By Marinella Striccoli
Colloidal chemistry allows the fabrica- tion of metal, semiconductor, oxide, and magnetic nanocrystals (NCs) with well-controlled sizes and shapes, as well as of heterostructures with exotic shapes and composition (1). Such NCs
are promising materials in several techno-
logical fields. For example, the high-purity
emission color of semiconductor NCs has
been applied in optical displays (2), and their
broadband absorption has been exploited in
innovative solar cells (3). Other applications
include field-effect transistors, light-emitting
diodes, and sensors (4). However, for the fab-
rication of advanced electronic devices in a
parallel and scalable fashion for industrial
production, NCs must be integrated into
structures to bridge the gap between the
nano- and mesoscopic regimes (5). Thus, the
organization of NCs in morphologically con-
trolled patterns and processable systems is of
paramount importance. On page 385 of this
issue, Wang et al. (6) present a pioneering
and straightforward approach for the pat-
terning of functional inorganic NCs on sub-
strates with optical lithography. This advance
could add—literally—a multilayer dimension
to the development of NC-based devices.
The manufacturing of consumer electronics requires the fabrication of integrated
circuits (ICs). For this purpose, metals,
semiconducting, and oxide materials are
typically patterned by means of ultraviolet
(UV) lithography, a photographic process.
A light-sensitive material (a photoresist)
is exposed and developed to form three-dimensional (3D) structures or patterns
on a substrate. The photoresist is mainly
composed of photosensitizers, polymers,
solvents, and additives and can be positive
or negative, depending on whether it became soluble or insoluble to the developer,
respectively, after exposure to light.
Surface chemistry of all-inorganic nanomaterials
enables three-dimensional patterning
2 Light hardens exposed nanocrystal solution (red areas)
3 Mask is removed
4 Unexposed solution is removed
5 Nanocrystal pattern is created
3D view 3D view
Top view Top view
Multiple layers can be patterned sequentially, obtaining all-inorganic 3D structures with vertical
resolution of a few nanometers.
is the large dynamic movement (up to
~200-nm expansion in one direction or approximately fivefold aspect ratio change)
brought about by a small set of triggers (as
few as five DNA strands). In the largest relay array, 160 reconfigurable units communicate their structural information through
more than 300 flexible joints. Interestingly,
squarelike DNA antijunctions that are unstable by themselves exist in relay arrays as
bridges between rhombic units of different
conformations, which are elegant examples
of stabilized structure-switching intermediates. In addition, the information relay is
generalizable in 3D; rolling up a sheet of relay array yields a DNA tube that can change
its diameter and length simultaneously.
Although a few limitations of the system
remain to be resolved (such as the slow
transformation kinetics and the requirement of denaturing conditions), the reconfigurable DNA arrays are extremely exciting
because they present enormous possibilities. For DNA nanotechnology specialists,
the relay arrays provide a platform with
which to model the cooperative dynamics of
DNA junctions. Integrating the relay mechanism into other DNA nanostructures may
generate biologically relevant motions, such
as the rotary and swinging motions of flagella and cilia. For developing applications,
one could place guest molecules (for example, fluorophores, nanowires, or enzymes)
on the DNA arrays (9) and thus convert the
mechanical movement into optical, electrical, or chemical signals. Such constructs
may be useful for sensing biomolecules
and studying their collective dynamic behaviors. Last, with the rapid development
of DNA nanostructure–based membrane
engineering methods, it may be possible to
interface the dynamic DNA arrays with artificial or biological membranes. One could
envisage making expandable DNA nano-pores across lipid bilayers (10), constricting liposomes templated by DNA tubes (11),
and clustering cell surface receptors to elicit
functional responses (12). j
1. J. Song etal .,Science 357, eaan3377 (2017).
2. N. C. Seeman,Nature 421, 427 (2003).
3. F. Hong, F. Zhang, Y. Liu, H. Yan, Chem. Rev. 10.1021/acs.
4. J.Bath,A.J. Turberfield, Nat. Nanotechnol. 2,275(2007).
5. A. E. Marras, L. Zhou, H. J. Su, C. E. Castro, Proc.Natl.Acad.
Sci. U.S.A. 112, 713 (2015).
6. S. M. Du, S. Zhang, N. C. Seeman, Biochemistry 31, 10955
7. P. W. Rothemund, Nature 440, 297 (2006).
8. Y. Ke, L. L. Ong, W. M. Shih, P. Yin, Science 338, 1177 (2012).
9. F. A. Aldaye, A. L. Palmer, H. F. Sleiman, Science 321, 1795
10. S.Howorka, Nat. Nanotech. 12,619(2017).
11. Z. Zhang, Y. Yang, F. Pincet, M. C. Llaguno, C. Lin,Nat.
Chem. 9, 653 (2017).
12. X. Su et al., Science 352, 595 (2016).
Institute of Physical and Chemical Processes–Unit of Bari
CNR (CNR-IPCF), c/o Chemistry Department,
University of Bari, Via Orabona 4, 70126 Bari, Italy.
Direct nanocrystal patterning
Optical patterning of nanocrystals can add a third dimension to traditional microlithography. Wang et al. modify
the surface chemistry of nanocrystals with photoactive inorganic ligands to fabricate resists from solution that
can be easily microstructured.