Our design is composed of three parts: biosynthesis of CdS semiconductor, light-driven nitrogen fixation and a light-driven biohybrid reaction device. This system is the expansion of our previous project of hydrogen production (Nanjing-China 2016), and it proves that surface display mechanism is capable of being expanded to a general principle for light-driven biohybrid reactions.

Biosynthesis of CdS semiconductor on cell surface

To construct our light-driven system, we induce the in situ synthesis of CdS semiconductor on the E. coli cell surface. One key element of our system is fused protein OmpA-PbrR. OmpA (Outer membrane protein A) fixes the protein complex on outer cell membrane while PbrR (lead-specific binding protein) adsorbs Cd2+ in the environment and further forms CdS semiconductor on cell surface.

After Cd2+ ions are added into the culture, the ions specifically bind to PbrR protein contributing to the aggregation of Cd2+. Combining with S2- ions in the media, CdS semiconductors are therefore formed on the outer membrane of cells.


Light-driven nitrogen fixation in E. coli cells

When the system is exposed in light, electrons of the CdS semiconductor conduct transit, and CdS provide these excited electrons to the electrons to Mo-Fe protein subunit of nitrogenase. Subsequently, the Mo-Fe protein utilizes the energy from these electrons to reduce N2(dinitrogen) to NH3(ammonia). Finally, the semiconductor regains its lost electron from sacrificial electron donors.

This design is of general applications as OmpA protein is merely a surface display mechanism for E. coli, and PbrR can be replaced with other proteins with different specificity.


Reaction device

We also designed a light-driven biohybrid reaction device to apply our system to practical use. After a few test, we proved our device to be quite practical. (see hardware for more details)