Shift In Plasmon Resonance Wavelength Research Articles

Design and Implementation of a Dual-Region Self-Referencing Fiber-Optic Surface Plasmon Resonance Biosensor.

The need for self-referencing is extremely important in the field of biosensing. In this manuscript, we report on the study, design, and validation of a dual-region self-referencing fiber-optic surface plasmon resonance biosensor. One region is intended to measure and monitor the binding events of the biological sample under test, while the other one is designed to be used as a reference channel to compensate for external factors, such as bulk refractive index modifications and temperature oscillations, that can negatively affect the biomolecular interaction measurement. Two different configurations for the biosensor probe are presented and investigated here, both theoretically and experimentally. First, the theoretical performance of the proposed biosensor probes, in terms of surface plasmon resonance wavelength shift, was simulated using a numerical model. Afterward, they were experimentally validated in sucrose-water solutions and showed a response to refractive index and temperature changes with sensitivities up to 2000 nm/RIU and 1.559 nm/°C, respectively. Finally, an aptamer-based bioassay and a high-resolution melting assay were successfully implemented on the two proposed configurations, demonstrating the feasibility of analyzing the binding events and measuring other external signal modifications simultaneously using the same biosensor probe.

PEI-coated Prussian blue nanocubes as pH-Switchable nanozyme: Broad-pH-responsive immunoassay for illegal additive

Nanozymes are commonly used in the construction of immunosensors, yet they are generally susceptible to pH condition, which greatly hindered their practical use. To break the limitation of pH conditions, polyethyleneimine-coated Prussian blue nanocubes (PBNCs@PEI) were synthesized as the pH-switchable nanozyme, which can show peroxidase-like and catalase-like activity in acidic and alkaline condition, respectively. Besides, the modification of PEI can largely improve the catalytic activity of PBNCs. Herein, the pH-switchable catalytic property of PBNCs@PEI was used to construct the dual-mode immunosensor for the detection of illegal additive, rosiglitazone. In acidic condition, PBNCs@PEI showed excellent peroxidase-like activity, which can trigger the colorimetric reaction of Au nanostars with TMB2+/CTAB. In alkaline condition, the catalase-like activity of PBNCs@PEI prevailed, thus the decomposition of H2O2 can generate O2 to initiate the aerobic oxidation of 4-chloro-1-naphthol (4-CN), which can decrease the fluorescence intensity of 4-CN. Based on the competitive immunoassay, both the localized surface plasmon resonance wavelength shift of Au nanostars and the fluorescence intensity change of 4-CN were quantitatively related with rosiglitazone concentration, thus shedding a new light on the construction of broad-pH-responsive immunosensor. Besides, a smart device was developed to transfer the chroma value of Au nanostars into the RSG concentration, making this sensor a promising method in on-site and point-of-care detection.

Design and simulation of high sensitive cylindrical nanogear shell sensors according to localized surface plasmon resonance

Localized surface plasmon resonance wavelength depends on intrinsic and environmental factors of nanoparticles. One of the most important factors is the shape of nanoparticles. The effects of nanoparticles shape on the surface plasmon resonance wavelength shift are simulated and investigated. We have observed that the sensitivity of single cylindrical nanoshell with inner and outer radiuses of 20 and 25nm and length of 70nm is 509nm/RIU while the sensitive nature of nanogear with the same size is 603nm/RIU. It is nearly four times the sensitivity of solid spherical nanoparticles and two times the sensitivity of solid nanorods.

