Enzyme reaction controlled by magnetic heating due to the hysteresis loss of γ-Fe2O3 in thermosensitive polymer gels immobilized β-galactosidase

Control of the immobilized enzyme reaction was investigated by using a magnetic heating. β-Galactosidase and 24% γ-Fe2O3 were entrapped in a copolymer gel of N-isopropylacrylamide and acrylamide. The heat was generated inside the gel due to the hysteresis loss of γ-Fe2O3 under exposure in an alternating magnetic field (effective value 840 Oe, 2.3 kHz), and the temperature elevated above the lower critical solution temperature of the gel. The intermittent exposure of the magnetic field (0.5 min on, 15 min off) could control the temperature cycle between 20.2 and 31.4°C. The process of deswelling–swelling of the gels was repeated by the thermal cycling operation. The product concentration increased no more than 5% in the enzyme reaction. This was smaller than the result reported in the isothermal operation (heating from outside of the gel). It was considered that the hydraulic pump effect was not observed by heating from inside the gel: As compared with the isothermal operation at 31.4°C (around 4.2 kJ/h for heating the solution in the column), the thermal cycling operation was found to need less energy for intermittent heating (1.2 kJ/h) in order to keep the same conversion in the enzyme reaction.