Mar 2, 2010
Lift-off process integrates viral nanopatterning
Nanostructured materials offer favourable properties compared with their bulk counterparts and are promising building blocks for next-generation electronic, photonic and energy-storage devices. Particular interest is directed towards biologically inspired methods for synthesizing ordered, monodisperse nanoparticles and nanowires, which involve peptides, proteins and viruses. These biomolecules possess attractive properties such as high aspect ratios and functional groups that can catalyze surface reactions and provide structural tunability. While such synthesis processes have been well established, the integration of biological nanomaterials into functional devices and architectures still remains a concern.
In a recent article published in the journal Nanotechnology, researchers at the University of Maryland (UMD), US, have presented a series of fabrication methodologies for the integration of tobacco mosaic virus (TMV)-structured nanomaterials into batch nanomanufacturing. The TMV is a high aspect ratio plant virus, which can be genetically modified with functional groups that form strong bonds with metal ions and various surfaces.
Previously, the scientists have used this technique to synthesize self-assembled, vertically aligned metallic nanowires. In their current work, patterned assembly of these structures is presented as a versatile alternative for wafer-level processing applications.
Bottom-up and top-down combination
The processes are based on robust and structurally stable TMV-templated materials. Selective patterning of metal-coated as well as uncoated viruses in any desired geometry can be achieved through the combination of bottom-up biological self-assembly and traditional top-down lithography using lift-off processes.
More specifically, photolithography with positive or negative resists is used to define patterns on wafer surfaces followed by self-assembly of the biomolecules. Removal of the remaining resist using solvents or pH-modified developer solutions results in highly ordered, well defined arrays of virus-structured materials.
The unique self-assembly properties of the TMV allow this process to be extended from planar to complex three-dimensional silicon and polymer micro-architectures for the synthesis of hierarchical structures comprising of micro- and nano-components.
Expanding the toolbox
Finally, the conformality provided by atomic layer deposition (ALD) is used to create core/shell metal/metal oxide heterostructures, thus expanding the toolbox of available chemistries that can be combined with the TMV template.
The techniques presented in this work outline a simple and alternative route for incorporating structural nanomaterials in functional devices. The team is currently working on a series of applications that use patterned assembly of the viral nanotemplates; these include microbatteries and micro-fuel cells with nanostructured electrodes and catalysts, sensor arrays with virus receptor layers as well as hierarchical structures for the fabrication of superhydrophobic and superhydrophilic surfaces.
About the author
This research was conducted at the MEMS Sensors and Actuators Laboratory (MSAL) at the University of Maryland (UMD) in direct collaboration with researchers at the University of Maryland Biotechnology Institute (UMBI). The research team consists of: Konstantinos Gerasopoulos, the lead graduate research assistant at MSAL who is developing biofabrication processes and integrating TMV nanostructures in energy-storage devices; Dr Matthew McCarthy, a postdoctoral associate previously at UMD and currently at MIT focusing on expanding aspects of the work for superhydrophobic biomimetic surfaces; Parag Banerjee, a graduate student at UMD with experience in ALD processes; Xiaozhu Fan, a graduate student at MSAL working on virus-based nanosensors; Dr James N Culver, professor and biologist at the Center for Biosystems Research at UMBI, whose interests lie in the use of biomaterials in nanotechnology applications. The principal investigator and co-ordinator of these activities is Dr Reza Ghodssi, professor of electrical engineering and director of MSAL and the Institute for Systems Research at the University of Maryland.