Biomedical Engineering Reference
In-Depth Information
In experiments on plasmonic structures, we have observed
enhancedCDinthemolecularband[8].Inaddition,itwassuggested
that an enhanced vibrational molecular CD in the infrared band
is able to show more details of molecular structures [22]. Our
general conclusion is that the amplification of the molecular CD
requires special efforts in the design and fabrication. For example,
anisotropy of a chiral nanostructure can be crucial for creation of
strongplasmonicCD.Inparticular,wehaveshowntheoreticallythat
enhanced molecular CD appears for oriented molecules attached
to a metal NP [31, 32]. Also, a metal NP dimer, which is a highly
anisotropicnanostructure,isagoodcandidatetoenhancemolecular
CD signals due to a strong field enhancement effect in a plasmonic
hot spot [32]. A hot spot effect in such a dimer structure can more
effectively enhance the molecular CD when the NPs approach each
other closely [81]. However, a hot spot effect from random NP
aggregates generally needs to be verified carefully, as complicated
features may appear in the CD spectra. Stronger anisotropy can
be generated by introducing 3D chiral NCs or assemblies. The
consideration of the optical chirality factor in this chapter led us to
thegeneralconclusionthatthenear-fieldenhancementandtwisting
effectsinlightbeamsshouldbecombinedinsensingofbiomolecules
[62].
Despiteseveralinterestingrecentdevelopmentsandpotentialof
chiral NCs for future applications, the fabrication of artificial chiral
nanostructuresisstillinitsinfancyandremainschallenging.Inpar-
ticular, more efforts are needed to achieve the structural yield and
homochirality of NCs in an ensemble. Nowadays, the technologies
available to construct chiral nanomaterials may be divided into two
categories. In the first category, the nanostructures are assembled
on an atomic level. This will include metal/semiconductor nano-
clusters either with an intrinsic chiral structure or a surface chiral
molecular adsorption. In the second category, on which this chapter
is mostly focused, the fabrication incorporates nanomaterials that
interact through electromagnetic interactions. The building blocks
are better defined and the techniques of assembling the nanostruc-
tures are more generic and easier to adapt to new applications.
InformativereviewsareavailableinRefs.[28,73],whichintroduced
the self-assembly technologies to create NP structures through
