Binary Colloidal Alloy Test - 6: Polystyrene - Deoxyribonucleic Acid (BCAT-6-PS-DNA) attempts to produce crystals in microgravity where the components of the crystals are held together by deoxyribonucleic acid (DNA). The crystals in this experiment are created from DNA coated spherical polymer particles. The experiment has applications in the design of new revolutionary nanomaterials.Principal Investigator(s)
ZIN Technologies Incorporated, Cleveland, OH, United States
National Aeronautics and Space Administration (NASA)Sponsoring Organization
Human Exploration and Operations Mission Directorate (HEOMD)ISS Expedition Duration:
September 2010 - October 2013
25/26,27/28,29/30,31/32,33/34,35/36Previous ISS Missions
The BCAT predecessors, BCAT-3 operated on ISS, and BCAT, operated on Mir in 1997 and 1998. BCAT-4 launched March 11, 2008 on 1J/A, and BCAT-5 launched June 13, 2009 on 2J/A.
It is possible to use DNA as a type of glue that only bonds with pre-selected sites that have been coated with a complimentary type of DNA. When DNA type A is glued to one side of particles and DNA type A-prime is glued to the other side of particles, the particles should connect A to A-prime and form chains. This bonding can be made temperature dependent so that it only happens when the sample goes below a chosen temperature (~ 23 degrees C). By raising and lowering the temperature, a sample can be annealed (and become a better structure with each "freeze-thaw" cycle) since the appropriate partners will gradually find themselves closer to each other after each freeze-thaw cycle. Ultimately, more complex particles will be fabricated with connectors for both A and A-prime, B and B-prime, and so forth. This will allow nanotechnology to be geared up so that self-assembly can occur for things like nanopumps when lots of particles are dumped together. As Professor Paul Chaikin has said, "If you have one nanopump you don’t pump much fluid, but once you can self-assemble billions of them, now we’re talking."
New York University scientists synthesize polystyrene particles such that they all have virtually the same size. They then coat half of the particles with a precisely defined DNA composition. The other half receives a coating of DNA that intentionally sticks to the DNA on the other particles. For simplicity, refer to the two kinds of DNA as A and A’. The attraction between A and A’ brings the polystyrene particles together to form chains. If the binding is too strong the particles stick together in a clumsy way and fall out of solution without retaining the beauty of the crystalline order that is sought in this experiment. In order to avoid this, the investigators add precisely controlled quantities of detergent-like organic molecules and electrolytes to adjust the strength of the binding interaction to make the crystalline patterns. This is also how the scientists have designed the crystals to melt. The crystals melt when the system is heated to the right temperature. The crystals lose their periodic order and beauty when they melt into liquids. Their positions with respect to each other are more fluid and random when this event occurs. This process is reversible and the crystals can recrystallize after they melt often resulting in increased clarity and order.
The particles are adapted to melt within a six degree temperature range. When the space station moves in and out of light’s direct path from the sun, the sample heats and cools. These heating cycles melt and recrystallize the samples at the same regularity. The scientists then determine what crystal shapes and geometries are selected by the experimental parameters of the solutions.
This experiment addresses basic physics questions, but some of the areas may eventually have applications for self assembly of nanoparticles in space.Earth Applications
The technology now exists to produce bio-mimetic chemical systems with self-replicating non-biological structures from nanoscale building blocks using colloidal self-assembly. These studies lay the foundation for this process. The applications of this kind of work could lead to new display technologies, medical diagnostics, and many other possibilities in molecular nanotechnology.
The BCAT-6 consists of a set of ten small samples of colloidal particles. The BCAT-6 samples are each contained within a small case the size of a school textbook. The experiment requires a crew member to set up the experiment using a handrail/seat track configuration, ISS Laptop and the Kodak 760 or Nikon D2Sx camera to take digital photographs of the samples at close range. The pictures are down-linked to investigators on the ground for analysis.
The current plan for this experiment is to conduct it over a 7 or 14-day session, each of which can be run incrementally and require about 7 hours of crew time; a third session to mix and photograph all 10 samples (about 4.6 hours of crew time) and then a fourth session at six months to photograph all ten samples which is slotted to take about four hours of crew time. As such, new information will undoubtedly be learned, and the nature of the experiments conducted will evolve to take advantage of this new information.
BCAT-6 typical operations consists of:
Session 1: Set up hardware, take baseline photos of all ten samples; homogenize samples 6-10 then samples 9 and 10, then automatically photograph sample 1 (using EarthKAM software on laptop) every hour for 7 days. Perform sample 1 daily status check each day. After seven-day run, perform crystal search/photography on 6-10. Homogenize sample 2, automatically photograph sample 2 (using EarthKAM software on laptop) every hour for 7 days. Perform sample 1 daily status check each day. After seven-day run, perform crystal search/photography on 6-10. If necessary, tear down after operations are complete but keeping setup intact is preferred to save crew time.
Session 2: Set up hardware, homogenize samples 3, 4 and 5 one at a time then automatically photograph each sample (using EarthKAM software on laptop) every hour for 14 days each. Perform Crystal Check and Photography procedures on 6-10 if crystals not found/photographed in Session 1. If necessary, tear down after operations are complete but keeping setup intact is preferred to save crew time. .
Session 3: Homogenize and photograph samples 1-10 (using EarthKAM software on laptop) and stow sample module for six months. The experiment is torn down after operations are complete. .
Session 4: At six months after homogenization, manually photograph Ssamples 1 through 10. Re-stow sample module and tear down after operations are complete.