Managing Hierarchical Supramolecular
Organization with Holographic Tweezers
M. Woerdemann, A. Devaux, L. De Cola and C. Denz
Hierarchical supramolecular organiza- tion may be key to designing novel,
functional organic or inorganic materials
with tailored properties that exploit the
strong relationship between molecular
arrangements and resulting macroscopic
properties. 1 In particular, the hierarchical
organization of pre-ordered structures is
one of the most promising approaches to
bridging di;erent ordering scales—from
the molecular to the macroscopic.
Microporous molecular sieves such
as zeolites have proven to be ideal host
materials to accommodate a wide range
of guest molecules2 and thereby realize a
first level of organization. ;e challenge
is to create ordered assemblies of the host
material after they are loaded with guest
species, thus creating hierarchical supramolecular organization. ;ere are several
examples of relatively simple, large-scale
organization of host materials with
established chemical methods. So far,
however, it has been almost impossible
to achieve a higher degree of fine control
on the level of the single host particles.
Where chemistry reaches its limit,
optics takes over. Optical tweezers are
ideal tools for a moderate number of
particles; they can trap, orient and guide
particles, particularly when holographic
optical tweezers (HOT) are implemented. 3 Creating optical landscapes to trap
a larger number of particles in 3-D in
a defined and preferably reconfigurable
way is still a challenge, especially for
objects with nonspherical symmetry.
Earlier this year, we showed that it
is possible to achieve a high degree of
control on elongated microscopic objects
like rod-shaped bacteria by means of tailored light fields in HOT. 4 Transferring
this approach to zeolite-based host-guest
materials—which also have a nonspherical shape—we can create almost arbitrary
configurations. 5 With HOT, any single
host in an assembly can be controlled
independently from all others, solely by
(a) Optically induced organization of multiple zeolite L host particles. The setup is based on a Nikon Ti Eclipse microscope where holographic tweezers are implemented by means of
a 2.5-W Nd:YVO4 laser (l= 1,064 nm), which illuminates a high-de;nition phase-only spatial
light modulator. After the light ;eld is structured, it is focused through the microscope
objective (M=100x, NA= 1. 49) and thus creates the desired con;guration of multiple optical
traps at different transversal and axial positions. (b) Sixteen polydisperse zeolite L particles
with diameter and length of roughly 1 µm are 3-D optically trapped in a rectangular lattice
con;guration and sorted by size. (c) The complexity of organization is increased by adding
additional zeolite L particles at the geometrically relevant positions, resulting in a centered
rectangular lattice. Black insets show the con;guration of the optical traps (white spots).
optical means and in strong contrast to
the contemporary, ensemble-based methods. As the sample is observed through an
inverted, optical fluorescence microscope
during operation, all manipulations can
be done truly interactively.
Any host particle with desired proper-
ties can be selected separately from a
reservoir and precisely translated to
any position in the microscopic sample,
thereby allowing hundreds of hosts to be
held simultaneously. ;e most power-
ful advantage of our optical approach,
however, is that it allows the possibility
of rotating elongated host particles into
any orientation with highest precision
by means of optimized light fields that
create multiple traps with di;erent
relative intensities. ;is formidable level
of control allows for the realization of
tailored microstructures with a widely
tunable degree of organization.
to view the video that accompanies
M. Woerdemann ( email@example.com) and C.
Denz are with the Westfälische Wilhelms-Universität
( W WU), Münster, Germany. A. Devaux and L. De Cola
are with the W WU and Center for Nanotechnologie.
1. J. A. A. W. Elemans et al. J. Mater. Chem. 13, 2661-70
2. D. Bruhwiler and G. Calzaferri Micropor. Mesopor. Mater.
72, 1-23 (2004).
3. G. Sinclair et al. Opt. Express 12, 5475-80 (2004).
4. Hörner et al. J. Biophoton. 3, 468-75 (2010).
5. Woerdemann et al. Adv. Mater. 22, 4176–9 (2010).
40 | OPN Optics & Photonics News