UC Riverside

Nature has the ability to mineralize and build intricate nanostructures of inorganic materials with a very high precision. Various bio-molecules can mineralize and control the morphology and composition of inorganic materials at ambient conditions. Inspired by nature, this work focuses on utilizing the M13 virus, a filamentous phage, 880 nm in length and 6 nm in diameter, for mineralizing copper sulfide and copper oxide semiconductor nanomaterials. The various coat proteins of the virus can easily be modified to express different peptides with specific affinity to various inorganic materials. A phage-display technique was utilized to identify a copper sulfide binding peptide expressed on the entire pVIII coat protein of the virus. This modified phage was used for synthesizing copper sulfide nanoparticles along the length of the template. To increase the yield and coverage of the mineralized material on the phage-templates, non-specific electrostatic interactions between a negatively charged phage (E3) and positively charged copper ions were utilized to synthesize copper sulfide at ambient conditions. The mineralized material coated the phage template and was identified to be cubic Cu_1.8S, a non-stoichiometric phase of the copper sulfide material system. The material showed strong optical absorption below 800 nm due to band-to-band transitions and localized surface plasmon resonance (LSPR) peaks in the infrared region. The LSPR peaks increased in absorption and the electrical resistance of the materials decreased with time indicating an increase in the number of free carriers in the material due to exposure at ambient conditions. The free carrier increase was attributed to a compositional change on the surface of the material. The synthesized Cu_1.8S was utilized to fabricate NH₃ gas sensors. These gas sensors showed a high response to NH₃ gas which may be attributed to the large surface-to-volume ratio of the viral-templated nanomaterials. Finally, utilizing the non-specific electrostatic interactions between the E3 phage and positively charged cations, copper oxide nanoparticles were also synthesized along the viral-template. These semiconductor materials were identified to be a mixture of CuO and Cu₂O with a direct optical band gap of 2.87 eV. These viral-templated semiconductor nanomaterials have potential applications for incorporation into future devices.