Enzymatic catalysis, using microreactors, has gathered a lot of interest within the scientific community, due to its high specific surface which allows for heat and mass transfer processes and the controllability of reaction parameters within the microreactor.
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A team of Researchers from China have now developed a new approach using immobilized enzymes on an unsinkable graphene sheet, in the hope of alleviating some of the problems with current microreactors.
Microreactors are now used for many biocatalytic reactions as they possess an extremely high surface-to-volume ratio due to their specific geometrical features. This in itself brings extra benefits such as a larger specific surface area for heat and mass transfer processes in a short time frame, and is one of the main reasons as to why they are used. The parameters within these microreactors are also very controllable, which is a key consideration due to the amount of heat fluctuation generated in the reactions.
Biocatalytic reactions in microreactors are currently used for a range of uses, including heterogeneous catalysis, homogeneous catalysis and photocatalysis. However, current microreactors do suffer from some drawbacks in that it is difficult to separate the free enzyme from the product, you can’t reuse the enzyme and it is easy for the enzyme to become inactive within the microchannel.
Researchers have turned to immobilizing enzymes onto a substrate in an attempt to address some of the challenges faced in microreactor technologies. There have been many variations of immobilized enzyme substrates produced.
Whilst some have addressed the challenges faced within the microreactor, they have also brought upon new challenges, namely the issue of coagulation of the immobilized enzymes on the nanoparticles and the high loading for enzymes.
Carbon nanomaterials, especially graphene, have been touted as the next possible material to address the challenges induced by both the microreactor and the immobilization process. Realizing this, the Researchers from China have now utilized a mobile and unsinkable fictionalized graphene sheet, immobilized with the naringinase enzyme, to produce isoquercitrin in a microreactor.
To characterize the immobilized graphene sheets, and the final product, the Researchers used a combination of X-ray diffraction (XRD, SHIMADZU XRD-6000X), Fourier-transform infrared spectroscopy (FTIR, BRUKER TENSOR 27), scanning electron microscopy (SEM, HITACHI S-4700), fluorescence inversion microscopy (Nikon ECLIPSE TS100), high performance liquid chromatography (HPLC, H&E Pump P3000A) with an Ultraviolet-Visible detector (UV-Vis, PLC-2, Biochem. Jinda Ltd) and a Alltima C18 column (W. R. Grace & Co).
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The Researchers found that the reaction of nanringase to isoquercitin produced excellent results, with a yield of 92.24 ± 3.26% being obtained within 20 minutes of the reaction starting in the microreactor channel.
The Researchers also successfully achieved 10 cycles of an enzymatic hydrolysis reaction and maintained and enzyme activity of at least 85.51 ± 2.76% throughout the whole reaction.
The results also showed great promise against larger scale reactors, namely batch scale reactors, as this reaction was shown to have a kinetic parameter 1.9-fold greater than batch reactors. This is in addition to the reaction time being 2/3 of batch reactor experiments.
The results have shown that the immobilization of enzymes onto a mobile and unsinkable, graphene sheet produced a high persistent specificity and mild catalytic characteristics, which enabled the enzyme to be used multiple times. Such issues have been a challenge for the microreactor field, but by using this method, the Researchers have managed to negate the problems associated with both the microreactor and the immobilization process.
These findings, especially the recyclability of the enzyme, will be a huge cost-saver for the enzyme catalysis applications and will likely be replacing current, problem-ridden, methods seen with microreactors today.
Sources and Further Reading
- “Moving and unsinkable graphene sheets immobilized enzyme for microfluidic biocatalysis”- Gong A. et al, Scientific Reports, 2017, | DOI:10.1038/s41598-017-04216-4
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