Electrochemical nanofabrication using crystalline protein masks

0,1,2,3D nanostructures, types of bulk nanostructured materials, and drug nanocrystals: An overview

Functional materials are required to meet the needs of society, such as environmental protection, energy storage and conversion, integrated product production, biological and medical processing. bulk nanostructured materials are a research concept that combines nanotechnology with other research fields such as supramolecular chemistry, materials science, and life science to develop logically functional materials from nanodevices. In this review article, nanostructures are synthetized by different methods based on the types and nature of the nanomaterials. In a broad sense "top-down" and "bottom-up" are the two foremost methods to synthesize nanomaterials. In top-down method bulk materials have been reduced to nanomaterials, and in case of bottom-up method, the nanomaterials are synthesized from elementary level. The different methods which are being used to synthesize nanomaterials are chemical vapor deposition method, thermal decomposition, hydrothermal synthesis, solvothermal method, pulsed laser ablation, templating method, combustion method, microwave synthesis, gas phase method, and conventional Sol-Gel method. We also briefly discuss the various physical and chemical methods for producing nanomaterials. We then discuss the applications of functional materials in many areas such as energy storage, supercapacitors, sensors, wastewater treatment, and other biological applications such as drug delivery and drug nanocrystals. Finally, future challenges in materials nanoarchitecture and concepts for further development of functional nanomaterials are briefly discussed.

Automated Combinatorial Process for Nanofabrication of Structures Using Bioderivatized Nanoparticles

A fully automated electronic microarray control system (Nanochip 400 System) was used to carry out a combinatorial process to determine optimal conditions for fabricating higher order three-dimensional nanoparticle structures. Structures with up to 40 layers of bioderivatized nanoparticles were fabricated on a 400-test site CMOS microarray using the automated Nanochip 400 System. Reconfigurable electric fields produced on the surface of the CMOS microarray device actively transport, concentrate, and promote binding of 40 nm biotin- and streptavidin-derivatized nanoparticles to selected test sites on the microarray surface. The overall fabrication process including nanoparticle reagent delivery to the microarray device, electronic control of the CMOS microarray and the optical/fluorescent detection, and monitoring of nanoparticle layering are entirely controlled by the Nanochip 400 System. The automated nanoparticle layering process takes about 2 minutes per layer, with 10–20 seconds required for the electronic addressing and binding of nanoparticles, and roughly 60 seconds for washing. The addressing and building process is monitored by changes in fluorescence intensity as each nanoparticle layer is deposited. The final multilayered 3D structures are about 2 μm in thickness and 55 μm in diameter. Multilayer nanoparticle structures and control sites on the microarray were verified by SEM analysis.

Nanoscale patterning of a self-assembled monolayer by modification of the molecule-substrate bond

The intercalation of Cu at the interface of a self-assembled monolayer (SAM) and a Au(111)/mica substrate by underpotential deposition (UPD) is studied as a means of high resolution patterning. A SAM of 2-(4'-methylbiphenyl-4-yl)ethanethiol (BP2) prepared in a structural phase that renders the Au substrate completely passive against Cu-UPD, is patterned by modification with the tip of a scanning tunneling microscope. The tip-induced defects act as nucleation sites for Cu-UPD. The lateral diffusion of the metal at the SAM-substrate interface and, thus, the pattern dimensions are controlled by the deposition time. Patterning down to the sub-20 nm range is demonstrated. The difference in strength between the S-Au and S-Cu bond is harnessed to develop the latent Cu-UPD image into a patterned binary SAM. Demonstrated by the exchange of BP2 by adamantanethiol (AdSH) this is accomplished by a sequence of reductive desorption of BP2 in Cu free areas followed by adsorption of AdSH. The appearance of Au adatom islands upon the thiol exchange suggests that the interfacial structures of BP2 and AdSH SAMs are different.

Self-assembled two-dimensional protein arrays in bionanotechnology: from S-layers to designed lattices

Although the crystalline S-layer arrays that form the exoskeleton of many archaea and bacteria have been studied for decades, a long-awaited crystal structure coupled with a growing understanding of the S-layer assembly process are injecting new excitement in the field. The trend is amplified by computational strategies that allow for in silico design of protein building blocks capable of self-assembling into 2D lattices and other prescribed quaternary structures. We review these and other recent developments toward achieving unparalleled control over the geometry, chemistry and function of protein-based 2D objects from the nanoscale to the mesoscale.

