One of the major factors that limits the use of membranes in many applications involving biological compounds is membrane fouling. Proteins and other biological compounds form aggregates on the membranes being used a cause a very significant permeate flux decrease. Alkanethiols with a terminal tri(ethylene glycol) functional group are well-known for their ability to prevent non-specific protein adsorption. These alkanethiols can be used to form a self-assembled monolayer on metal surfaces which in turn prevents the formation of protein aggregates on the surface. (1-Mercaptoundec-11-yl) tri(ethylene glycol) was synthesized and used to form a self-assembled monolayer on a silver membrane in an effort to decrease membrane fouling by a protein solution. The treated membrane shows a greatly decreased rate of fouling from bovine serum albumin solution with the normalized flux remaining more than 60% higher than the normalized flux of a silver membrane with no self-assembled monolayer. The rate of normalized flux decline starts to increase after approximately 70 minutes, but it still remains well above the rate for an untreated membrane even after 120 minutes.
Other terminal functional groups were studied while maintaining the carbon chain length of the alkanethiol at 11 carbons: an organic acid (11-mercaptoundecanoid acid), an alcohol (11-mercapto-1-undecanol), and an alkyl chain (1-undecanethiol). 1-Undecanethiol decreases initial normalized flux decline by as much as 25% versus a silver membrane with no self-assembled monolayer, but the flux decline does increase and offers only a 5% improvement after 120 minutes. 11-Meraptoundecanoic acid improves the normalized flux decline, but only slightly. Likewise, 11-mercapto-1-undecanol only slightly improves normalized flux decline.