We
report colloidally stable emulsions of thermotropic liquid crystals
(LCs) that can detect the presence of amphiphilic analytes in aqueous
environments. Our approach makes use of a Pickering stabilization
strategy consisting of surfactant–nanoparticle complexes (SiO2/C
n
TAB, n = 8,
12, 16) that adsorb to aqueous/LC droplet interfaces. This strategy
can stabilize LC emulsions against coalescence for at least 3 months.
These stabilized LC emulsions also retain the ability to respond to
the presence of model anionic, cationic, and nonionic amphiphiles
(e.g., SDS, C12TAB, C12E4) in aqueous
solutions by undergoing “bipolar-to-radial” changes
in LC droplet configurations that can be readily observed and quantified
using polarized light microscopy. Our results reveal these ordering
transitions to depend upon the length of the hydrocarbon tail of the
C
n
TAB surfactant used to form the stabilizing
complexes. In general, increasing C
n
TAB
surfactant tail length leads to droplets that respond at lower analyte
concentrations, demonstrating that this Pickering stabilization strategy
can be used to tune the sensitivities of the stabilized LC droplets.
Finally, we demonstrate that these colloidally stable LC droplets
can report the presence of rhamnolipid, a biosurfactant produced by
the bacterial pathogen Pseudomonas aeruginosa. Overall,
our results demonstrate that this Pickering stabilization strategy
provides a useful tool for the design of LC droplet-based sensors
with substantially improved colloidal stability and new strategies
to tune their sensitivities. These advances could increase the potential
practical utility of these responsive soft materials as platforms
for the detection and reporting of chemical and biological analytes.