Silver nanotubes — Biopolymer-assisted hydrothermal synthesis

In this paper, we further the biopolymer-assisted hydrothermal approach to synthesize silver nanotubes with an outer diameter of 200–300 nm, a tube wall around 50 nm, and a length of several micrometers. Here, the biopolymer is a hyaluronic acid potassium salt (HAPS). This result further verified the validity of this green biopolymer-assisted hydrothermal route for the fabrication of nanomaterials. It also gives some proof that HAPS can provide an anisotropic growth environment, which favors the formation of silver nanotubes with a nonlayered structure. The formation mechanism has been tentatively explained based on Ostwald ripening and the capping action of HAPS. In the long run, the obtained silver nanotubes can be used as a chemical template to fabricate alloyed nanotubes through the galvanic replacement reaction.

Biotemplating of metallic nanoparticle arrays through site-specific electrostatic adsorption on streptavidin crystals

The protein streptavidin exhibits unique properties advantageous for "bottom-up" nanofabrication applications. It self-assembles into various 2-D crystalline lattices onto which nanoparticles can be attached through both electrostatic and ligand-receptor mechanisms. We examine the electrostatic adsorption of gold nanoparticles onto non-close-packed streptavidin crystals and show that site-specific attachment preferentially occurs in between protein molecules. The resulting nanoparticle arrangement consequently displays a long-range structural coherence with the underlying protein lattice, although with a reduced degree of order relative to that of the biological template. Monte Carlo simulations reveal that this remittent ordering is due to (1) the random offset between the nanoparticles and their respective adsorption sites and (2) nonspecific binding to the surface of the protein molecules. Overall, our results indicate that streptavidin crystals are capable of templating ordered nanoparticle arrays.

Fabrication and electrochemical characterization of TiO2 three-dimensional nanonetwork based on peptide assembly

The three-dimensional network of TiO(2) hollow nanoribbons designed from a peptide assembly using atomic layer deposition is demonstrated as a promising Li secondary battery electrode in this study. The nanoribbon network ensures effective transport of electrons and Li ions due to (i) a well-connected network of nanoribbons and (ii) the hollow structure of each nanoribbon itself, into which Li ions in the electrolyte can readily diffuse. The improved specific capacity, rate capability, and cyclability of the nanonetwork show that the utilization of a nanonetwork of individual hollow ribbons can serve as a promising strategy toward the development of high-performance electrode for Li secondary batteries.

Electrodeposition of metal wires onto a molecular scale template: an in situ investigation

We have demonstrated that the intrinsic nanometer length scales of two-dimensional molecular assemblies can be exploited to electrodeposit metal nanostructures with regular spacing and orientation. We observed evidence for preferential deposition of metals into parallel lines on Au(111) surface with a periodicity of 4.5 nm as determined by the hemimicelles formed by sodium dodecylsulfate. The preferential deposition of metals in molecular templates was achieved under optimal electrode potentials and ionic concentrations. The observed metal structures provide insight into the interactions between metal atoms, organic functional groups as well as the aqueous environment. Understanding and tailoring these interactions will lead to more precise control and new strategies for nanoscale placement and for connecting organic molecules to metal nanostructures.

Directed hybridization of DNA derivatized nanoparticles into higher order structures

Electric field directed hybridization was used to produce twenty layer nanostructures composed of DNA derivatized nanoparticles. Using an electronic microarray device, DNA nanoparticles could be directed and concentrated such that rapid and specific hybridization occurs only on the activated sites. Nanoparticle layers were formed within 30 s of activation and twenty layer structures completed in under an hour. Results demonstrate a unique combination of bottom-up and top-down techniques for nanofabrication.

Surface-templated formation of protein microfibril arrays

Ordered arrays of collagen microfibrils form rapidly and spontaneously from a solution of monomers deposited onto a mica substrate. These arrays are well-ordered and apparently continuous over the entire substrate. Correlated atomic force microscope images and Laué diffraction patterns indicate that the protein alignment and microfibril formation is controlled by the crystal orientation of the mica substrate rather than fluid flow or drying effects. This surface-induced mechanism allows for immediate, robust, and reproducible pattern formation.

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.

