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Tailored enzyme immobilization: engineering enzymes as application-oriented biocatalysts
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posted on 27.02.2017by Zhao, Zhengyang
Enzymes have been increasingly used as sustainable biocatalysts for a broad range of
applications ranging from manufacturing drug intermediates and functional foods to
bio-sensing in diagnostics and treating waste water. They have attractive properties
including high efficiency, strong specificity, desirable biodegradability and
renewability. For their intended applications, there are various additional attributes of
enzymes required, including thermal stability, long-term storage stability, and scalable
processability. Engineering methods such as enzyme immobilization are routinely used
to bring these required attributes. However, application-specific attributes are not
always met using generic enzyme immobilization methods.
In this work, tailored immobilization strategies have been developed to provide
application-specific attributes for enzymes, targeting three representative applications
including bio-production, diagnostics and water treatment. Through selection of the
suitable immobilization carriers and appropriate immobilization chemistries and
conditions, high performance of immobilized enzymes has been achieved for intended
applications: i) for bio-production application, the representative enzyme lipase has
been immobilized into mesoporous silica yolk/shell nanoparticles and onto solid silica
nano-spheres, respectively. The activity, stability, reusability, and selectivity of
immobilized lipase have been evaluated in both aqueous solution and organic solvent.
The immobilized lipase has shown reasonable activity and reusability in aqueous
solution. Due to the efficient protection of the silica shell, the immobilized lipase has
demonstrated excellent thermal stability and resistance to degradation by protease in
comparison to free lipase. Importantly, the immobilized lipase on silica nano-spheres
has enhanced selectivity and stability under high pressure in organic solvent, proving
the concept that tailored immobilization can indeed enhance enzyme performance
under extreme pressures. ii) for diagnostic application, the mesoporous silica nanorods
have been selected to immobilize two representative enzymes, horseradish peroxidase
(HRP) and alkaline phosphatase (ALP). The immobilized enzymes have facilitated
fabrication of the low-cost sensors in the format of low-cost bio-active papers and
printed micro-ring plates. The results have demonstrated that enzyme-based sensors
have high storage stability and delivery ability under dry state without refrigeration.
Also, micro-ring plate-based sensor has shown dual diagnostic functions in one ring
with attractive semi-quantitative diagnostic ability. iii) For environmental application,
the representative enzyme penicillinase has been immobilized on two different yet
complementary carriers - magnetic graphene oxide (MGO) and asymmetric polymer
membranes with nano-channels, respectively. The selection of MGO provides easy
recyclability of immobilized enzymes due to strong magnetic property of MGO.
Separately, the optimized dimensions of nano-channels have provided sufficient
surface area for immobilization of penicillinase while ensuring there are sufficient
reaction times for degrading the substrate (penicillin). For both carriers, the
immobilized penicillinase has shown excellent efficiency and high reusability while
offering attractive storage stability and thermal stability for degradation of penicillin.
The tailored enzyme immobilization methods developed in this work have enabled
enzymes to function under different physical states including aqueous solution, organic
solvent and dry state as required by their specific applications. The knowledge obtained
can guide tailoring immobilized enzymes to develop high-efficient and sustainable