Plasmon Resonances in Self-Assembled Two-Dimensional Au Nanocrystal Metamolecules

We explore the evolution of plasmonic modes in two-dimensional nanocrystal oligomer "metamolecules" as the number of nanocrystals is systematically varied. Precise, hexagonally ordered Au nanocrystal oligomers with 1-31 members are assembled via capillary forces into polygonal topographic templates defined using electron-beam lithography. The visible and near-infrared scattering response of individual oligomers is measured by spatially resolved, polarized darkfield scattering spectroscopy. The response is highly sensitive to in-plane versus out-of-plane incident polarization, and we observe an exponentially saturating red shift in plasmon resonance wavelength as the number of nanocrystals per oligomer increases, in agreement with theoretical predictions. Simulations further elucidate the modes supported by the oligomers, including electric dipole and magnetic dipole resonances and their Fano interference. The single-oligomer sensitivity of our measurements also reveals the role of positional disorder in determining the wavelength and character of the plasmonic response. The progression of oligomer metamolecule structures studied here advances our understanding of fundamental plasmonic interactions in the transition regime between few-member plasmonic clusters and extended two-dimensional arrays.

Novel Plasmonic Structures Based on Gold Nanobelts

Gold nanobelts are elongated nanostructures that exhibit plasmon resonant scattering that is tunable with the cross-sectional aspect ratio. Their surfactant-directed chemical synthesis produces uniform nanobelts as well as similar, yet more complex, structures. Tapered gold nanobelts have a shift in their cross-sectional aspect ratio along their length and, therefore, a shift in plasmon resonance wavelength. The tapered nanobelts are shown to act as mesoscale plasmonic spectrometers to probe enhanced emission from nearby quantum dots. Nanobelts also form dimers, either because of bifurcation during growth or because of alignment during deposition, that run side by side with sub-10 nm gaps which create large volumes of electromagnetic enhancement for surface-enhanced Raman spectroscopy.

Size Dependence of the Plasmon Ruler Equation for Two-Dimensional Metal Nanosphere Arrays

We have utilized the discrete dipole approximation to study the localized surface plasmon resonance in infinite, periodic two-dimensional arrays of gold nanospheres with the nanospheres arranged according to the {100} face of an fcc crystal. Specifically, we have performed a systematic study of the sensitivity of both the plasmon resonance wavelength shift and extinction properties considering nanosphere diameters ranging from 20 to 100 nm, and for nanosphere gap distances ranging from 0.5 to 6 times the nanosphere diameter. In doing so, we find that the same universal decay length of the plasmon resonance wavelength shift of about 0.2 units of the nanosphere size that was previously found by Jain et al.(1) for nanoparticle dimers is also operant for two-dimensional arrays. However, we also find that the universality of the plasmon ruler is only valid for arrays with nanospheres smaller than a critical nanosphere diameter of about 70 nm, whereas for larger nanosphere diameters, a decrease in the extinctio...

Improved Description of the Plasmon Resonance Wavelength Shift in Metallic Nanoparticle Pairs

We propose to use the compressed or stretched hyperbola for an efficient description of the plasmon resonance shift as a function of the gap between proximal nanoparticles in arrays of gold pairs. This function overcomes the limitation of describing this behavior by the well-known exponential function as it accounts for the near-field coupling and the far-field radiative coupling between particles . It has the advantage of mathematical simplicity with one dimensionless additional parameter compared to a simple exponential decay. We suggest that this parameter may be the signature of the grating effects. Most importantly this function works well in a wide variety of surrounding media and for nanostructures with arbitrary shapes. We expect that this function is an efficient tool for fundamental studies as it quantifies both the near-field coupling and the grating coupling. It is also a useful tool for applied studies like bio-sensing applications, by providing an improved plasmon ruler equation. Localized surface plasmon resonances in gold pairs are investigated using finite-difference time-domain simulations.

Double-resonance plasmon and polarization effects in a SERS fiber sensor with a grid nanostructure

We presented a systematic study of surface enhanced Raman scattering (SERS) fiber sensor with a grid nanostructure. The plasmonic resonance peak is stable when measuring gas and double-resonance plasmon can be effectively excited; meanwhile local electric field can be strongly enhanced with the metal coated nanostructured fiber facet. Studies on the influence of polarization effects, the plasmon resonance wavelength shift is relatively small in our structure.