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
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.
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