18 research outputs found
SERS Primers and Their Mode of Action for Pathogen DNA Detection
SERS primers have been used to directly detect specific
PCR products
utilizing the difference in adsorption of single-stranded and double-stranded
DNA onto nanoparticle surfaces. Herein, seven parameters important
for improved positive SERS assays for real applications were investigated.
First, we applied a model system for optimization experiments, followed
by a PCR assay to detect pathogen DNA, and then the introduction of
a new assay that utilizes the 5â˛â3Ⲡexonuclease
activity of <i>Taq</i> DNA polymerase to partly digest the
SERS probe, generating dye-labeled single-stranded DNA increasing
the SERS signals for detection of pathogen DNA. Applying the model
system, it was found that uni-molecular SERS primers perform better
than bi-molecular SERS primers. However, within the PCR assays, it
was found that uni- and bi-molecular SERS primers performed very similarly,
and the most reproducible results were obtained using the 5â˛â3â˛
exonuclease digestion assay. These SERS-based assays offer new routes
over conventional fluorescence-based techniques without compromising
sensitivity or selectivity
Design Consideration for Surface-Enhanced (Resonance) Raman Scattering Nanotag Cores
Surface-enhanced (resonance) Raman spectroscopy (SEÂ(R)ÂRS)
holds
great promise for the in vivo detection of multiple disease markers.
Nanotags consisting of a metallic nanoparticle decorated with reporter
molecules encapsulated in either an inert or biofunctionalized shell,
for inactive or active targeting, have been developed. To improve
the tissue depth from which the signal can be detected, it is preferable
to operate with excitation in the near-infrared wavelengths; however,
this reduces the inherent Raman signal intensity. The signal strength
can be reestablished by matching the absorbance of the nanoparticle
with the laser excitation. However, nanoparticles must get physically
larger to support absorbances in the near-infrared region, which can
have an adverse affect on cellular uptake. In this paper we compare
the use of silver nanoparticles with plasmon absorbances at longer
wavelengths with clusters (2â4 nanoparticles) formed from much
smaller nanoparticles which support so-called âhot spotsâ.
We find that the small clusters outperform the resonant single nanoparticles
with respect to the observed SEÂ(R)ÂRS signal. It has also previously
been shown in the literature that small nanoparticles are more readily
taken up into cells than larger nanoparticles. This knowledge combined
with the results reported here highlight an important design consideration
in that new SEÂ(R)ÂRS active nanotags should be made from coupled small
dimensional nanoparticles rather than large single nanoparticles that
support absorbances in the near-infrared region
Confocal SERS Mapping of Glycan Expression for the Identification of Cancerous Cells
Lectin-functionalized
silver nanoparticles have been successfully
designed for use as molecular imaging agents to investigate carbohydrateâlectin
interactions at the surface of mammalian cells, using surface-enhanced
Raman scattering (SERS). Carbohydrate-lectin interactions are key
to many cellular processes and are responsible for controlling an
array of cellular interactions. In this study, lectin-functionalized
silver nanoparticles were used to detect the expression of carbohydrate
species at the cellular interface. The carbohydrateâlectin
interactions were demonstrated using three different lectin species
for three distinct cell types. Due to the known difference between
the expressions of glycans in cancerous versus noncancerous cells
of the same origin, this approach has been expanded to study both
cancerous and noncancerous prostate cells. This has been achieved
via confocal SERS mapping of the expression of the key glycan, sialic
acid, on the surface of each of these cell types. In achieving such
discrimination, a novel method has been created by which glycan expression
can be reproducibly monitored. Comparative studies were performed
using both fluorescence and SERS. SERS provided an increased discrimination
over fluorescence when analyzing cell subsets to discriminate between
cancerous and noncancerous cells. The success of this method means
that it could be used to complement the current gold standard histopathological
techniques
Cisplatin-Tethered Gold Nanoparticles That Exhibit Enhanced Reproducibility, Drug Loading, and Stability: a Step Closer to Pharmaceutical Approval?
