Engineering polyelectrolyte multilayer coatings as a strategy to optimize enzyme immobilization on a membrane support

This study presents a systematic design of a biocatalytic membrane reactor, where we combined physical adsorption and chemical conjugation of Alcohol Dehydrogenase (ADH) in a novel type of polyelectrolyte (PE) layer-by-layer (LbL) assembly system. The hybrid LbL structure is proposed as a strategy to simultaneously advance activity and operational stability of enzymes immobilized on a membrane surface. Using poly(allyl-amine hydrochloride) (PAH) and poly(methacrylic acid) sodium salt (PMAA) allowed functionalization of pol-ysulfone (Psf) membrane for subsequent ADH immobilization with no resistance to substrate mass transfer and no decrease in water permeability (WP) (56.5 +/- 8.8 Lm-2h -1bar- 1) compared to the pristine membrane (50.8 +/- 1.7 Lm- 2h-1bar- 1). Tailoring membrane surface chemistry, enzyme concentration, time, and pH during the adsorption step allowed to increase specific activity of the biocatalytic membrane from 1.13 +/- 0.18 mU/cm2 for immobilization on the pristine membrane to 4.09 +/- 0.53 mU/cm2 for immobilization on a PAH-modified coating. Conjugation of adsorbed ADH with PMAA layer improved reusability compared to the non-conjugated membrane (by retaining 73.4 +/- 3.2% of the starting activity on the third conversion run against 58.7 +/- 2.4%) and shifted pH optimum by 1 unit compared to the free ADH. The presented approach of LbL assembly synthesis provides a potential foundation for engineering of biocatalytic nanoscale reactors.