posted on 2024-02-06, 22:06authored byOscar
H. Piñeres-Quiñones, Maria K. Oñate-Socarras, Fengrui Wang, David M. Lynn, Claribel Acevedo-Vélez
We
report emulsions of thermotropic liquid crystals (LCs)
in water
that are stabilized using amphiphilic gold nanoparticles (AuNPs) and
retain their ability to respond to aqueous analytes for extended periods
(e.g., up to 1 year after preparation). These LC emulsions exhibit
exceptional colloidal stability that results from the adsorption of
AuNPs that are functionalized with thiol-terminated poly(ethylene
glycol) (PEG-thiol) and hexadecanethiol (C16-thiol) to
LC droplet interfaces. These stabilized LC emulsions respond to the
presence of model anionic (SDS), cationic (C12TAB), and
nonionic (C12E4) surfactants in the surrounding
aqueous media, as evidenced by ordering transitions in the LC droplets
that can be readily observed using polarized light microscopy. Our
results reveal significant differences in the sensitivity of the stabilized
LC droplets toward each of these analytes. In particular, these stabilized
droplets can detect the cationic C12TAB at concentrations
that are lower than those required for bare LC droplets under similar
experimental conditions (0.5 and 2 mM, respectively). These results
demonstrate an enhanced sensitivity of the LC toward C12TAB when the PEG/C16-thiol-coated AuNPs are adsorbed at
LC droplet interfaces. In contrast, the concentrations of SDS required
to observe optical transformations in the stabilized LC droplets are
higher than those required for the bare LC droplets, suggesting that
the presence of the PEG/C16-thiol AuNPs reduces the sensitivity
of the LC toward this analyte. When combined, our results show that
this Pickering stabilization approach using amphiphilic AuNPs as stabilizing
agents for LC-in-water emulsions provides a promising platform for
developing LC droplet-based optical sensors with long-term colloidal
stability as well as opportunities to tune the sensitivity and selectivity
of the response to target aqueous analytes.