Metallic film optimization in a surface plasmon resonance biosensor by the extended Rouard method

Performance of Surface Plasmon Resonance Sensors Using Copper/Copper Oxide Films: Influence of Thicknesses and Optical Properties

Surface plasmon resonance sensors (SPR) using copper for sensitive parts are a competitive alternative to gold and silver. Copper oxide is a semiconductor and has a non-toxic nature. The unavoidable presence of copper oxide may be of interest as it is non-toxic, but it modifies the condition of resonance and the performance of the sensor. Therefore, the characterization of the optical properties of copper and copper oxide thin films is of interest. We propose a method to recover both the thicknesses and optical properties of copper and copper oxide from absorbance curves over the (0.9;3.5) eV range, and we use these results to numerically investigate the surface plasmon resonance of copper/copper oxide thin films. Samples of initial copper thicknesses 10, 30 and 50 nm, after nine successive oxidations, are systematically studied to simulate the signal of a Surface Plasmon Resonance setup. The results obtained from the resolution of the inverse problem of absorbance are used to discuss the performance of a copper-oxide sensor and, therefore, to evaluate the optimal thicknesses.

Ultrasensitive biosensors based on waveguide-coupled long-range surface plasmon resonance (WC-LRSPR) for enhanced fluorescence spectroscopy

We investigated the coupling phenomenon between plasmonic resonance and waveguide modes through theoretical and experimental parametric analyses on the bimetallic waveguide-coupled long-range surface plasmon resonance (Bi-WCLRSPR) structure.

Point-of-Care Surface Plasmon Resonance Biosensor for Stroke Biomarkers NT-proBNP and S100β Using a Functionalized Gold Chip with Specific Antibody

Surface-plasmon-resonance (SPR) is a quantum-electromagnetic phenomenon arising from the interaction of light with free electrons at a metal-dielectric interface. At a specific angle/wavelength of light, the photon's energy is transferred to excite the oscillation of the free electrons on the surface. A change in the refractive-index (RI) may occur, which is influenced by the analyte concentration in the medium in close contact with the metal surface. SPR has been widely used for the detection of gaseous, liquid, or solid samples. In this study, a functionalized specific SPR chip was designed and used in a novel point-of-care SPR module (PhotonicSys SPR H5) for the detection of the stroke biomarkers NT-proBNP and S100β. These biomarkers have proven to be good for stroke diagnosis, with sensitivity and specificity of >85%. Specific detection was done by binding a biomolecular-recognizing antibody onto the Au SPR-chip. Detection was tested in water and plasma samples. NT-proBNP and S100β were detected in a range of concentrations for stroke, from 0.1 ng/mL to 10 ng/mL. The RI of the blank plasma samples was 1.362412, and the lowest concentration tested for both biomarkers showed a prominent shift in the RI signal (0.25 ng/mL NT-proBNP (1.364215) and S100β (1.364024)). The sensor demonstrated a clinically relevant limit-of-detection of less than ng/mL.

Phase-shifted polarimetric surface plasmon resonance sensor using a liquid crystal retarder and a diverging beam

A simple phase-shifted polarimetric scheme to extract light polarization changes induced by the sample in surface plasmon resonance (SPR) sensors is presented. The proposed method is based on the conventional Kretschmann-Raether configuration in the angular diverging beam mode using a single wavelength and a variable liquid crystal retarder. An experimental demonstration was performed using different aqueous solutions of ethylene glycol showing a sensitivity of 118.7 deg/refractive-index-unit (RIU) and a detection limit of 1.03×10^-7  RIU.

Comparative study between polarimetric and intensity-based surface plasmon resonance sensors in the spectral mode

There is a debate on whether phase measurement in surface plasmon resonance (SPR) sensors give better resolution than intensity measurement. In this work, we show that each one of the modes can give better resolution depending on the metal layer thickness chosen, as well as the available noise levels in the system. We propose a three point polarimetric approach to extract the ellipsometric parameters and phase information in the spectral mode. It is shown that the polarimetric measurement at its optimal thickness range gives up to seven-fold higher resolution than the intensity, especially at noise levels of off the shelf spectrometers. When noise levels are very low, the resolution in the two modes becomes nearly equal. The same is true when considering the whole SPR curve rather than single point detection. However, it is clearly shown both experimentally and theoretically that the polarimetric measurements at their optimal range give much better resolution than the intensity.

Theoretical design of a surface plasmon resonance sensor with high sensitivity and high resolution based on graphene–WS2 hybrid nanostructures and Au–Ag bimetallic film

We proposed a high sensitivity and a high resolution surface plasmon resonance sensor composed of graphene–WS₂ hybrid nanostructure and Au–Ag bimetallic-layers film.

Detection of Intermolecular Interactions Based on Surface Plasmon Resonance Registration

Methods for registration of intermolecular interactions based on the phenomenon of surface plasmon resonance (SPR) have become one of the most efficient tools to solve fundamental and applied problems of analytical biochemistry. Nevertheless, capabilities of these methods are often insufficient to detect low concentrations of analytes or to screen large numbers of objects. That is why considerable efforts are directed at enhancing the sensitivity and efficiency of SPR-based measurements. This review describes the basic principles of the detection of intermolecular interactions using this method, provides a comparison of various types of SPR detectors, and classifies modern approaches to enhance sensitivity and efficiency of measurements.

