Biomedical Engineering Reference
In-Depth Information
interesting example—chiral tetrapods. These NCs also exhibited CD
signals at the excitonic transitions [29]. Detailed studies on a size-
dependence of CD signals of chiral bio-conjugated QDs can be found
in Ref. [5].
Here, it is important to mention another very recent study on
the QDs with an intrinsically chiral crystal structure [4]. Although
the various plasmonic or excitonic NPs interactions with chiral
molecules lead to small CD induction effects, as mentioned above, a
different concept that may lead to large chiroptical effects for single
NPs would be to use certain types of inorganic materials that form
chiral crystals, that is, their lattices correspond to chiral symmetry
Figure 1.27
(a,b) High-resolution transmission electron microscopy im-
ages showing the single crystal nature of the
α
-HgS NCs. The long axis is
alwaysidentifiedasthec-axis,whichistheaxisofthehelicalHg-Sspirals,as
sketched in (c), which schematically shows the unit cell structure of these
crystals. (d) A comparison of the dissymmetry factor at the first exciton
transition for NCs of four different semiconductor NCs at various sizes as
afunctionofsurface/volumeratio(1/
r
),where
r
istheNCradius.Inachiral
semiconductors, the surface-sensitive CD induction strongly decays with
r
,
contrary to the intrinsically chiral
α
-HgS, wherein relatively large particles
exhibitlargedissymmetry.AdaptedwithpermissionfromRef.[4].Copyright
c
2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
