Page 511 - Book Hosokawa Nanoparticle Technology Handbook

16 NANOPARTICLE FORMATION OF DNA (GLOBULE TRANSFORMATION) APPLICATIONS

Figure 16.3
Coil–globule transition of DNA molecules by electrolysis of Al electrodes. Phase transition of T4 dc DNA due to
electrolysis was fluorescently observed. (a) DNA molecules around the solution–electrode interface before voltage
application. (b–d) Time-lapse photographs of the coil–globule transition of the DNA molecules. Dotted line in each
photograph indicates the aluminum ion front. Scale bars represent 10 m.

is a quite effective method to manipulate giant DNA globule DNA. The gradient force is also generated
without breakdown. by AC electric field because the gradient force
directs toward higher electric field regardless of its
direction. Application of AC electric field is quite
2. Micromanipulation of DNA nanoparticles effective to suppress electrolysis on electrodes,
which sometimes interferes manipulation due to
To analyze DNA molecules or to apply DNA mole- bubble production.
cules as templates for addressing nanoparticles, a Light, electromagnetic wave of extremely high fre-
target of single DNA molecules should be manipu- quency, also generates gradient force. This method,
lated and transported to intended positions for called as laser tweezers, permits non-contact micro-
suitable analysis or templates. Even though electric manipulation of particles; however, tapping force for
force is quite effective to manipulate small particles coiled DNA is quite small, and coiled DNA cannot be
such as DNA molecules, charge of globule DNA is manipulated by this method. So far, laser manipula-
almost canceled; therefore, Coulomb force cannot tion for coiled DNA was achieved by conjugation of
be applied for manipulation. Gradient force is coiled DNA and a microbead that was several microns
proportional to square of electric field gradient and in diameter. The conjugate of DNA–microbead can be
is much smaller than Coulomb force; however, this manipulated by laser tweezers or a needle magnet.
force acts on electrically neutral particles such as However, the conjugation method for long DNA is not

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