Optical properties of ultrafine line and space polymeric nanogratings coated with metal and metal-dielectric-metal thin films

Noble metal and metal-dielectric-metal ultrathin films were deposited on the surfaces of ultrafine polymeric nanogratings, which were fabricated using nanoimprint lithography. Experimental results showed dramatic differences of the surface morphologies for single metal and triple metal-dielectric-metal films deposited on flat and corrugated polymeric surfaces. The effect of the surface morphology on the optical properties was hence investigated and analyzed under linearly polarized light. The surface plasmon resonances of single metal and triple metal-dielectric-metal films deposited on polymeric nanograting surfaces were also characterized based on the Kretschmann prism-coupling method. The single metal and triple metal-dielectric-metal films deposited on polymeric nanograting surfaces are important for the study of photon-plasmon interactions (i.e. couplings and conversions) at the interfaces between a nanograting and metal films.

Biochip data normalization using multifunctional probes

Using a biochip with stable probe functionalization and a detection system capable of real time measurements, it is demonstrated that acquired probe-target interaction data are more reproducible in time--on a given probe spot using sequential target runs--than in space, using many probe spot replicates on the biochip in one single parallel target run. To increase the biochip data precision, a normalization method that quantifies and corrects the surface inhomogeneity without the use of complex data post-processing has been developed. This simple and effective method is based on adding a common reactive group to all probes and quantifying the biochip response to a calibration target, thus quantifying the spatial heterogeneity in the biosensor responsiveness. The usefulness of such methodology, which can be easily generalized, is demonstrated in the model case of DNA:DNA interactions, using a surface plasmon resonance imaging system as the dynamical reader. The biochips are based on streptavidin biochemically functionalized gold films onto which biotinylated ssDNA probe sequences, related to cystic fibrosis genotyping, are spotted. This normalization method provides high gain in data precision and allows, in this example, unambiguous genotyping of SNP, including discrimination of the heterozygote case from the two homozygote cases.

Adaptive Non-Uniform Particle Swarm Application to Plasmonic Design

The metaheuristic approach has become an important tool for the optimization of design in engineering. In that way, its application to the development of the plasmonic based biosensor is apparent. Plasmonics represents a rapidly expanding interdisciplinary field with numerous transducers for physical, biological and medicine applications. Specific problems are related to this domain. The plasmonic structures design depends on a large number of parameters. Second, the way of their fabrication is complex and industrial aspects are in their infancy. In this study, the authors propose a non-uniform adapted Particle Swarm Optimization (PSO) for rapid resolution of plasmonic problem. The method is tested and compared to the standard PSO, the meta-PSO (Veenhuis, 2006) and the ANUHEM (Barchiesi, 2009).These approaches are applied to the specific problem of the optimization of Surface Plasmon Resonance (SPR) Biosensors design. Results show great efficiency of the introduced method.

Surface plasmon resonance on gold and silver films coated with thin layers of amorphous silicon-carbon alloys

The paper reports on a novel surface plasmon resonance (SPR) substrate architecture based on the coating of a gold (Au) or silver (Ag) substrate with 5 nm thin amorphous silicon-carbon alloy films. Ag/a-Si(1-x)C(x):H and Au/a-Si(1-x)C(x):H multilayers are found to provide a significant advantage in terms of sensitivity over both Ag and Au for SPR refractive index sensing. The possibility for the subsequent linking of stable organic monolayers through Si-C bonds is demonstrated. In a proof-of-principle experiment that this structure can be used for real-time biosensing experiments, amine terminated biotin was covalently linked to the acid-terminated SPR surface and the specific streptavidin-biotin interaction recorded.

Preparation and characterization of silver substrates coated with antimony-doped SnO2 thin films for surface plasmon resonance studies

This paper reports on the preparation of silver/antimony-doped tin oxide (Ag/SnO(2):Sb) hybrid interfaces using magnetron sputtering and their characterization. The influence of the Sn target composition (doping with 2 or 5% Sb) on the electrochemical and electrical characteristics of the hybrid interface was investigated using X-ray photoelectron spectroscopy (XPS), sheet resistance measurements, cyclic voltammetry, scanning tunneling microscopy (STM) and surface plasmon resonance (SPR). The best interface in terms of electrical conductivity and SPR signal is a hybrid interface with a 8.5 +/- 0.3 nm thick SnO(2):Sb layer obtained from a Sn target with 2% Sb deposited on 38 nm thick silver film. Different strategies to link functional groups onto the Ag/SnO(2):Sb interface are also presented.

Absorption and related optical dispersion effects on the spectral response of a surface plasmon resonance sensor

Surface plasmon resonance (SPR) sensing is an optical technique that allows real time detection of small changes in the physical properties, in particular in the refractive index, of a dielectric medium near a metal film surface. One way to increase the SPR signal shift is then to incorporate a substance possessing a strong dispersive refractive index in the range of the plasmon resonance band. In this paper, we investigate the impact of materials possessing a strong dispersive index integrated to the dielectric medium on the SPR reflectivity profile. We present theoretical results based on chromophore absorption spectra and on their associated refractive index obtained from the Lorentz approach and Kramers-Krönig equations. As predicted by the theory, the experimental results show an enhancement of the SPR response, maximized when the chromophore absorption band coincides with the plasmon resonant wavelength. This shows that chromophores labeling can provide a potential way for SPR response enhancement.