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Y. Yang et al.
10.4 Chirality at a Nanometer Scale: Bottom-Up Approach
Bottom-up techniques are versatile approaches to fabricate complicated nanostructures on a large scale [35–39]. These techniques have several advantages over topdown methods such as lithography and direct writing, which enable patterning of
predefined structures, but can fabricate only 2D or stacked 2D structures, and are
impractically expensive. On the contrary, bottom-up methods can fabricate truly-3D
structures at reasonable cost. Bottom-up techniques can arrange NPs in a complex
configuration with high precision and can fabricate complicated 3D geometry. They
can also use diverse components including plasmonic NPs, organic materials and
quantum dots. Dynamic tunability and programmability also make the bottom-up
methods a powerful tool to realize 3D chiral nanostructures. In this section, we
describe several such bottom-up techniques to make 3D chiral nanostructures and
describe their optical characteristics.
10.4.1 Molecular Self-assembly
Molecular self-assembly is a bottom-up approach that exploits spontaneous assembly
of inorganic materials such as metals, semiconductors, ceramics and biological materials including peptides, fibers and DNA [40, 41]. Synthesis from molecules in
solution gives rise to plasmonic NPs that have chiral morphology. NPs that had
broken mirror-symmetric geometry have been synthesized using thiolated chiral
biomolecules [42]. Tellurium and selenium bind strongly with the thiol group and
hence are transformed into chiral shape (Fig. 10.9a, b). Such NPs act as chiral
resonators and show polarization-dependent extinction rate in the visible spectrum
(Fig. 10.9c, d). The chiral tellurium nanostructures can be transformed into chiral gold
and silver telluride nanostructures that have very large chiroptical activity, demonstrating a simple colloidal chemistry path to realize chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to
interactions of chiral biomolecules with chiral inorganic surfaces, with relevance
to asymmetric catalysis, chiral crystallization and the evolution of homochirality in
biomolecules.
Chiral gold NPs can be synthesized with the aid of amino acids and peptides [43–
52]. During particle synthesis, amino acids and peptides interact with the particles
and produce twisted high-Miller-index surfaces (Fig. 10.9e). The handedness of the
input molecules determines the growth rates of chiral high-index planes that have
opposite handedness. Thus, the chiral morphology of the molecules is transferred to
the NPs (Fig. 10.9f). The chiral geometry of the NPs makes them interact differently
with LCP and RCP. CD is significantly increased near the resonant wavelength of
the gold NPs (Fig. 10.9g).
Chiroptical phenomena such as optical activity and CD do not necessarily require
chiral NPs. Achiral NPs that are arranged in a chiral pattern can also exhibit an
Y. Yang et al.
10.4 Chirality at a Nanometer Scale: Bottom-Up Approach
Bottom-up techniques are versatile approaches to fabricate complicated nanostructures on a large scale [35–39]. These techniques have several advantages over topdown methods such as lithography and direct writing, which enable patterning of
predefined structures, but can fabricate only 2D or stacked 2D structures, and are
impractically expensive. On the contrary, bottom-up methods can fabricate truly-3D
structures at reasonable cost. Bottom-up techniques can arrange NPs in a complex
configuration with high precision and can fabricate complicated 3D geometry. They
can also use diverse components including plasmonic NPs, organic materials and
quantum dots. Dynamic tunability and programmability also make the bottom-up
methods a powerful tool to realize 3D chiral nanostructures. In this section, we
describe several such bottom-up techniques to make 3D chiral nanostructures and
describe their optical characteristics.
10.4.1 Molecular Self-assembly
Molecular self-assembly is a bottom-up approach that exploits spontaneous assembly
of inorganic materials such as metals, semiconductors, ceramics and biological materials including peptides, fibers and DNA [40, 41]. Synthesis from molecules in
solution gives rise to plasmonic NPs that have chiral morphology. NPs that had
broken mirror-symmetric geometry have been synthesized using thiolated chiral
biomolecules [42]. Tellurium and selenium bind strongly with the thiol group and
hence are transformed into chiral shape (Fig. 10.9a, b). Such NPs act as chiral
resonators and show polarization-dependent extinction rate in the visible spectrum
(Fig. 10.9c, d). The chiral tellurium nanostructures can be transformed into chiral gold
and silver telluride nanostructures that have very large chiroptical activity, demonstrating a simple colloidal chemistry path to realize chiral plasmonic and semiconductor metamaterials. These materials are natural candidates for studies related to
interactions of chiral biomolecules with chiral inorganic surfaces, with relevance
to asymmetric catalysis, chiral crystallization and the evolution of homochirality in
biomolecules.
Chiral gold NPs can be synthesized with the aid of amino acids and peptides [43–
52]. During particle synthesis, amino acids and peptides interact with the particles
and produce twisted high-Miller-index surfaces (Fig. 10.9e). The handedness of the
input molecules determines the growth rates of chiral high-index planes that have
opposite handedness. Thus, the chiral morphology of the molecules is transferred to
the NPs (Fig. 10.9f). The chiral geometry of the NPs makes them interact differently
with LCP and RCP. CD is significantly increased near the resonant wavelength of
the gold NPs (Fig. 10.9g).
Chiroptical phenomena such as optical activity and CD do not necessarily require
chiral NPs. Achiral NPs that are arranged in a chiral pattern can also exhibit an