Nano-Bio Integration - Bionanoelectronics: Bioinquiring and Bioinspired Devices - page 236

In contrast, graphene sheet suspensions obtained by reduction of graphene oxide
aqueous suspensions in the absence of ssDNA aggregate within 30 min. The stable
and highly negatively charged ssDNA-graphene sheets can be used for fabricating
lamellar self-assembled bionanocomposite materials intercalating, for example,
layers of the positively charged cytochrome c metalloprotein. A recent review on
the strategies for biohybrid fabrication, including lamellar structures, can be found
in Ruiz et al. ( 2010 ).
Biomolecules can also improve the performances of optoelectronic materials, in
particular organic dyes. Organic dyes embedded in thin polymeric films are used in
lasers, amplifiers, sensors, and displays due to their low cost, ease of fabrication, and
wavelength control, but these advantages are hampered by the tendency of organic
dyes to form nonfluorescent aggregates and to photodimerize and photooxidize
after repeated excitation. A possible solution to increase the photostability of
organic dyes is to encapsulate them in DNA thin films, as shown in Ner et al.
( 2009 ) for the nonlinear optical dye Hemi-22. DNA can become soluble in organic
solvents if layers of DNA and the cationic surfactant hexadecyltrimethylammonium-
chloride (CTMA) are assembled in a three-dimensional lamellar structure. Then,
thin films are fabricated by spin coating from dye solutions containing DNA-CTMA
assembles. DNA-CTMA prevents the formation of H-type aggregates in thin films
with dye loadings up to 10% (w/w) without altering the absorption spectrum of
Hemi-22. The DNA-CTMA lamellar structure increases also the photophysical and
photochemical properties of Hemi-22 films, enhancing in particular the stability
at UV illumination. The reason is that DNA absorbs UV light but also that dye
molecules in thin films bind with DNA base pairs in the polar microenvironment
assured by the DNA grove, binding which explains the redshift of absorption and
emission spectra compared to dye spectra in nonpolar solvents.

9.2 Nano-bio Mechanical Devices

An example of a hybrid nano-bio mechanical device is the nanomotor fabricated by
attachment of flagella separated from the biflagellate Chlamydomonas reinhardtii
unicellular alga to polystyrene microbeads ( Mori et al. 2010 ). The flagella are in
fact molecular motors with, in this case, dimensions of 12m in length and 200 nm
in diameter, which have controllable on/off states and are easier to prepare than
artificial molecular motors. The flagella tips attach nonspecifically, and therefore,
the surface of beads do not need to be functionalized in order to be propelled by
flagella. Experiments showed that the beads perform a uniform rotation about their
axes when one flagellum is attached to their surface and can advance if two flagella
are attached. A flagellum imparts a torque to the bead, the resultant torque from
two flagella vanishing, and hence, the resultant velocity becoming maximum, when
the angle between flagella is 1.4 rad. This value is close to =2, which represents
the angle between the two flagella for which the theoretical probability of their
attachment to the bead is maximum.