Technical: Self-assembled molecular circuits hold the promise of dramatic reductions in manufacturing and energy costs compared to conventional lithographic techniques, as well as the possibility of completely new functionalities. Creation of complex self-assembled circuits requires an easily programmable and sophisticated recognition capability; this can be provided by DNA. For electronic devices, the DNA must conduct charge. However, for distances longer than 50 nm, the conductivity of DNA is poor, especially in the dry state. In this work, methods for increasing the conductivity of DNA will be explored and characterized. The specific objectives of this work are: (1) Investigate methods of imparting long-range conductivity or photoconductivity to DNA by forming DNA/chromophore hybrids of two types, one with porphyrins intercalated into the base stack and one using modified bases that absorb in the near UV. (2) Refine techniques for selectively attaching the DNA/chromophore hybrids to specific electrodes, a requirement for the development of complex circuits. (3) Test predictions of a model for the photoelectronic properties of porphyrin-containing self-assembled nanowires, using 4-probe measurements, measurements under ultrahigh vacuum and variable O2 concentration, and measurements using circularly-polarized light. (4) Develop methods of creating three-terminal junctions in the DNA-chromophore hybrids, and also test for cross-talk between crossing hybrid strands. The work also focuses on nanowires self-assembled solely from porphryin molecules. These may have applications in molecular electronics, including light harvesting. Furthermore, probing the porphryin nanowires can give important insights about fundamental mechanisms in the DNA/chromophore hybrids.
The results of this work will help to lay the foundations for an eventual true revolution in self-assembled molecular electronics. This field is at the stage where a deeper understanding of the basic science is needed to make progress. This work will provide pioneering insights into the physics of conductivity (as opposed to transfer of single charges) in DNA-chromophore hybrids. This research will include the first measurements of the effects of circularly polarized light on the photoelectronic properties of a self-assembled nanofilament. Results from this work will motivate researchers in physics, physical chemistry, and biophysics. Fifteen undergraduates and three high-school students will get an intense, cutting-edge research experience, including training in careful scientific practice as well as subfield-specific training. About 40% of these will be from groups underrepresented in physics (women, African-Americans, and Latinos). Each student will create a web page including a video interview to present his/her research to the general public. The PI will use his experience from mentoring 79 undergraduate research students to create a website/wiki devoted to mentoring physics undergraduate researchers, with sections devoted to each subdiscipline of physics. The PI will host the condensed matter portion of the website, will recruit other faculty to host the other sections, and will publicize the site by methods including annual contacts with all coordinators of physics 'Research Experience for Undergraduates' programs. This website will be consulted by many research mentors each year, and will provide at least a 10% improvement in the research efficiency of their students, corresponding to thousands of work hours for all the students put together in a single year. Further, the habits instilled in these students should persist through graduate school and beyond.
