Immobilization of
enzymes has been widely reported due to their
reusability, thermal stability, better storage abilities, and so on.
However, there are still problems that immobilized enzymes do not
have free movements to react to substrates during enzyme reactions
and their enzyme activity becomes weak. Moreover, when only the porosity
of support materials is focused, some problems such as enzyme distortion
can negatively affect the enzyme activity. Being a solution to these
problems, a new function “floatability” of enzyme devices
has been discussed. A “floatable” micron-sized enzyme
device was fabricated to enhance the free movements of immobilized
enzymes. Diatom frustules, natural nanoporous biosilica, were used
to attach papain enzyme molecules. The floatability of the frustules,
evaluated by macroscopic and microscopic methods, was significantly
better than that of four other SiO2materials, such as
diatomaceous earth (DE), which have been widely used to fabricate
micron-sized enzyme devices. The frustules were fully suspended at
30 °C for 1 h without stirring, although they settled at room
temperature. When enzyme assays were performed at room temperature,
37, and 60 °C with or without external stirring, the proposed
frustule device showed the highest enzyme activity under all conditions
among papain devices similarly prepared using other SiO2materials. It was confirmed by the free papain experiments that
the frustule device was active enough for enzyme reactions. Our data
indicated that the high floatability of the reusable frustule device,
and its large surface area, is effective in maximizing enzyme activity
due to the high probability to react to substrates.