Tailored Colloidal Nanostars for Surface-Enhanced
Raman Spectroscopy: Optimization of Formulation Components and Study
of the Stabilizer–Nanoparticle Interactions
posted on 2022-01-25, 20:13authored byChiara Deriu, Asier Bracho, Bruce McCord
While the effects of the morphology
and composition of plasmonic
substrates in Surface-Enhanced Raman Spectroscopy (SERS) are widely
studied, surface chemistry and, more specifically, the role of preadsorbed
species on colloidal substrates (i.e., stabilizers
and synthesis byproducts) are typically less explored. In this paper,
a surfactant-free synthesis of sparingly capped bimetallic colloidal
AuAg nanostars was selected as a basis to (1) examine the effect of
varying stabilizers and (2) systematically assess the impact of the
resulting surface environment on SERS intensity. The latter entailed
the characterization of the colloidal formulations in terms of optical
reproducibility, suitability for analytical applications, long-term
colloidal stability, and SERS performance. Emphasis was given to the
elucidation of the stabilizer–metal interactions, which were
studied by electrophoretic light scattering and infrared spectroscopy.
It was found that the capping process is the result of chemisorption
to an essentially neutral alloy and that the capping environment has
effects on the SERS response that can overtop those caused by nanoparticle
morphology. The model stabilizer, citrate, was found to weakly chemisorb
(−4.36 ± 0.08 and −4.58 ± 0.05 kJ/mol at 10
and 20 °C, respectively) to the bimetallic surface in a positively
cooperative fashion (nHill > 1) via
the
unidentate mode.