Four series of noble networks were synthesized with acrylic acid (AAc) copolymerized with varying amount of 2-hydroxy propyl methacrylate or dodecyl methacrylate (AAc/HPMA or AAc/DMA; 5:1 to 5:5, w/w) in the presence of ethylene glycol dimethacrylate (EGDMA; 1, 5, 10, 15, and 20%, w/w) as a crosslinker and ammonium per sulfate (APS) as an initiator. Each of the networks was used to immobilize a purified lipase from Pseudomonas aeruginosa MTCC-4713. The lipase was purified by successive salting out with (NH4)(2)SO4, dialysis, and DEAE anion exchange chromatography. Two of the matrices, E-15a, i.e. [poly (AAc(5)-co-DMA(1)-cl-EGDMA(15))] and I-15c, i.e. [poly (AAc(5)-co-HPMA(3)-cl-EGDMA(15))], that showed relatively higher binding efficiency for lipase were selected for further studies. I-15c-hydrogel retained 58.3% of its initial activity after 10th cycle of repetitive hydrolysis of p-NPP, and I-15c was thus catalytically more stable and efficient than the other matrix. The I-15c-hydrogel-immobilized enzyme showed maximum activity at 65 degrees C and pH 9.5. The hydrolytic activity of free and I-15c-hydrogel-immobilized enzyme increased profoundly in the presence of 5 mM chloride salts of Hg2+, NH4+, Al-3(+), K+, and Fe3+. The immobilized lipase was preferentially active on medium chain length p-nitrophenyl acyl ester (C:8, p-nitrophenyl caprylate). (c) 2006 Wiley Periodicals, Inc.