Encapsulation of lactate dehydrogenase in carbon nanotube doped alginate–chitosan capsules

Alginate–chitosan shell–core (AC) capsules doped with carbon nanotubes (CNTs) were prepared for lactate dehydrogenase (LDH, EC 1.1.1.27) encapsulation to convert pyruvic acid to lactic acid coupling with the oxidation of NADH to NAD+. LDH was entrapped within the liquid core of the capsules and the CNTs were incorporated in the alginate or chitosan matrices or both. The physical properties of the capsules and the immobilized LDH activity were investigated. The AC capsules doped with CNTs showed better mechanical strength than that without CNTs. The LDH loading efficiency of the AC capsules with CNTs (10 mg/mL) doped in both the shell and the core was 30.7% higher than that without CNTs. The optimal pH value for the bioconversion catalyzed by immobilized LDH was 7.0, lower than that by free LDH (7.5). The optimal temperature was 35 °C for both immobilized and free LDH. Operational stability of the immobilized LDH was greatly improved by doping CNTs in AC capsules. The results showed that this method was efficient for enzyme encapsulation in the biotechnology applications.