Polypeptide supramolecules that will self assemble from solution and will form molecular wires that exploit quantum mechanical transport mechanisms can enable the formation of molecular devices such as transistors, diodes, and sensors. The peptides were designed and then arranged on substrates using self-assembly, Dip-PEN nanolithography, and e-beam assisted lithography. The peptides were characterized using atomic force microscopy (AFM) and the electrical properties of the self-assembled interconnects are characterized as well. These peptides can be nanoengineered/nanoassembled individual building blocks at the molecular level to form conducting channels towards realization of molecular MOSFETs/CMOS device technology.

Electrical measurements of Synthesized Polypeptides were carried out using a scanning tunneling microscope. Peptides were synthesized in between two terminal electrodes made of nickel.
Polypeptides were engineered to contain specific amino acid sequences, chain lengths, and conformation with an extremely high degree of monodispersity. The polypeptide polymers with repetitive AlaGly (Alanine, Glycine) sequences were designed and subsequently synthesized via over expression by E.Coli. Molecular biological techniques permit peptide engineering via the replacement of naturally occurring amino acids with synthetic analogues by relaxing the specificity of the aminyl-tRNA synthetase. Such a methodology was developed for the monodisperse synthesis of functionalized polypeptides for surface-directed assembly.

The polypeptide is composed of an amino acid chain comprised of Alanine, Glycine, Phenylalanine (Phe), and Cysteine (Cys). The attachment to poly peptide via polyhistidine side groups was carried out, as it gives a very good ohmic contact with metals such as nickel, which was selected as the electrode surface to allow covalent attachment of the polypeptide functional end moieties.

A series of polypeptides at different concentrations was prepared. The peptides have 256 repeats, which correspond to channel length of about 3-5 microns). Atomic force microscopy surface topography measurements of self-assembled polypeptide nanostructures was carried out using BioScope II to document the surface roughness, determine polypeptide domain structure, and evaluate lamellae assembly.

Electrical measurements of synthesized polypeptides were carried out using scanning tunneling microscopy. Peptides were synthesized in between two terminal electrodes made of nickel. The polypeptide-based molecular quantum crystal wires are a candidate building block of synthesized peptides between the two-terminal device and direction of current flow. One end of the electrode was grounded and an STM conducting probe was placed on the other end of the electrode.

The molecular interconnects will be able to form part of the building blocks for portable devices. The peptides can be designed to have specific affinity to the substrate and can contain moieties that can be organized to serve as conducting channels. Self-assembled peptides have shown conducting characteristics. Both soft e-beam lithography and DIP-PEN method are also suitable for patterning for polypeptides.

This work was done by Yeng Ming Lam, Mhaisalkar Subodh, and Lain-Jong Li of Nanyang Technological University, Singapore; Vinayak P. Dravid and Dr. Gajendra S. Shekhawat of Northwestern University; and Dr. C. Raman Suri of the Institute of Microbial Technology, India. AFRL-0119

This Brief includes a Technical Support Package (TSP).
Polypeptide-Based Molecular Electronics

(reference AFRL-0119) is currently available for download from the TSP library.

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