Biological semiconductors: self-assembled shell proteins as photoactive materials.

Area of Science:

• Biomaterials Science
• Bioelectronics
• Protein Engineering

Background:

• Light-harvesting proteins are attractive for bioelectronics but suffer from instability and poor charge transport.
• External scaffolds can improve stability but lead to energy losses and slower response times.

Purpose of the Study:

• To identify and characterize novel, stable, and efficient photoactive materials for bioelectronic applications.
• To explore the potential of bacterial shell proteins as self-assembling, scaffold-free components in bioelectronics.

Main Methods:

• Identification and characterization of hyper-thermostable, self-assembling bacterial shell proteins.
• Structural analysis of disc-like protein assemblies with organized tyrosine residues.
• Electrical characterization using current-voltage (I-V) profiling and ultraviolet photoelectron spectroscopy (UPS).
• Photocurrent generation measurements under UV illumination and mutational analysis to elucidate electron transfer mechanisms.

Main Results:

• Bacterial shell proteins form stable, disc-like structures with spatially organized tyrosine residues.
• These protein discs exhibit semiconducting behavior with a low work function (<3 eV).
• Photocurrent generation was observed under UV illumination without external bias, with external quantum efficiencies of ~0.5% and response times of 0.3 s.
• A tyrosine-mediated electron transfer mechanism was implicated through mutational studies.

Conclusions:

• Bacterial shell proteins are intrinsically stable, self-assembling, and scaffold-free photoactive materials.
• These proteins offer significant advantages over traditional photosynthetic proteins for bioelectronic applications.
• The findings pave the way for next-generation bioelectronic devices utilizing engineered protein materials.