Electric-field-directed assembly of biomolecular-derivatized nanoparticles into higher-order structures

Multilayered structures composed of biomolecule-derivatized nanoparticles can be fabricated by electric-field-directed self-assembly. A microelectrode-array device facilitates the rapid parallel electrophoretic transport and binding of biotin and streptavidin fluorescent nanoparticles to specific sites on the microarray. Control of the current, voltage, and activation time of each of the 400-microarray electrodes allows a combinatorial approach to optimize nanoparticle binding. Under optimal conditions, nanoparticle layers form within 15 s of microelectrode activation, and the directed assembly of more than 50 alternate layers of nanoparticles is complete within an hour. The final multilayered structures are removed from the support by a relatively simple lift-off process. The electric-field process allows the parallel patterned assembly of multilayer structures using extremely low concentrations of nanoparticles and produces minimal nonspecific binding to unactivated sites. These results are significant for the development of rapid, maskless nanofabrication and hierarchical integration of biomolecular-derivatized nanocomponents into higher-order materials and devices.

Stability of S-layer proteins for electrochemical nanofabrication

Crystalline cell surface layer proteins (S-layers) can be used in electrochemical fabrication to create nanoscale arrays of metals and oxides on surfaces so long as the proteins maintain their long-range order during processing. We have explored the stability of the HPI layer protein (the S-layer protein from the microorganism Deinococcus radiodurans) adsorbed onto platinum surfaces after immersion in sulfuric acid or sodium hydroxide electrolytes ranging in pH from 0 to 14 over time periods ranging from 1 to 1000s. Topographic data obtained by atomic force microscopy (AFM) was used to characterize the protein stability, judged by its retention of long-range order after immersion. The compiled data revealed that, under these solution conditions and in this environment, the HPI layer protein has a dose-dependent structural stability "envelope" in the acidic range from 1<pH<4. The protein retains its long-range order up to 1000s from pH 4 to 11, and has a sharp stability edge between pH 12 and 13. Interestingly, the more stringent requirement of stability (i.e., retention of long-range order) defined in the context of electrochemical fabrication for this protein narrowed the window of stability in pH and time when compared to previous stability studies reported for this protein.

Bionanofabrication of metallic and semiconductor nanoparticle arrays using S-layer protein lattices with different lateral spacings and geometries

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.

Nanoscale Patterning of Two Metals on Silicon Surfaces Using an ABC Triblock Copolymer Template

Patterning technologically important semiconductor interfaces with nanoscale metal films is important for applications such as metallic interconnects and sensing applications. Self-assembling block copolymer templates are utilized to pattern an aqueous metal reduction reaction, galvanic displacement, on silicon surfaces. Utilization of a triblock copolymer monolayer film, polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) (PS-b-P2VP-b-PEO), with two blocks capable of selective transport of different metal complexes to the surface (PEO and P2VP), allows for chemical discrimination and nanoscale patterning. Different regions of the self-assembled structure discriminate between metal complexes at the silicon surface, at which time they undergo the spontaneous reaction at the interface. Gold deposition from gold(III) compounds such as HAuCl4(aq) in the presence of hydrofluoric acid mirrors the parent block copolymer core structure, whereas silver deposition from Ag(I) salts such as AgNO3(aq) does the opposite, localizing exclusively under the corona. By carrying out gold deposition first and silver second, sub-100-nm gold features surrounded by silver films can be produced. The chemical selectivity was extended to other metals, including copper, palladium, and platinum. The interfaces were characterized by a variety of methods, including scanning electron microscopy, scanning Auger microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy.

Block Copolymer-Templated Chemistry on Si, Ge, InP, and GaAs Surfaces

Patterning of semiconductor surfaces is an area of intense interest, not only for technological applications, such as molecular electronics, sensing, cellular recognition, and others, but also for fundamental understanding of surface reactivity, general control over surface properties, and development of new surface reactivity. In this communication, we describe the use of self-assembling block copolymers to direct semiconductor surface chemistry in a spatially defined manner, on the nanoscale. The proof-of-principle class of reactions evaluated here is galvanic displacement, in which a metal ion, M+, is reduced to M0 by the semiconductor, including Si, Ge, InP, and GaAs. The block copolymer chosen has a polypyridine block which binds to the metal ions and brings them into close proximity with the surface, at which point they undergo reaction; the pattern of resulting surface chemistry, therefore, mirrors the nanoscale structure of the parent block copolymer. This chemistry has the added advantage of forming metal nanostructures that result in an alloy or intermetallic at the interface, leading to strongly bound metal nanoparticles that may have interesting electronic properties. This approach has been shown to be very general, functioning on a variety of semiconductor substrates for both silver and gold deposition, and is being extended to organic and inorganic reactions on a variety of conducting, semiconducting, and insulating substrates.