Biochemical-chemical sensing with plasmonic sensors is widely performed by tracking the responses of surface plasmonic resonance peaks to changes in the medium. Interestingly, consistent sensitivity ...and resolution improvements have been demonstrated for gold nanoparticles by analyzing other spectral features, such as spectral inflection points or peak curvatures. Nevertheless, such studies were only conducted on planar platforms and were restricted to gold nanoparticles. In this work, such methodologies are explored and expanded to plasmonic optical fibers. Thus, we study-experimentally and theoretically-the optical responses of optical fiber-doped gold or silver nanospheres and optical fibers coated with continuous gold or silver thin films. Both experimental and numerical results are analyzed with differentiation methods, using total variation regularization to effectively minimize noise amplification propagation. Consistent resolution improvements of up to 2.2× for both types of plasmonic fibers are found, demonstrating that deploying such analysis with any plasmonic optical fiber sensors can lead to sensing resolution improvements.
Poly(vinylpyrrolidone) (PVP) is a polymer capable of complexing and stabilizing Ag and Au nanoparticles formed through the reduction of Ag+ or AuCl4 - ions with N,N-dimethylformamide. The reduction ...can be efficiently performed both at reflux and under microwave irradiation, but each of these methods leads to different nanoparticle morphology and colloid stability. The use of microwave irradiation provides an extra degree of control of the reduction process. The use of PVP with different polymer chain lengths leads to particles with similar sizes though with a different degree of stability. The colloids are also stable in ethanol for months, but only marginally stable in water.
SERS permits identifying the nature of molecules in extremely low concentrations, but it is hindered by poor enhancement or low reproducibility. We demonstrate controllable ∼1010 signal amplification ...reaching the zeptomol detection limit for a nonresonant molecule by sandwiching the analyte between the tips of star-shaped gold nanoparticles and a planar gold surface using a simple synthetic procedure. This unprecedented control over light-intensity amplification opens a new avenue toward high-yield, fully reproducible, SERS-based, zeptomol detection and holds promise for nonlinear optics applications at the single-particle level.
Single‐crystalline Cu nanoplates with a prominent in‐plane dipole surface plasmon band are fabricated through reduction of copper salt with hydrazine using PVP as stabilizer and no need for inert ...atmosphere. Due to the lower free‐electron character of copper, the interband transitions overlap, and therefore damp, the out‐of‐plane dipole plasmon resonance (see image).
We introduce a new family of spiked particles resulting from the growth of high aspect ratio gold nanorods. Upon spike growth, elongated beads are obtained with sizes above 300 nm. Interestingly, and ...in contrast to smooth particles of the same size, these spiked‐particles are not only able to sustain localized surface plasmon resonances and consequently enhance Raman signals, but are also big enough to be recognized by standard confocal optical microscopy. These spiked beads have been engineered into thin films to test their surface‐enhanced Raman scattering (SERS) enhancing efficiency as a function of the particle density. Such films provide a high level of portability and easiness of use for “in‐field” optical ultrasensitive analysis.
One to enhance them all: Spiked gold beads are efficient optical enhancers for single‐particle SERS ultradetection (see picture), due to the localization of high electric fields at the apex of the tips and the antenna effect displayed by the core.
The enzymatic activity of human carbonic anhydrase II (HCAII) was studied in the presence of nanoparticles of different nature and charge. Negatively charged nanoparticles inhibit HCAII whereas no ...effect is seen for positively charged particles. The kinetic effects were correlated with the strength of binding of the enzyme to the particle surface as measured by ITC and adsorption assays. Moreover, conformational changes upon adsorption were observed by circular dichroism. The main initial driving force for the adsorption of HCAII to nanoparticles is of electrostatic nature whereas the hydrophobic effect is not strong enough to drive the initial binding. This is corroborated by the fact that HCAII do not adsorb on positively charged hydrophobic polystyrene nanoparticles. Furthermore, the dehydration of the particle and protein surface seems to play an important role in the inactivation of HCAII by carboxyl-modified polystyrene nanoparticles. On the other hand, the inactivation by unmodified polystyrene nanoparticles is mainly driven by intramolecular interactions established between the protein and the nanoparticle surface upon conformational changes in the protein.
Microbes produce bioactive chemical compounds to influence the physiology and growth of their neighbors, and our understanding of their biological activities may be enhanced by our ability to ...visualize such molecules in vivo. We demonstrate here the application of surface-enhanced Raman scattering spectroscopy for simultaneous detection of quorum-sensing-regulated pyocyanin and violacein, produced respectively by Pseudomonas aeruginosa and Chromobacterium violaceum bacterial colonies, grown as a coculture on agar-based plasmonic substrates. Our plasmonic approach allowed us to visualize the expression and spatial distribution of the microbial metabolites in the coculture taking place as a result of interspecies chemical interactions. By combining surface-enhanced Raman scattering spectroscopy with analysis of gene expression we provide insight into the chemical interplay occurring between the interacting bacterial species. This highly sensitive, cost-effective, and easy to implement approach allows spatiotemporal imaging of cellular metabolites in live microbial colonies grown on agar with no need for sample preparation, thereby providing a powerful tool for the analysis of microbial chemotypes.
Changing faces: The shape of gold nanorods can be finely tuned by controlled growth under sonication in DMF in the presence of poly(vinylpyrrolidone). Reshaping involves the formation of rods with ...sharp tips and strongly faceted lateral faces, and ultimately leads to perfect, single‐crystal octahedrons (see images). Mechanistic considerations indicate a shape‐inducing effect of the polymer through different binding interactions for the different faces.
A novel 3D boundary element method that proves extremely efficient for modeling the optical response of metal nanoparticles with arbitrary shapes is presented. The method is computationally more ...efficient than other methods currently used, and should therefore be of interest for modeling of complex nanostructures.
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