Gold nanoparticles (AuNPs) can be used as delivery vehicles
for
platinum anticancer drugs, improving their targeting and uptake into
cells. Here, we examine the appropriateness of different-sized AuNPs
as components of platinum-based drug-delivery systems, investigating
their controlled synthesis, reproducibility, consistency of drug loading,
and stability. The active component of cisplatin was tethered to 25,
55, and 90 nm AuNPs, with the nanoparticles being almost spherical
in nature and demonstrating good batch-to-batch reproducibility (24.37
Âą 0.62, 55.2 Âą 1.75, and 89.1 Âą 2.32 nm). The size
distribution of 25 nm AuNPs has been significantly improved, compared
with a previous method that produces polydispersed nanoparticles.
Attachment of platinum to the AuNP surface through a polyÂ(ethylene
glycol) (PEG) linker exhibits an increase in the drug loading with
increasing particle size: 25 nm (815 Âą 106 drug molecules per
AuNP), 55 nm (14216 Âą 880), and 90 nm (54487 Âą 15996). The
stability of the naked, PEGylated, and platinum-conjugated nanoparticles
has been examined over time under various conditions. When stored
at 4 °C, there is minimal variation in the diameter for all three
AuNP sizes; variation after 28 days for the 25 nm AuNPs was 2.4%;
55 nm, 3.3%; and 90 nm, 3.6%. The 25 nm AuNPs also demonstrate minimal
changes in UVâvisible absorbance over the same time period
Dynamic Imaging Analysis of SERS-Active Nanoparticle Clusters in Suspension
A novel wide-field approach for the real-time Surface Enhanced Raman Scattering (SERS) imaging of multiple silver nanoparticle clusters suspended in solution is described. This method enables direct correlation of the SERS activity of a single nanoparticle aggregate and its size through measurement of the cluster diffusion coefficient and can also be performed in a high-throughput basis. As a first demonstration, we investigate the salt-induced aggregation of silver nanoparticles in the presence of a reporter tag molecule, which has a high affinity for the nanoparticle surface. In addition to tracking individual particles, direct comparison of Rayleigh and SERS videos of the same colloid solution enabled measurement of the fraction of individual clusters that are SERS active and the dependence of this value on the relative concentration of the tag molecule. Furthermore, given the ability to also rapidly profile any nonuniformity in particle size distributions, we expect this approach will not only provide a new tool for the fundamental understanding of SERS but also significantly contribute to the development of an array of emerging nanoparticle-enhanced biomolecule and imaging detection platforms
Plasmonic and Photothermal Properties of Silica-Capped Gold Nanoparticle Aggregates
Owing to their biocompatibility,
gold nanoparticles have many applications
in healthcare, notably for targeted drug delivery and the photothermal
therapy of tumors. The addition of a silica shell to the nanoparticles
can help to minimize the aggregation of the nanoparticles upon exposure
to harsh environments and protect any Raman reporters adsorbed onto
the metal surface. Here, we report the effects of the addition of
a silica shell on the photothermal properties of a series of gold
nanostructures, including gold nanoparticle aggregates. The presence
of a Raman reporter at the surface of the gold nanoparticles also
allows the structures to be evaluated by surface-enhanced Raman scattering
(SERS). In this work, we explore the relationship between the degree
of aggregation and the position and the extinction of the near-infrared
plasmon on the observed SERS intensity and in the increase in bulk
temperature upon near-infrared excitation. By tailoring the concentration
of the silane and the thickness of the silica shell, it is possible
to improve the photothermal heating capabilities of the structures
without sacrificing the SERS intensity or changing the optical properties
of the gold nanoparticle aggregates
Directed Assembly of DNA-Functionalized Gold Nanoparticles Using PyrroleâImidazole Polyamides
Traditional methods for the construction of nanoparticle
arrays
and lattices exploit WatsonâCrick base pairing of single-stranded
DNA sequences as a proxy for self-assembly. Although this approach
has been utilized in a variety of applications in nanoassembly, diagnostics,
