Plasma treatment of multi-walled carbon nanotubes for lipase immobilization

Plasma-modified multiwalled carbon nanotubes (MWNTs) were used as a support to immobilize lipase. The effects of vacuum plasma treatment power, vacuum plasma treatment time, immobilization temperature, immobilization time, and initial protein concentration of the lipase on the amount of lipase immobilized and on the subsequent activity of the immobilized lipase were investigated. The results showed that the adsorption capacity of the plasma-modified MWNTs could reach 0.15 g/g and that the maximal enzyme activity of the immobilized lipase was 520U/g under optimized conditions. Fourier transform infrared (FTIR) analysis and transmission electron microscopy (TEM) were used to characterize the properties of the plasma-modified MWNTs and plasma-modified MWNTs-lipase, and the results showed that the lipase was successfully immobilized on the plasma-modified MWNTs. Also, the MWNTs-lipase produced an esterification rate of approximately 47% in the synthesis of polyethylene glycol (PEG)-aliphatic esters.