General Overview: Researchers
at the Wisconsin MRSEC are working to develop sensors that can detect toxic
substances near a single cell by exploiting the unique properties of liquid
crystals (LC). LCs are materials that
combine physical properties of both liquids and solids, and they have been widely
used for displays (LCDs) in electronic devices because the LCs reorganize in
response to external stimuli such as electric fields. Recently, Wisconsin MRSEC
researchers discovered a method to encapsulate or “cage” tiny LC droplets
inside a polymer capsule. When the encapsulated
LC droplets are exposed to external stimuli, such as small cell-toxic molecules,
the LC reorganizes inside the cage resulting in changes in visual appearance
(see Figure). This advance, combined
with methods to engineer the chemistry of the capsules, allowed “caged” LC
droplets to be attached to single cells and used to report the presence of toxic
substances in the local environment of the cells.
Technical
Description: The Wisconsin MRSEC has recently discovered a
method to encapsulate or “cage” micrometer-sized liquid crystal (LC) droplets
inside microcapsules prepared by ‘reactive/covalent’ assembly of
azlactone-functionalized polymer multilayers. When exposed to
interfacially active molecules, the caged LC droplets can be programmed to
increasingly wet or dewet the inner surface of the capsule, resulting in a series
of complex droplet shapes, including lenses, hemispheres, and concave
hemispheres. Concurrent with the wetting transition, the internal
configurational states of the LC were also observed to change, thus revealing
that the caging of LC droplets can be used to generated ordering and wetting
transitions not seen with free LC droplets.
The response of the LC within the capsules reflects a delicate balance
of elastic and surface anchoring energies and capillary stresses, and thus
provides new designs of responsive soft matter.
Because the LC droplets are encapsulated, they can be attached to living
mammalian cells and be used report the presence of local concentrations of
cytotoxic molecules in the local environments of single cells.
