The hybrid inorganic/organic gel with immobilized papain enzyme in micro/nano size was prepared by absorption-flocculation co-immobilization method, in which polyacrylamide (PAM) was used as the flocculation agent, and characterized by scanning electron microscopy (SEM), energy dispersive spectrometer mapping (EDS), and size analyzer. Evolution of surface Zeta potential (ZP) of nano-gel containing enzyme with pH revealed that the main interaction between the enzyme and immobilization support was electrostatic attraction. The electrostatic field generated by the surface charges exhibited major impact on the enzyme loading and particle size distribution. At pH＝7.0 and mass ratio of TiO₂ to PA＝7.5∶1, the maximum amount of enzyme loading was achieved as 121.84 mg/g, corresponding to the efficiency of 91.38%. The size of nano-gel with immobilized enzyme was about 0.444 μm and its distribution was very narrow in either low or high pH range. SEM/EDS results showed that immobilized papain was homogeneously dispersed in the porous hybrid gel. The stability test showed that the relative activity of immobilized papain still remained more than 50% even after five times cycle of reuse. It indicates that this novel method of immobilization could be propitious to the well dispersion, high stability and loading amount of papain.

Key words: Zeta potential, electrostatic interaction, inorganic-organic hybrid gel, micro/nano structure, co-immobilization