Biomod/2012/Titech/Nano-Jugglers/Methods/Azobenzene Tweezers

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    The duplex-forming activities of DNA can be photomodulated by incorporation of an azobenzene unit. The duplex is dissociated on isomerizing the trans-azobenzene to the cis form by irradiation with UV light. The duplex is formed again when the cis-azobenzene is converted to the transazobenzene by irradiation with visible light.
We inserted this function into a bead-body and add the photo-switching function to the body.In brief, so that we can detached the engines by irradiation with UV light, we attached a part of engines to the body with DNA duplex incorporating azobenzene unit.

1.Designe DNA Incorporating 4 Azobenzenes

Image1 in detail

  • 5’ -(HS)-AATxACxCCxAGxCC-3’ (x=azobenzene)

1.We incorporated 4 azobenzene units into 11 bases DNA so that we can quickly dissociated DNA duplex.
2.5’ end of this DNA was modified by a thiol group(HS-) for forming Au-thiol bond with Au covered bead body.

Image2 in detail

  • 5’-(HS)-GGCTGGGTATT-3’

1.This 11 bases DNA are a complementary sequence of DNAⅰ(photoresponsive DNA).
2.5’ end of this DNA is modified by a thiol group(HS-) for forming Pt-thiol bond with Pt.

2.Ascertain the photo-switching system

Image3 in detail

  • Spectrophotometer
    We measured DNA absorbance and ascertain the duplex-forming and duplex-dissociation activities of DNAⅰ and ⅱ. As the ordered regions of stacked base pairs in the DNA duplex are dissociated, the UV absorbance increases. This difference in absorbance between the duplex and single strand state is the result of nearest neighbor base pair interactions. In other words, when the DNA is in the duplex state, interactions between base pairs decrease the UV absorbance relative to single strands. When the DNA is in the single strand state the interactions are much weaker,due to the decreased proximity, and the UV absorbance is higher than the duplex state[image3].
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