A nanomechanical molecular “tape reader” is assembled and tested by threading a β-cyclodextrin ring onto a DNA oligomer and pulling it along with an AFM tip. The formation and mechanical operation of the system is confirmed by measuring the forces required to unfold secondary structures in the form of hairpins. Unfolding induced by this 0.7 nm aperture requires 40 times more force than that reported for pulling on the ends of the DNA. A kinetic analysis shows that much less strain is required to destabilize the double helix in this geometry. Consequently, much more force is required to provide the free energy needed for opening. DNA secondary structure may prove to be a significant obstacle both for enzymes that process DNA though an orifice, and for the passage through nanopores proposed for some novel sequencing schemes.

Guanidinium ions tethered to an electrode form electrical contacts to DNA via hydrogen bonding with the backbone phosphates, thus providing a sequence-independent electrical connector for native DNA submerged in an aqueous electrolyte. DNA adlayers on a guanidinium modified electrode can be imaged by scanning tunneling microscopy with tens of pS gap conductance. The image resolution suggests that multi-atom contacts contribute to the tunnel conductance, so we estimate that the single-nucleotide pair conductance may be on the order of 1 pS.

in the classroom Students step upUniversities and institutions in the United States are getting ready to celebrate nanotechnology and its achievements for National Nanotechnology Day. Lisa Friedersdorf, Quinn Spadola and Brendan Ryan share students' plans for the occasion.

This paper discusses part of the NSF funded project, CareerWISE: Internet-Delivered Resilience Training to Increase the Persistence of Women Ph.D. Students in STEM Fields. Research shows that rates of doctoral student attrition (i.e., beginning and then not completing a doctoral degree program) are substantially higher for women than for men, including in the physical sciences and engineering. The CareerWISE project addresses this problem through the development of a web-based resource consisting of training materials that will build the resilience skills, problem solving skills, and persistence of women in science and engineering PhD programs. CareerWISE is currently in the second of three years, and this paper focuses primarily on the portion of the project involving written case studies. The differences between the types of case studies traditionally used in science and engineering courses and the CareerWISE case studies are discussed, along with the plans for evaluating and integrating the cases with the other pieces of the CareerWISE project.Index Terms -Case Studies, Doctoral Student Retention, Women in Science and Engineering.