5 research outputs found
Stabilization of Metal Nanoparticle Films on Glass Surfaces Using Ultrathin Silica Coating
Metal nanoparticle (NP) films, prepared
by adsorption of NPs from
a colloidal solution onto a preconditioned solid substrate, usually
form well-dispersed random NP monolayers on the surface. For certain
metals (e.g., Au, Ag, Cu), the NP films display a characteristic localized
surface plasmon resonance (LSPR) extinction band, conveniently measured
using transmission or reflection ultraviolet–visible light
(UV-vis) spectroscopy. The surface plasmon band wavelength, intensity,
and shape are affected by (among other parameters) the NP spatial
distribution on the surface and the effective refractive index (RI)
of the surrounding medium. A major concern in the formation of such
NP assemblies on surfaces is a commonly observed instability, i.e.,
a strong tendency of the NPs to undergo aggregation upon removal from
the solution and drying, expressed as a drastic change in the LSPR
band. Since various imaging modes and applications require dried NP
films, preservation of the film initial (wet) morphology and optical
properties upon drying are highly desirable. The latter is achieved
in the present work by introducing a convenient and generally applicable
method for preventing NP aggregation upon drying while preserving
the original film morphology and optical response. Stabilization of
Au and Ag NP monolayers toward drying is accomplished by coating the
immobilized NPs with an ultrathin (3.0–3.5 nm) silica layer,
deposited using a sol–gel reaction performed on an intermediate
self-assembled aminosilane layer. The thin silica coating prevents
NP aggregation and maintains the initial NP film morphology and LSPR
response during several cycles of drying and immersion in water. It
is shown that the silica-coated NP films retain their properties as
effective LSPR transducers
Direct Observation of Aminoglycoside–RNA Binding by Localized Surface Plasmon Resonance Spectroscopy
RNA is involved in fundamental biological functions when
bacterial
pathogens replicate. Identifying and studying small molecules that
can interact with bacterial RNA and interrupt cellular activities
is a promising path for drug design. Aminoglycoside (AMG) antibiotics,
prominent natural products that recognize RNA specifically, exert
their biological functions by binding to prokaryotic ribosomal RNA
and interfering with protein translation, ultimately resulting in
bacterial cell death. The decoding site, a small internal loop within
the 16S rRNA, is the molecular target for the AMG antibiotics. The
specificity of neomycin B, a highly potent AMG antibiotic, to the
ribosomal decoding RNA site, was previously studied by observing AMG–RNA
complexes in solution. Here, we study this interaction using localized
surface plasmon resonance (LSPR) transducers comprising gold island
films prepared by evaporation on glass and annealing. Small molecule
AMG receptors were immobilized on the Au islands via polyethylene
glycol (PEG)-thiol linkers, and the interaction with target RNA in
solution was studied by monitoring the change in the LSPR optical
response upon binding. The results show high-affinity binding of neomycin
to 27-nucleotide model A-site RNA sequence in the nanomolar range,
while no specific binding is observed for synthetic RNA oligomers
(e.g., poly-U). The impact of specific base substitutions in the A-site
RNA constructs on binding affinity and selectivity is determined quantitatively.
It is concluded that LSPR is a powerful tool for providing molecular
insight into small molecule–RNA interactions and for the design
and screening of selective antimicrobial drugs