University Of Maryland Biotechnology Institute
(Baltimore, MD) and Purdue Research Foundation
(West Lafayette, IN) scientists have developed metal coated virus-based nanoelectrodes and methods of assembling the electrodes with a modified tobacco virus. The nano-scaffolds, and more specifically, genetically engineered nanoscale metal reactive surfaces are useful in nano-devices, including sensors, solar cells, batteries, electrodes, transistors, semiconductor chips and capacitors, according to U.S. Patent Application 20100093562
.According to inventors James N. Culver (Potomac, MD), Michael Harris (Lafayette, IN) and Elizabeth Royston; (Columbia, MD), the electrodes have high content surface areas containing nickel and/or cobalt metallic compounds assembled on a modified Tobacco mosaic virus (TMV) template. The modified TMV template is engineered to encode unique placement of cysteine residues that self-assemble onto gold patterned surfaces in a substantially aligned fashion, producing a >10 fold increase in surface area. Deposition of ionic metals onto the surface assembled virus templates produce uniform metal coatings for the fabrication of oriented high surface area materials.
High surface area nanostructured materials have uses in an array of applications including electrodes, catalyst supports, thermal barriers, sensor arrays and energy storage devices. Increased surface areas are generally achieved through the synthesis of particles with high surface to volume ratios or the manufacture of nanostructured materials from bulk substrates. Methods used to create high surface area nanostructures, such as laser ionization or lithography, generally require complex and expensive technologies that can limit the application of these materials.
To avoid such limitations, researchers are increasingly investigating alternative methods for the self-assembly of high surface area nanostructured materials and devices. One approach is templating materials onto biologically derived substrates. Biological templates such as nucleic acids and viruses have evolved to self-assemble into hierarchically ordered structures with high surface to volume aspects, making them ideal for the synthesis of high surface area nanomaterials.
The genetically engineered TMV virus provides for active sites to interact and adhere to a metal surface and also provide a template for deposition of conductive metal clusters.
The virus cages may be loaded with inorganic materials, including, but not limited to, metals, metal salts, metal oxides (including neat, doped and alloyed metal oxides), non-metal oxides, metal and non-metal chalcogens, sulfides, selinides, coordination compounds, organometallic species. Preferably, suitable metals include, but are not limited to, monovalent and polyvalent metals in any form depending on the end use of the nanostructure, including, but limited to aluminum, barium, cadmium, chromium, cobalt, copper, europium, gadolinium, lanthanum, magnesium, manganese, nickel, platinum, neodymium, titanium, yttrium, zirconium, terbium, lithium, zinc and iron, as well as other lanthanides. Metals that can possess magnetic properties may also be used.
FIG. 1 shows the steps for the assembly of nickel or cobalt-coated TMV1cys templates and attachment to a gold surface. TMV was genetically engineered to express a novel coat protein cysteine residue, TMV1cys, which was then used to vertically pattern TMV particles onto gold surfaces via gold-thiol interactions. Importantly, it was found that the TMV1cys readily bound to gold surfaces and remained attached during mineralization while the unmodified wild-type virus did not (data not shown). Then an electroless deposition strategy was used to show that surface assembled TMV1cys are mineralized in a uniform manner.
Notably, patterned TMV virion particles, with one or more added cysteine residues, function as robust templates for the reductive deposition of nickel and cobalt at room temperature via electroless deposition, producing dense carpets of oriented metal-coated viral templates. Mineralized surface assembled viruses significantly increased available surface area and enhanced electrode life and voltage output in a battery electrode system. The controlled self-assembly of these virus templates in an oriented manner combined with their enhanced functionalization to produce uniform high surface area electrodes represents a significant advance toward the manufacturing of biologically based devices.
FIG. 2 shows FESEM images showing (a) a nickel-coated gold surface without TMV1cys, (b) a cobalt coated gold surface without TMV1cys, (c) a nickel-coated gold surface with 1 mg/mL TMV1cys, (d) a cobalt-coated gold surface with 1 mg/mL TMV1cys.
FIG. 3 shows a TEM image showing a 70 nm thick cross section of nickel-coated TMV1cys attached perpendicular to a gold-coated mica surface. Coating thicknesses of nickel encasing each particle were measured at .about.20 nm. Scale bar is equal to 300 nm.
FIG. 4 shows a computer generated model diagramming the position of the 1cys mutations relative to the (a) outer rod surface and (b) the 3′ end.
The biologically derived components are unique in that they can encode novel specificities as well as the ability to self-assemble into defined structures. Thus, they have tremendous potential for use in the development and application of a variety of nanoscale devices. One of the challenges in the use of biological components is the ability to integrate these components into devices in a functionally useful way.
The integration of TMV1cys based nanotemplates onto a solid surface was accomplished to produce functional high surface area nanomaterials. This self-assembly process works at room temperature and under mild buffer conditions and produces nanostructured materials that are uniformly oriented and coated. The density of surface assembled virus and thus available surface area are easily tuned by varying the virus concentration of the assembly reaction. A simple electroless deposition method allows the efficient and uniform metal coating of assembled virus. Once coated, surface attached viruses were highly stable under a variety of conditions including repeated washings with acetone and vacuum drying.