Biomedical Engineering Reference
In-Depth Information
Figure 1.15
The plasmonic CD band of Ag NPs assembled on DNA (a) and
the geometry of the system including a TEM image of the Ag NP chain
(b). Reprinted with permission from Ref. [65]. Copyright 2006, American
Chemical Society.
these experiments, silver ions were complexed with nucleic acids
and reduced from the solution. DNA served as a template for the
growth of silver NPs. The resulting complex is shown in the TEM
image in Fig. 1.15b. Interestingly, the CD signal of DNA at 260 nm
wasinversed,whileanewCDbandwascreatedintheplasmonband
asshowninFig.1.15a.Inacontrolexperiment,itwasshownthatno
plasmonic CD could be provoked by merely mixing DNA molecules
and premade silver NPs. It was concluded that DNA had directed
the asymmetric growth of silver NPs [65]. Now we know that the
asymmetry can be in the overall geometry of the assembly or stem
from surface distortions on the NPs. It has to be noted that the
plasmonicCDcanalsocomefromtheothermechanismssuchasthe
orbital hybridizationor the exciton-plasmoninteraction.
Previously, it was proposed that both plasmon-plasmon and
plasmon-exciton interactions could induce CD signals at plasmon
bands. In order to see the physical pictures more clearly, alternative
designs of nanostructures were realized in the following experi-
ments.
On colloidal AuNPs coated with chiral peptides [67], a moder-
ately strong plasmonic CD signal can be identified from the spectra
of E5-AuNP in Fig. 1.16 and of FlgA3-AuNP that can be found in Ref.
[67]. This induced CD signal was attributed to the plasmon-exciton
interaction. An
-helical peptide (E5) has a stronger dipole moment
than an unstructured peptide (FlgA3). Therefore, the
α
α
-helical
