Biomod/2013/North Carolina State University/Procedure

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Procedure

Functionalizing the Gold Nanorods and Quantum Dots

Our first steps are to coat the gold nanorods and quantum dots with single stranded DNA in order to bind them to the origami. Our gold nanorods are orginally coated with a surfactant called CTAB to prevent aggregation while our Quantum Dots are suspended in Toulene. Mercaptoethanol is added to the quantum dots to make them water soluble then both the gold rods and the quantum dots are spun down and resuspended in water. Resuspend twice for good measure.

Now that the particles are water soluble and the excess surfactant has been removed, add 5000 thiolated oligonucleotides per gold nanorod and 3000 thiolated oligonucleotides per quantum dot. Both sets of particles should be kept at room temperature and mixed at approx 300 rpm throughout the next step. To facilitate binding slowly bring the salt concentration of the gold rods up to .5M and up to .1M for the quantum dots. This is to facilitate the DNA landing on the particles. Be careful not to add the salt too quickly as it will cause aggregation. It is recommended that the NaCl be added in thirty minute intervals in .015M increments.

Now the gold nanorods and quantum dots are ready to be added to the origami. Addition of the gold nanorods, quantum dots, and edge staple strands followed by an anneal yeilds our heterodimer.

heterodimer

Electrospinning

Previous work conducted by Dr. Tracy of North Carolina State University demonstrated that gold nanorods suspended in a polymer aligned themselves parallel to the axis of the polymer fiber after undergoing electrospinning. After constructing our heterodimers we suspend them in Polyethylene Gycol (PEO). We then electrospin them to produce fibers of diameter 15 micrometers. The heterodimers are aligned parallel to the axis of the fiber due to the electronic effects of the large voltage used to electrospin the polymer. The double stranded DNA strands (kite-tails) orient the heterodimers head to tail due to the increased drag experienced while drawn out into a fiber. This creates an ordered array within the polymer fibers. Placing the polymer fibers parallel to each other creates a macroscopic array of these nanoscale heterodimers.

electrospin

Previous work demonstrated that that when gold nanorods are distributed parallel to the polymer axis within a fiber that they demonstrate a selective adsorption of infrared light leading to a photothermal heating effect that can melt the polymer strands. This only occurs with infrared light that is polarized along the gold nanorods longitudinal axis as it corresponds to the longitudinal plasmonic frequency of the gold rod. When coupled with the quantum dots we believe that this arrangement will be able to step light down to a lower frequency.

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