Bacterial surface-layer proteins for electrochemical nanofabrication

Microorganism-mediated synthesis of chemically difficult-to-synthesize Au nanohorns with excellent optical properties in the presence of hexadecyltrimethylammonium chloride

Closely packed, size-controllable and stable Au nanohorns (AuNHs) that are difficult to synthesize through pure chemical reduction are facilely synthesized using a microorganism-mediated method in the presence of hexadecyltrimethylammonium chloride (CTAC). The results showed that the size of the as-synthesized AuNHs could be tuned by adjusting the dosage of the Pichia pastoris cells (PPCs). The initial concentrations of CTAC, ascorbic acid (AA) and tetrachloroaurate trihydrate (HAuCl4·3H2O) significantly affected the formation of the AuNHs. Increasing the diameters of AuNHs led to a red shift of the absorbance bands around 700 nm in their UV-vis-NIR spectra. Interestingly, the AuNH/PPC composites exhibited excellent Raman enhancement such that rhodamine 6G with concentration as low as (10(-9) M) could be effectively detected. The formation process of the AuNHs involved the initial binding of the Au ions onto the PPCs with subsequent reduction by AA to form supported Au nanoparticles (AuNPs) based on preferential nucleation and initial anisotropic growth on the platform of the PPCs. The anisotropic growth of these AuNPs, which was influenced by CTAC and PPCs, resulted in the formation of growing AuNHs, while the secondary nucleation beyond the PPCs produced small AuNPs that were subsequently consumed through Ostwald ripening during the aging of the AuNHs. This work exemplifies the fabrication of novel gold nanostructures and stable bio-Au nanocomposites with excellent optical properties by combining microorganisms and a surfactant.

Three-dimensional architecture of inorganic nanoarrays electrodeposited through a surface-layer protein mask

Transmission electron microscopy was used to analyze the three-dimensional (3D) architecture of cuprous oxide electrochemically deposited through the pores of the hexagonally packed intermediate surface-layer protein from Deinococcus radiodurans SARK. Imaging at multiple tilt angles and averaging from five different samples allowed approximately 3 nm computed 3D reconstructions of the inorganic deposit and protein template. We show that the electrodeposition process used here was able to fully access the pore structure that penetrates the protein layer, allowing the fabrication of a polycrystalline nanoarray with 18 nm periodicity and lateral interconnectivity among the pores with 3-fold symmetry. At the resolution of the reconstruction, the 6-fold symmetry pores also appear filled but are not connected laterally to the rest of the deposit. These results show that electrochemical deposition can produce interconnected 3D structures at dimensions an order of magnitude smaller than the most advanced integrated circuits (IC), boding well for continued down-scaling of electrodeposition to meet the needs for future generations of IC device interconnects.