Page 39 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 3 – Internet of Bio-Nano Things for health applications

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 3

Polarizer Analyzer
In general, chirality transfer occurs through chemical
EM pulse bonds, but recently it has been observed that chiral
biomolecules may impart some of their optical proper‑
ties to a spatially separated achiral dye [9]. Knof and von
Zelewsky [10] have characterized the chiral transfer as
Non-polarized EM field Polarized
EM field Chiral channel Rotation of through the use of organic ligands chiral information can
polarization plane
be transferred.
Fig. 2 – Property of rotation of the polarization plane of an EM pulse
impinging a chiral channel.
In the context of chirality transfer it is important to high‑
light chiroptical properties. Among the most important
EM ield both clockwise and counterclockwise. If the ro‑ properties are the chiral luminescent lanthanide com‑
tation is clockwise, chiral molecules are said to be dextro‑ plexes used as probes for the characterization of chiral
rotary, and correspond to positive rotation values, while environments [11, 12, 13] or as chiral luminescent com‑
chiral molecules rotating the plane of polarization coun‑ plexes [14, 15, 16, 17]. Lanthanides are ideal candi‑ dates
terclockwise are said to be levorotary, and correspond as luminescent probes, based on speci ic features such as
with negative values of the speci ic rotation. their long lifetimes and large Stokes shifts. CP
Another important feature of chiral molecules is the chi‑ luminescence has great potential to investigate the con‑
rality transfer that occurs when a chiral molecule encoun‑ igurational, as well as conformational changes, in bio‑
ters an achiral molecule. In such a scenario, the chirality logical systems in solution, since it combines the gen‑ eral
effect is extended over the whole molecular system i.e., it sensitivity of luminescence measurements and the high
propagates from a chiral to an achiral molecule, which be‑ speci icity of the signal for the chiral environment.
comes chiral. The induction of the chirality in the achiral Furthermore, using very simple chiral ligands and lan‑
components is of utmost importance. In order to induce thanide ions, chiral nanoballs were obtained where the
the chirality of the achiral components, the interaction array of lanthanide ions are arranged as in the ferritin bi‑
between the chiral molecules and the achiral molecules ological molecule [18, 19]. With very simple chiral lig‑
plays a very important role. ands used as synthons (i.e., a synthon is a component of a
The induced chirality generally refers to those chiral molecule to be synthesized, playing an active role in
supramolecular systems where chirality is induced in an synthesis) in coordination chemistry, it is possible to ob‑
achiral guest molecule as a result of asymmetric informa‑ tain sophisticated chiral assemblies which mimic biologi‑
tion transfer from a chiral host e.g., a chiral molecule or cal systems. These considerations are encouraging in the
a chiral nanostructure. In order to produce the induced development of “arti icial” molecular communication sys‑
chirality, it is necessary for the achiral molecule to have tems.
a strong interaction with the chiral host through a non‑ Chirality is also important in molecular switches [20, 21].
covalent bond. A typical example of induced chirality is A switch is a molecule that can reversibly interconvert
the encapsulation of a chromophore into the cavity of cy‑ be‑ tween two stable states upon an external stimulus. In
clodextrin [7]. Finally, a very important aspect related [22] Dai et al. described a chiroptical switch based on
to chirality is the chiral communication that is a common pho‑ tochromes that exhibit two different states with
phenomenon occurring in many biological processes [8], signi i‑ cantly different optical rotations. Finally, chiral
strictly tied with the chirality transfer property. transfer phenomena can be used for sensing chirality of a
In this paper, we will exploit the chirality transfer effect wide range of chiral molecules, as well as for developing
by the means of diffusion of chiral molecules which come novel chiroptical devices and chiral materials.
into contact with achiral molecules in a biological solu‑ The wider application of chiral sensing continues to be
tion. hampered by the involved chiral signals being inherently
weak. To avoid this issue, plasmonic and dielectric nanos‑
3. CHIRALITY TRANSFER EFFECT tructures have recently been shown to offer a viable
route for enhancing weak circular dichroism (CD) effects.
As already introduced in Subsection 2.1, the chirality transfer Re‑ cently, in [23] Mohammadi et al. presented an
effect is observed between organic and inorganic molecular analytical study of the problem of substrate CD
structures. The modeling of macroscopic chi‑ rality emerged spectroscopy for an arbitrary nanophotonic substrate
from the chiral molecular elements is a challenge for theory,
(either, chiral or achi‑ ral, plasmonic or dielectric) and
computations, and experiments. Nu‑ merous experimental
clarify the interplay be‑ tween key affecting parameters,
results demonstrated the transfer of chirality among different
such as the thickness and chirality of the substrate, as
length scales ranging from di‑ mensions of the elementary
well as the near‑ ield optical chirality enhancement. From
particles to the macro‑scale (i.e., the length of the axon). In
particular, it was shown that the chirality at the molecular the telecommunications point of view, chirality
scale (i.e., amino acids, proteins, and polysaccharides) could be transfer can be exploited by the means of a diffusion
transferred to the macroscopic and macro level (i.e., process of the chiral molecules.
neuro ilaments and in‑organic crystals). When the “chirality effect” is transferred to an achiral
molecule and an optical signal is applied, it will be able to

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