Given that our integrative system has been proved to produce hydrogen with great stability and repeatability and its intrinsic characteristics for scalable production, we think our project is a successful applied design. Here, we summarize the qualification and merits of our design in the following figure. In addition, biofilm-interfaced Nanorods has the potential for easy recycling and is cheap for production, thus presenting an innovative and interesting example towards industrial-oriented artificial photosynthesis system.
Figure 1 Apparatus of the hydrogen production assay.
Figure 2 Hydrogen evolution curve with nanorods bound to biofilm beads.During the period with lighting, the hydrogen production increases, until we shut off the light at points that correspond to the tips. The curve then goes downward, showing that the hydrogen concentration is lowered, an evidence of the bidirectional catalytic activity of hydrogenase. It is noteworthy that the hydrogenase shows the greatest production rate at the beginning of lighting: a transient sharp rise can be observed at the valleys. It is also obvious that each period of “light-on light-off” gives similar curves, which implies that our hydrogenase is stable. In our experiment, we find that despite the reported affected catalytic ability of FeFe hydrogenase due to oxygen, non-strict anaerobic and short-term exposure to oxygen does not cause detrimental effects on the enzyme activity of producing hydrogen. This can be explained by the high catalytic ability and the segregation layer from the atmosphere provided by the hydrogen it produces. Meanwhile, the electron sacrificial agent VitaminC also adds to the “protection layer” of the hydrogenase in our system.
Figure Standard Relationship between voltage data and concentration.Following the method above , we obtain the rate of hydrogen evolution: the tip of the first period is 7.061 mV at 500s. This corresponds to 2.179 (0.3086*7.061) umol/L at 500s. Thus the rate is 0.0126 (2.179/500*3mL*1000) umol/s, for 0.1g E. coli. In comparison with the rate from reference 1, 0.0086mol umol/s. This 46% increase in the efficiency shows that our system not only functions, but is also a big improvement compared with a artificial hydrogen production system reported before .
Fig 3. The first figures of each sample are snapped under green laser of 558 nm wavelength and mCherry-SpyTags emit red fluorescence. The second figures of each sample are snapped under bright field of fluorescence microscopy and we can clearly see a group of bacteria.. The third figures are merged by the first and second ones. All photos are taken by Zeiss Axio Imager Z2.
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