Immobilization of β-galactosidase on surface modified cobalt/multiwalled carbon nanotube nanocomposite improves enzyme stability and resistance to inhibitor.

The present study aimed to work out a high yield procedure for immobilization of Aspergillus oryzae β-galactosidase on polyaniline cobalt multiwalled carbon nanotubes nanocomposite (PANI/Co/MWCNTNC) by physical adsorption and covalent attachment via glutaraldehyde. The binding was confirmed by scanning and transmission electron microscopy along with Fourier transform-infrared spectroscopy. The immobilization yields obtained for adsorbed and cross-linked enzymes were 93% and 97%, respectively. The covalently immobilized enzyme was remarkably more stable at extremes of pH and temperature compared to native and adsorbed enzymes. The Ki values were found to increase ten-folds for covalently immobilized β-galactosidase indicating that this immobilized enzyme was markedly more resistant to galactose inhibition. The covalently attached enzyme retained 92% activity after its 10th successive reuse compared to the adsorbed β-galactosidase which exhibited 74% of its initial activity. Furthermore, no significant change was noticed in the band intensity of pBR322 plasmid when exposed to free and bound nanocomposite. The covalently bound enzyme exhibited superiority in terms of stability and reusability when compared to the adsorbed and native β-galactosidase. The results, presented here demonstrate an efficient method of immobilization of β-galactosidase on PANI/Co/MWCNTNC in order to construct a convenient and novel biosensor for the detection of lactose concentration.