Fabrication of Water-Splitting Photoelectrode by Layer-by-Layer Assembly for Photobiocatalysis

Industrial application of biocatalysts have long been a dream of biochemists and bioengineers because of many advantages of biocatalysts over man-made catalysts. In principle, it is possible to synthesize virtually any kinds of chemicals with a high yield and selectivity by using enzymes under mild reaction conditions (e.g., aqueous solution, neutral pH, ambient temperature and pressure). To date, however, industrial application of biocatalysts has been very limited especially due to dependence of many enzymes on expensive cofactors. To solve such a problem, many efforts have been made to develop efficient way to recycle cofactors. Among a number of different methods, photochemical regeneration of cofactor has attracted numerous attention from researchers due to its environmental friendliness. For example, it has been reported that chiral model compounds such as L-glutamic acid can be continuously produced by glutamate dehydrogenase upon in situ regeneration of NAD(P)H cofactors with photosensitizers and electron mediators, the so-called biocatalytic artificial photosynthesis. Despite its huge potential, biocatalytic artificial photosynthesis is still at its infancy and far from true artificial photosynthesis because it still requires sacrificial electron donors for regeneration of cofactors. To address such a problem, in the present study we have developed a novel method to fabricate photoelectrodes, which can split water and produce electrons, provide them to electron mediators, and eventually enable regeneration of cofactors. We found that multiple components for photocatalytic water-splitting can be readily assembled on substrate by a simple layer-by-layer assembly technique and the prepared electrode shows water-splitting activity under visible irradiation. Based on these findings, we are currently trying to further integrate biocatalytic assemblies on the photoelectrode to take a step closer to realization of biocatalytic artificial photosynthesis