave identical results, (ii) gel-filtered proteins were much less adsorbed than the unpurified commercial products, and (iii) the method for gold-precleaning was very critical. In conclusion, this study offers convenient synthetic routes to OEG-AT and helps to choose molecules and procedures for reliable preparation of protein-resitant SAM s with prolonged stability during storage.