Strands of DNA have been used as tiny scaffolds to create superconducting nanodevices that demonstrate a new quantum interference phenomenon. These nanowire quantum interference devices (NQIDs), which comprise a pair of suspended superconducting wires as thin as a few molecular diameters (5 nm to 20 nm), could be used to measure magnetic fields and to map out the phase of the order parameter in regions of superconductivity. The figure at the right shows an artist's conception of the NQID. Two strands of DNA have been suspended over a trench cut into a substrate and then sputtered with a superconducting alloy to create the nanowires and leads. Such novel metallic nanodevices can be integrated into large arrays using well-known self- assembly properties of DNA molecules. Novel quantum interference device made of DNA-templated superconducting nanowires Alexey Bezryadin, University of Illinois at Urbana-Champaign, DMR Reference: D. Hopkins et al., Science 308,1762 (2005)

Novel quantum interference device made of DNA-templated superconducting nanowires Alexey Bezryadin, University of Illinois at Urbana-Champaign, DMR If a single linear molecule (e.g. DNA) is decorated with a thin metallic film, an ultrathin wire obtains. Using this method a new type of device that is sensitive to local variations of the magnetic field have been produced. The fabrication goes as follows. First, two molecules of DNA are placed across a deep trench etched into a silicon substrate. The molecules appear straight because the molecule-surface attraction pulls on them. Subsequently the molecules and the areas on the two banks of the trench are covered with a very thin metallic film. The metal used is a superconducting alloy of Molybdenum (Mo) and Germanium (Ge). Superconducting means that it can carry current without any resistance. The metal is deposited sputtering, which is a physical method that provides good sticking of the deposited metal atoms to the suspended DNA molecules and the entire substrate. Finally each molecule becomes covered with a few atomic layers of the mixture of Mo and Ge. Thus each molecule transforms into a metallic nanowire with the DNA at its core, as shown in the drawing. Since the diameter of the DNA is ~ 2 nm, the resulting wires are about 5 to 20 nanometers in diameter, which is about 2,000,000 times thinner than one inch. Such thin wires can not be produced by traditional nanofabrication techniques. The fact that nanowires are made from a superconductor and form a loop makes them very sensitive to the magnetic field. This is because the magnetic field, as it is applied, induces an electrical current in the loop formed by two DNA-based superconducting nanowires. The current changes the sign periodically, between positive and negative, as the magnetic field increases. This particular fact is due to the quantum interference of two electronic waves passing through each wire. As a result, the device show an oscillation of its resistance with magnetic field. These oscillations are fundamentally different from previously know so-called Little-Parks oscillations. The device can be used as an ultrasmall detector of local variations of the magnetic field.

Education and collaborations: Eight undergraduate REU students have work on this project over the last few years. The list includes M. Murphey, A. Dibos, C- J Lo, M. Remeika, M. Boss, M. Murphey, S. Chu, and R. Colby. M. Remeika is currently a graduate student at our own department. S. Chu is a graduate student at Harvard University. M. Murphey and M. Boss are graduate students at Ohio state university. Anther former undergraduate student, R. Colby is currently a graduate student at Purdue University. Most of experimental work is done by a graduate student David Hopkins. He became a high- level expert in matters related to nanotechnolgy. Our theory collaborator, Paul Goldbart, is a professor at Physics department, UIUC. Broader Impact: The molecular templating technique, which uses DNA molecules, is very general and thus may have a strong impact on nanotechnolgy. The method can be used for fabrication of metallic, semiconducting, magnetic, and superconducting wires and arrays of wires for different types of nanodevices. The fact that the method is based on the application of DNA molecules shows that molecular biology can be employed for making novel and useful nanodevice, such as a quantum interferometers in our case. The work was cited by PhysicsWeb, Nanotech- Web, Semiconductor International and other media. Novel quantum interference device made of DNA-templated superconducting nanowires Alexey Bezryadin, University of Illinois at Urbana-Champaign, DMR The figure shows two nanowires suspended over the trench and supported by DNA.

Novel quantum interference device made of DNA-templated superconducting nanowires Alexey Bezryadin, University of Illinois at Urbana-Champaign, DMR There are many examples in which physics provides technical means for solving specific problems in biology and biology-related disciplines such as medicine. Here an alternative approach is suggested, in which biological methods are used to solving problems in Condensed Matter Physics. In particular a method is developed in which biological molecules act as scaffolds for ultra-small devices. The method is so general that it can be used for making magnetic devices for information processing technology, or superconducting device for extremely sensitive measurments of the magnetic field. The method is also useful because it offers a possibility of integrating of a large number of nanodevices into a single complex unit, using the ability of DNA to self-assemble into complex networks and constracts.