A five-and-a-half-year integrated multidisciplinary research project has been characterized by three themes pertinent to the development of advanced materials having tailorable microstructures and/or nanostructures. These themes are (1) biocompatible nanolithographic methods of patterning and templating of materials to have two- and three-dimensional nanostructures; (2) nucleic-acid-based approaches to preparing (both in solution and from predesigned, nanostructured surface templates) supramolecular structures tailored to perform specific functions; and (3) protein-based or inspired molecular and supramolecular architectures. The contributions of this and other related research projects can be expected to lead to the development of diverse nanostructured organic and inorganic materials and structures, including catalytic peptide tubes, hostguest materials for molecular separations, quantum-dot and magnetic-particle arrays, bio-nanoelectronic circuitry, photonicbandgap and three-dimensional electronic power structures, and novel biowarfare- detection materials.

From one perspective, the objectives of this research project have been the following:

  • To establish the basic chemical and physical rules that govern the use of such biomolecules as those of deoxyribonucleic acid (DNA), ribonucleic acid (RNA), peptide nucleic acid (PNA), peptides, and proteins for the assembly of two- and three-dimensional organic and inorganic structures having predictable and useful properties;
  • To merge solution-phase strategies for assembly of three-dimensional nanostructures with surface-directed strategies that involve reliance on dip pen nanolithography (DPN); and
  • To develop computational means of predicting the structural, optical, electrical, and mechanical properties of novel templated structures synthesized according to the abovementioned concepts.
A Nanofiber can be made by self-assembly of peptide amphiphile molecules that have been suspended in an acidic solution. Modification of the peptide sequence in the molecules changes the nature of fiber-surface molecular-recognition sites.

Progress toward these objectives is manifested in the findings and accomplishments of several different sub-projects into which the research project was divided. Each sub-project emphasizes, and is named for, one aspect of the overall subject matter. The names of the subprojects and their respective efforts, accomplishments, and/or findings are summarized as follows:

  • Supramolecular Assembly Using Bio-Inspired Approaches

    One group of researchers involved in this sub-project focused primarily on exploiting the structural features of selfassembling cyclic D, L-a-peptide nanotubes in the context of self-organizing organic conductors and semiconductors and secondarily on rational design of self-assembling peptide nanotubes carrying different structural and functional features suitable for the fabrication of new biologically active materials. Other groups involved in this sub-project addressed diverse topics, including collagen- like peptides and their threedimensional structures, polymer amphiphiles and formation of micelles, metal organic-based biomolecule nanoarrays, self-assembly of peptide amphiphile nanofibers (see figure), alignment of supramolecular structures based on peptide amphiphiles, a selfassembly system based on peptide lipid hybrid molecules, and synthesis of composite nanorods and assembly thereof into three-dimensional superstructures.

  • DPN and its Applications

    Whittling by means of electrochemical desorption was developed as a means of reducing the sizes of DPNgenerated nanostructures on gold surfaces. Enzymatic polymerization was used in conjunction with DPN patterning of reactive monomers of 4-amin - othiophenol and caffeic acid to synthesize conducting polymers. Protocols for the assembly of nanoarrays composed of functional antibodies for the detection of the p24 protein of the human immunodeficiency virus 1 (HIV-1) were developed. A novel, high-throughput, high-resolution DPN technique called “on-wire lithography” (OWL) was developed for the lithographic processing of metallic nanowires having dents or gaps ranging in size from five to several hundred nanometers. These structures are ideal candidates to be developed into nanoelectronic and molecular electronic devices.

  • Functional Materials for Data

    Storage, Sensing, and Diagnostics DPN-derived templates were used for the assembly of inorganic colloidal structures. It was found that both magnetic and dielectric colloids could be directly assembled or patterned onto the templates. It was found that sol-gels could be used as inks and patterned onto noble-metal and oxide substrates and that through the choice of sol-gel precursors, tailored ceramic materials could be formed. The sol-gel-precursor approach is expected to open new avenues for fabricating nanostructures capable of functioning as sensory, data-storage, and mag - neto/electronic devices. Other accomplishments of this sub-project include development of techniques for fabrication of nanoelectrodes, biosensory devices, and electrically conductive polymer nanostructures; development of a method of multiplexed localized patterning of polymers; and fabrication and determination of electrical properties of gold nanoparticles coated with organic material.

  • Computational Modeling of Self- Assembly

    Computational models of physical and chemical phenomena involved in self-assembly of nanostructures were developed. The models were utilized in computational-simulation studies in which significant progress was made towards understanding, on a theoretical and experimental level, how two types of model molecules — alkyl thiols and peptide amphiphiles — assemble themselves on surfaces. Effects of environmental factors on the shapes and properties of structures formed by such selfassembly were analyzed.

This work was done by Chad A. Mirkin, Vinayak Dravid, Mark Ratner, George Schatz, Sam Stupp, David Kaplan, Reza Ghadiri, and David Ginger of Northwestern University for the Air Force Office of Scientific Research.

This Brief includes a Technical Support Package (TSP).
Progress in Design and Synthesis of Nanostructured Materials

(reference AFRL-0089) is currently available for download from the TSP library.

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