Two-dimensional (2-D) surface layer (S-layer) protein lattices isolated from the gram-positive bacterium Deinococcus radiodurans and the acidothermophilic archaeon Sulfolobus acidocaldarius were investigated and compared for their ability to biotemplate the formation of self-assembled, ordered arrays of inorganic nanoparticles (NPs). The NPs employed for these studies included citrate-capped gold NPs and various species of CdSe/ZnS core/shell quantum dots (QDs). The QD nanocrystals were functionalized with different types of thiol ligands (negative- or positive-charged/short- or long-chain length) in order to render them hydrophilic and thus water-soluble. Transmission electron microscopy, Fourier transform analyses, and pair correlation function calculations revealed that ordered nanostructured arrays with a range of spacings (approximately 7-22 nm) and different geometrical arrangements could be fabricated through the use of the two types of S-layers. These results demonstrate that it is possible to exploit the physicochemical/structural diversity of prokaryotic S-layer scaffolds to vary the morphological patterning of nanoscale metallic and semiconductor NP arrays.

Arrays of Au nanoparticles were created using the inherent repeating patterns of bacterial S-layer proteins. Bacterial self-assembling S-layer protein lattices display a highly repetitive surface structure that makes them particularly suitable as biotemplates to fabricate metallic/semiconducting nanostructures and arrays. One interesting S-layer for nanoparticle templating is the hexagonally packed intermediate (HPI) layer of Deinococcus radiodurans. This S-layer, displaying hexagonal (p6) symmetry, is comprised of a hexameric protein core unit with a central pore, surrounded by six relatively large openings (“vertex points”). In this work, the influences of particle properties and adsorption conditions on the formation of ordered arrays of 5-nm Au nanoparticles using HPI S-layers were investigated. Using transmission electron microscopy (TEM), it was found that the templating of citrate-capped Au nanoparticles on HPI layers under low ionic strength conditions resulted in hexagonal-packed ordered arrays with ∼18-nm interparticle spacings that corresponded with the pore-to-pore distance of the S-layer. Interestingly, nanoparticle binding occurs at the vertex points on the HPI layer and, due to repulsion forces, adsorption tends to be favored at every second vertex point. Upon increasing the ionic strength, ordered packing is still observed. However, because interparticle repulsions are less prominent, adsorption of nanoparticles occurs in virtually every available vertex point, resulting in the formation of a honeycomb-like pattern of nanoparticles extending throughout the HPI monolayer sheet. Combined with the results of additional investigations using either uncharged hydroxy-terminated particles or positively charged ferritin molecules, the experimental data suggest that the creation of ordered arrays through biotemplating of Au nanoparticles onto HPI S-layers depends on the electrostatic interactions between individual nanoparticles as well as the interaction with the HPI layer.

We investigated the formation of self-assembled two-dimensional (2-D) arrays of dendrimer-encapsulated platinum nanoparticles (Pt-DENs) using prokaryotic surface-layer (S-layer) proteins as biomacromolecular templates. The Pt-DENs (mean core diameter 1.8 +/- 0.5 nm) were synthesized by chemical reduction of metal ion species complexed within the interior of fourth-generation, hydroxyl-terminated, starburst poly(amidoamine) dendrimers (G4 PAMAM-OH). Detailed structural and elemental composition analyses performed using high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy indicated that the dendrimer-metal nanocomposite particles were crystalline in nature rather than amorphous and that at least some quantity of the platinum found within the particles is present in the expected zerovalent state. By using the S-layer lattices from the acidothermophilic archaeon Sulfolobus acidocaldarius and the Gram-positive bacterium Deinococcus radiodurans as a biotemplate, hexagonal- and honeycomb-ordered arrays of the Pt-DENs were successfully fabricated under a range of different pH conditions via noncovalent nanoparticle-protein interactions. Fast Fourier transform analyses of transmission electron microscopy images verified that the fabricated Pt-DEN assemblies displayed mean periodicities that corresponded well with the lattice constants of the native protein templates (i.e., 22 and 18 nm for S. acidocaldarius and D. radiodurans S layers, respectively). Our results demonstrate that utilizing pre-synthesized Pt-DENs in conjunction with microbial S-layer proteins displaying highly periodic topochemical properties can be an effective, novel route for creating patterned arrays of Pt nanoparticles with potential technological applications.

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We have fabricated high sheet density (>1011 cm−2) InAs quantum dots (QDs) on an InAlAs buffer layer composed of As-pressure-modulated (As-rich and As-lacking) InAlAs multilayer structure (AM–InAlAs–MLS) lattice matched to InP substrate. The AM–InAlAs–MLS buffer layer has greater advantages than the conventional InAlAs buffer layer in the formation of InAs QDs, because InAs quantum wires (QWRs) are easy to obtain instead of quantum dots on InAlAs. In addition, strong radiative efficiency at room temperature (RT) can be achieved from QDs on AM–InAlAs–MLS. These results indicate that the AM–InAlAs–MLS can suppress the QWR formation and result in QD growth with high density and strong RT radiative efficiency, which is helpful for further understanding the mechanism of morphology control on the QDs.