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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

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Ultrathin film preparations of single-walled carbon nanotube (SWNT) allow economical utilization of nanotube properties in electronics applications. Recent advances have enabled production of micrometer scale SWNT transistors and sensors but scaling these devices down to the nanoscale, and improving the coupling of SWNTs to other nanoscale components, may require techniques that can generate a greater degree of nanoscale geometric order than has thus far been achieved. Here, we introduce linker-induced surface assembly, a new technique that uses small structured DNA linkers to assemble solution dispersed nanotubes into parallel arrays on charged surfaces. Parts of our linkers act as spacers to precisely control the internanotube separation distance down to <3 nm and can serve as scaffolds to position components such as proteins between adjacent parallel nanotubes. The resulting arrays can then be stamped onto other substrates. Our results demonstrate a new paradigm for the self-assembly of anisotropic colloidal nanomaterials into ordered structures and provide a potentially simple, low cost, and scalable route for preparation of exquisitely structured parallel SWNT films with applications in high-performance nanoscale switches, sensors, and meta-materials.

Sodium carbonate (Na₂CO₃) presents a huge challenge to plants by the combined damaging effects of Na⁺, high pH, and CO₃²⁻. Little is known about the cellular responses to Na₂CO₃ stress. In this study, the transcriptome of maize (Zea mays L. cv. B73) roots exposed to Na₂CO₃ stress for 5 h was compared with those of NaCl and NaOH stresses. The expression of 8,319 genes, representing over a quarter of the total number of genes in the maize genome, was altered by Na₂CO₃ stress, and the downregulated genes (5,232) outnumbered the upregulated genes (3,087). The effects of Na₂CO₃ differed from those of NaCl and NaOH, primarily by downregulating different categories of genes. Pathways commonly altered by Na₂CO₃, NaCl, and NaOH were enriched in phenylpropanoid biosynthesis, oxidation of unsaturated fatty acids, ATP-binding cassette (ABC) transporters, as well as the metabolism of secondary metabolites. Genes for brassinosteroid biosynthesis were specifically upregulated by Na₂CO₃, while genes involved in ascorbate and aldarate metabolism, protein processing in the endoplasmic reticulum and by N-glycosylation, fatty acid biosynthesis, and the circadian rhythm were downregulated. This work provides the first holistic picture of early transcriptomic adaptation to Na₂CO₃ stress, and highlights potential molecular pathways that could be manipulated to improve tolerance in maize.

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