Design and formation of the linker complex. Oligos were purchased in lyophilized form from IDT DNA. Sequences are below. LNA nucleotides are written as +C+G+A, etc. All other nucleotide are DNA. Labeling domain sequences were computer-optimized (31) to minimize sequence complementarity, homology, and melting temperature differences with programs written in MATLAB available at:http://www.dna.caltech.edu/DNAdesign/ Red linker main strand:Red linker protection strand:Blue linker main strand: 5ʼ TTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTTATACGGGGCTGGTTA+G+G+A+T+G 3ʼBlue linker protection strand: 5ʼ TAACCAGCCCCGTAT 3ʼStrands are separately dissolved in water purified by a Milli-Q unit (Millipore) to form stock solutions at ∼300 µM. A 2 M NaCl stock solution is created and filtered using 0.22 µm filters. For the red (blue) linker complex, the main strand and the protection strand are mixed with NaCl stock solution and Milli-Q purified water to obtain 600 µL of dispersal solution with ∼ 33 µM of the main strand, ∼ 36 µM of the protection strand, and 0.1 M NaCl; the concentrations of the main and protection strands were chosen to give a 10% excess of protection strand. This solution is put in a 0.6 mL PCR tube and annealed in an Eppendorf Mastercycler from 95• C to 20• C at 1 • C per minute. The protection strand/main strand partial duplex has a melting temperature T melting ∼50• C in our buffers. Dispersal of SWNTs.To create the red (blue) NL-SWNTs, ∼1 mg of dry HiPco SWNTs are added to 400-600 µL of the dispersal solution in a 1.7 mL PCR tube. The tube is then placed in an ice-water bath and sonicated for ∼90 minutes in a Branson 2510 sonicator (100 W). The water level inside the sonication chamber and the position of the PCR tube is adjusted to apply maximum sonication power to the sample. The temperature of the water bath is maintained at ∼15• C. The SWNTs are sonicated until the solution turns a uniform gray color and all the SWNTs are completely solubilized. The solution is then centrifuged at 16,000 g for 90 min at 15• C. Following this step, the supernatant is retained while the insoluble condensate is discarded. This process yields a high concentration of well-dispersed NL-SWNTs as determined by AFM and TEM images.1

Direct-write 3D printing enables the fabrication of three-dimensional objects via the extrusion from a nozzle. Stimuli responsive materials that shear-thin are well-suited as inks for these 3D printing systems. Poly­(isopropyl glycidyl ether)-block-poly­(ethylene oxide)-block-poly­(isopropyl glycidyl ether) ABA triblock copolymers were synthesized using controlled ring-opening polymerization to afford dual stimuli-responsive polymers that respond to both shear forces and temperature. These polymers were demonstrated to form hydrogels in water. The gels were observed to be thermoreversibledriven by the lower critical solution temperature of the poly­(isopropyl glycidyl ether) block which helps facilitate loading of the ink into the printer syringe. Rheological studies demonstrated that the gels had a rapid and reversible modulus response to shear stress. Thus, these materials were suitable as inks for direct-write 3D printing, as they were easily extruded during printing and maintained sufficient mechanical integrity which was necessary to support the next printed layer. Printed structures of high aspect ratio pillars and stacked layers were successfully demonstrated. These types of 3D hydrogel structures may ultimately have an impact in the biomedical field for applications such as tissue engineering.

Precise fabrication of semiconducting carbon nanotubes (CNTs) into densely aligned evenly spaced arrays is required for ultrascaled technology nodes. We report the precise scaling of inter-CNT pitch using a supramolecular assembly method called spatially hindered integration of nanotube electronics. Specifically, by using DNA brick crystal-based nanotrenches to align DNA-wrapped CNTs through DNA hybridization, we constructed parallel CNT arrays with a uniform pitch as small as 10.4 nanometers, at an angular deviation <2° and an assembly yield >95%.

We have determined the thermal resistance for transferring heat between individual single-walled carbon nanotube devices and solid substrates. Using sapphire and comparing our results to previous results obtained from SiO 2 , we find that the resistance is dominated by interfacial resistance rather than the spreading resistance of heat for diffusing into the substrate. Our results are in agreement to a recent model for the thermal resistance of nanoscale constrictions. Our results suggest that relatively short contact lengths ͑ϳ10-30 nm͒ to a typical solid should be sufficient to transfer heat efficiently into carbon nanotubes, underscoring the potential of carbon nanotubes for nanoscale thermal management.

With the increased prevalence of antibiotic-resistant infections, there is an urgent need for innovative antimicrobial treatments. One such area being actively explored is the use of self-assembling cationic polymers. This relatively new class of materials was inspired by biologically pervasive cationic host defense peptides. The antimicrobial action of both the synthetic polymers and naturally occurring peptides is believed to be complemented by their three-dimensional structure. In an effort to evaluate shape effects on antimicrobial materials, triblock polymers were polymerized from an assembly directing terephthalamide-bisurea core. Simple changes to this core, such as the addition of a methylene spacer, served to direct self-assembly into distinct morphologies-spheres and rods. Computational modeling also demonstrated how subtle core changes could directly alter urea stacking motifs manifesting in unique multidirectional hydrogen-bond networks despite the vast majority of material consisting of poly(lactide) (interior block) and cationic polycarbonates (exterior block). Upon testing the spherical and rod-like morphologies for antimicrobial properties, it was found that both possessed broad-spectrum activity (Gram-negative and Gram-positive bacteria as well as fungi) with minimal hemolysis, although only the rod-like assemblies were effective against Candida albicans.