and biomedicine, the diversity of this recognition lexicon could be
considerably increased by developing strategies that recognize the
base-pairing landscape of double-stranded DNA (dsDNA) sequences. Herein
we describe the first report of programmed gold nanoparticle (GNP)
aggregation directed by the recognition of dsDNA sequences using pyrroleâimidazole
polyamideâGNP (PAâGNP) conjugates. We demonstrate the
reversibility and selectivity of this strategy for forming GNP aggregates
in the presence of fully matched dsDNA sequences relative to dsDNA
sequences containing one- and two-base-pair mismatches
Supporting Information from Sensitive SERS nanotags for use with a hand-held 1064â nm Raman spectrometer
General experimental details for the synthesis and characterisation of dyes 1-17 and HGNs; schematic detailing experimental setup, figures of extinction spectra for HGNs and selected chalcogenopyrylium dyes; chemical structures for dyes 1-17 and commercial reporters; SERS spectra and LOD plots for dye/HGN nanotags plus commercial reporter/HGN nanotags with 1064 nm excitation
The Use of Ni/Sb-SnO2-based Membrane Electrode Assembly for Electrochemical Generation of Ozone and the Decolourisation of Reactive Blue 50 Dye Solutions
Surface enhanced Raman scattering (SERS) âhot spotsâ are the regions where the electromagnetic field is significantly enhanced, resulting in much greater SERS activity than other areas. Therefore, the engineering and characterization of âhot spotsâ have attracted much attention. Herein, we have synthesized nanoworms formed by connecting hollow gold nanospheres and investigated their composition as well as their SERS properties, including their potential for simultaneous analysis of multiple species. The three-dimensional nanostructures that led to different SERS activities were investigated using correlated optical/SERS and SEM imaging. Gold nanoworms with hollow nanosphere segments and partial tube formation were confirmed. All highly SERS-active structures were found to be three-dimensional arrays consisting of inter-/intrananoworm interactions; no individual nanospheres were found to give significant SERS signal under the experimental conditions. The major SERS contribution was found to be the electromagnetic coupling effect within the three-dimensional arrays and the localized surface plasmon resonance of the nanostructure was found to have a minimal effect. This study gives insight into the basis of enhancement for these nanoworm structures and adds to the growing body of evidence in relation to nanostructures and surface enhancement of Raman scattering
Optoplasmonic Effects in Highly Curved Surfaces for Catalysis, Photothermal Heating, and SERS
Surface curvature can be used to focus light and alter
optical
processes. Here, we show that curved surfaces (spheres, cylinders,
and cones) with a radius of around 5 Îźm lead to maximal optoplasmonic
properties including surface-enhanced Raman scattering (SERS), photocatalysis,
and photothermal processes. Glass microspheres, microfibers, pulled
fibers, and control flat substrates were functionalized with well-dispersed
and dense arrays of 45 nm Au NP using polystyrene-block-poly-4-vinylpyridine (PS-b-P4VP) and chemically
modified with 4-mercaptobenzoic acid (4-MBA, SERS reporter), 4-nitrobenzenethiol
(4-NBT, reactive to plasmonic catalysis), or 4-fluorophenyl isocyanide
(FPIC, photothermal reporter). The various curved substrates enhanced
the plasmonic properties by focusing the light in a photonic nanojet
and providing a directional antenna to increase the collection efficacy
of SERS photons. The optoplasmonic effects led to an increase of up
to 1 order of magnitude of the SERS response, up to 5 times the photocatalytic
conversion of 4-NBT to 4,4â˛-dimercaptoazobenzene when the diameter
of the curved surfaces was about 5 Îźm and a small increase in
photothermal effects. Taken together, the results provide evidence
that curvature enhances plasmonic properties and that its effect is
maximal for spherical objects around a few micrometers in diameter,
in agreement with a theoretical framework based on geometrical optics.
These enhanced plasmonic effects and the stationary-phase-like plasmonic
substrates pave the way to the next generation of sensors, plasmonic
photocatalysts, and photothermal devices