Impact of Optical Cavity on Refractive Index Sensitivity of Gold Nanohole Arrays.

Refractive index sensing based on surface plasmon resonance (SPR) is a highly efficient label-free technique for biomolecular detection. The performance of this method is defined by the dielectric properties of a sensing layer and its structure. Nanohole arrays in thin metal films provide good refractive index sensitivity but often suffer from a large resonance linewidth, which limits their broad practical application in biosensorics.

Protein Mobility Measurements through Oxidative Green-to-Red Photoconversion of EGFP.

Protein dynamics plays a key role in live cell functioning, stimulating the development of new experimental techniques for studying protein transport phenomena. Here, we introduce a relaxation method that is based on the rapid formation of a nonequilibrium concentration profile of the enhanced green fluorescent protein (EGFP) across a sample by its oxidative green-to-red photoconversion. Following the blue-light irradiation of a part of a sample containing EGFP and an oxidant, the diffusion-controlled response of a system is monitored.

Efficiency of Plasmon-Induced Dual-Mode Fluorescence Enhancement upon Two-Photon Excitation.

Anisotropic noble metal nanoparticles supporting more than one localized surface plasmon resonance can be tailored for efficient dual-mode fluorescence enhancement by ensuring an adequate coupling to both absorption and emission bands of fluorophores. This approach is naturally extended to two-photon excitation fluorescence, where a molecule is excited by simultaneous nonlinear absorption of two photons. However, the relative impact of plasmon coupling to excitation and emission on the overall fluorescence enhancement can be very different in this case.

Plasmon-Enhanced Fluorescence of EGFP on Short-Range Ordered Ag Nanohole Arrays.

Fluorescence of organic molecules can be enhanced by plasmonic nanostructures through coupling to their locally amplified electromagnetic field, resulting in higher brightness and better photostability of fluorophores, which is particularly important for bioimaging applications involving fluorescent proteins as genetically encoded biomarkers. Here, we show that a hybrid bionanosystem comprised of a monolayer of Enhanced Green Fluorescent Protein (EGFP) covalently linked to optically thin Ag films with short-range ordered nanohole arrays can exhibit up to 6-fold increased brightness. The largest enhancement factor is observed for nanohole arrays with a propagating surface plasmon mode, tuned to overlap with both excitation and emission of EGFP.

Dynamic gas extraction of iodine in combination with a silver triangular nanoplate-modified paper strip for colorimetric determination of iodine and of iodine-interacting compounds.

A method is described for sensitive and selective detection of iodine by using a paper strip modified with silver triangular nanoplates (AgTNPs). It is based on the extraction of iodine from a solution into a flow of air via dynamic gas extraction and transferring it through a reactive paper modified with AgTNPs. The interaction of AgTNPs with iodine results in a color change from blue to white.

Chiral Plasmonic Biosensors.

Biosensing requires fast, selective, and highly sensitive real-time detection of biomolecules using efficient simple-to-use techniques. Due to a unique capability to focus light at nanoscale, plasmonic nanostructures provide an excellent platform for label-free detection of molecular adsorption by sensing tiny changes in the local refractive index or by enhancing the light-induced processes in adjacent biomolecules. This review discusses the opportunities provided by surface plasmon resonance in probing the chirality of biomolecules as well as their conformations and orientations.

Chiral plasmonic nanocrescents: large-area fabrication and optical properties.

Large-area arrays of substrate-supported plasmonic gold crescents are fabricated by using the new colloidal lithography technique, which is based on an in situ-deposited silica resistance layer. The method provides the means to control the particles' asymmetry just by changing the mutual deposition angle of gold and silica. Asymmetric crescent structures exhibit a pronounced circular dichroism in near-infrared region, with the chiral asymmetry factor reaching 0.

Dynamic protein coronas revealed as a modulator of silver nanoparticle sulphidation in vitro.

Proteins adsorbing at nanoparticles have been proposed as critical toxicity mediators and are included in ongoing efforts to develop predictive tools for safety assessment. Strongly attached proteins can be isolated, identified and correlated to changes in nanoparticle state, cellular association or toxicity. Weakly attached, rapidly exchanging proteins are also present at nanoparticles, but are difficult to isolate and have hardly been examined.

Multifunctional biosensor based on localized surface plasmon resonance for monitoring small molecule-protein interaction.

We report an optical sensor based on localized surface plasmon resonance (LSPR) to study small-molecule protein interaction combining high sensitivity refractive index sensing for quantitative binding information and subsequent conformation-sensitive plasmon-activated circular dichroism spectroscopy. The interaction of α-amylase and a small-size molecule (PGG, pentagalloyl glucose) was log concentration-dependent from 0.5 to 154 μM.

Spatial mapping and quantification of soft and hard protein coronas at silver nanocubes.

Protein coronas around silver nanocubes were quantified in serum-containing media using localized surface plasmon resonances. Both soft and hard coronas showed exposure-time and concentration-dependent changes in protein surface density with time-dependent hardening. We observed spatially dependent kinetics of the corona-formation at cube edges/corners versus facets at short incubation times, where the polymer stabilization agent delayed corona hardening.

Onset of bonding plasmon hybridization preceded by gap modes in dielectric splitting of metal disks.

Dielectric splitting of nanoscale disks was studied experimentally and via finite-difference time-domain (FDTD) simulations through systematic introduction of multiple ultrathin dielectric layers. Tunable, hybridized dark bonding modes were seen with first-order gap modes preceding the appearance of bonding dipole-dipole disk modes. The observed bright dipolar mode did not show the energy shift expected from plasmon hybridization but activated dark higher order gap modes.

Enhanced refractive index sensitivity of elevated short-range ordered nanohole arrays in optically thin plasmonic Au films.

A simple development of the colloidal lithography technique is demonstrated for fabrication of perforated plasmonic metal films elevated above the substrate surface. The bulk refractive index sensitivity of short-range ordered nanohole arrays in 20 nm thick Au films exhibits an increase of up to 37% due to reduction of substrate effect caused by lifting with a 40 nm silica layer. Analysis of the local electric field distribution suggests that the sensitivity increase is due to revealing of the enhanced field near the holes.

From rings to crescents: a novel fabrication technique uncovers the transition details.

A novel fabrication route is reported for the generation of substrate-supported symmetric and asymmetric metal nanostructures. We combine a colloidal template and angled evaporation to deposit in situ mask materials for subsequent lithographic pattern transfer. The technique is demonstrated for the fabrication of concentric and nonconcentric gold rings and crescents.

HArF in solid argon revisited: transition from unstable to stable configuration.

The thermal conversion of HArF configurations in solid argon has been investigated both experimentally and theoretically. The matrix isolation experiments have been concentrated on temperatures 25-27 K, promoting the transition from the unstable to stable HArF configuration. The combined quantum mechanical-molecular mechanical and temperature-accelerated dynamics approach has been developed to study the real-time evolution of HArF trapped in different matrix-site morphologies.