10 research outputs found
Photothermal circular dichroism measurements of single chiral gold nanoparticles correlated with electron tomography
Chemically synthesized metal nanoparticles with morphological chiral features are known to exhibit strong circular dichroism. However, we still lack understanding of the correlation between morphological and chiroptical features of plasmonic nanoparticles. To shed light on that question, single nanoparticle experiments are required. We performed photothermal circular dichroism measurements of single chiral and achiral gold nanoparticles and correlated the chiroptical response to the 3D morphology of the same nanoparticles retrieved by electron tomography. In contrast to an ensemble measurement, we show that individual particles within the ensemble display a broad distribution of strength and handedness of circular dichroism signals. Whereas obvious structural chiral features, such as helical wrinkles, translate into chiroptical ones, nanoparticles with less obvious chiral morphological features can also display strong circular dichroism signals. Interestingly, we find that even seemingly achiral nanoparticles can display large g-factors. The origin of this circular dichroism signal is discussed in terms of plasmonics and other potentially relevant factors.Biological and Soft Matter Physic
Tip-Specific Functionalization of Gold Nanorods for Plasmonic Biosensing: Effect of Linker Chain Length
Gold
nanorods are promising platforms for label-free biosensing.
We have functionalized gold nanorods with biotin thiol linkers of
increasing chain length and evaluated their ability in the molecular
detection of streptavidin. We have found an unexpected effect of the
increase in linker length, which resulted in a substantial improvement
of the plasmon response at surface saturation. The plasmon peak shift
increased from 5 to 14 nm, i.e., more than twice the response, between
the short and long biotin linkers. This effect is observed only for
site-selective tip functionalization, whereas for a full biotin coating
there is no improvement observed with the linker length. The improved
plasmon response for tip functionalization is attributed to low biotin
coverage but is directed to the most sensitive regions, which, combined
with a longer chain linker, reduces the steric hindrance for streptavidin
binding on the rod’s surface. The model sensors were further
characterized by measuring their dose–response curves and binding
kinetic assays. Simulations of the discrete dipole approximation give
theoretical plasmon shifts that compare well with the experimental
ones for the long linker but not with those of the short linker, thus
suggesting that steric hindrance affects the latter. Our results highlight
the importance of specifically functionalizing the plasmonic hot spots
in nanoparticle sensors with the adequate density of receptors in
order to maximize their response