Grating-coupled Surface Plasmon Resonance Sensor Research Articles

A High-Sensitivity Bimetallic Grating-Coupled Surface Plasmon Resonance Sensor Based on Two-Dimensional Materials

Optical biosensors based on grating-coupled surface plasmon resonance (GCSPR) technology are an important research topic in the field of bio-photonics. This paper presents a high-performance and high-sensitivity nanostructured bimetallic GCSPR sensor based on two-dimensional materials. When designing the sensor, the sensitivity, full width at half peak (FWHM) and dip strength of the absorption peak (DS) were considered comprehensively, and the comprehensive evaluation parameter FOM+ is defined by making improvements on the basis of figure of merit (FOM). The performance of the sensor can be judged more comprehensively. The performance of the sensor was further improved by optimizing the structure of the sensor. An ultra-thin gold layer was added on the surface of the silver-based GCSPR sensor, which solves the problem of the easy oxidation of silver metal. We tried to coat graphene oxide two-dimensional nanomaterials on the surface of the bimetallic sensor, and the sensitivity and FOM+ of the sensor reached 350 deg/RIU and 473.23, respectively. This is a great improvement compared with the GCSPR sensor in a previous study, and it can be improved at least 74.7%. This sensor can measure a variety of biological molecules and biological cells with high sensitivity and performance by detecting the change in the refractive index of the solution to be measured.

Sensing absorptive fluids with backside illuminated grating coupled SPR sensor fabricated by nanoimprint technology

Grating coupled surface plasmon resonance (GC-SPR) sensors are widely used in analyzing gases, aqueous solutions, proteins and environmental pollutants. However, traditional GC-SPR sensors are difficult to detect absorptive fluids because the spectra of the light will be distorted after passing through the absorptive fluids. Here, we propose and experimentally demonstrate a backside illuminated GC-SPR (BIGC-SPR) sensor, where the light is incident from the transparent substrate side of the sensor chip. The grating chip is fabricated by a simple and cost-effective procedure. DVD-R disc is used as a template to imprint the grating structure onto a polydimethylsiloxane (PDMS) substrate, then a thin Au layer of 35 nm thickness is evaporated on it. By calibrating the sensor with glucose solutions, the sensitivity and refractive index resolution are measured to be 311.97 nm/RIU and 0.00043 RIU, respectively. Moreover, the BIGC-SPR sensor is demonstrated to monitor the concentration of blue engine coolant, green antirust cutting fluid and white antirust emulsified oil solutions. The designed sensor is able to detect colored or highly scattering solutions, and can be potentially used in the fields of medical diagnosis, environmental monitoring and biological protein detection.

Grating coupled SPR sensors using off the shelf compact discs and sensitivity dependence on grating period

Grating coupled surface plasmon resonance (GCSPR) sensors with wavelength modulation are widely used in many fields, but the low sensitivity holds their practical applications. Here we theoretically analyze the sensitivity limit of GCSPR sensors, provide design methods to reach the maximum sensitivity and the way to increase the sensitivity limit. The theoretical analysis shows that metal gratings with periods as large as possible should be used and the incident angle should be set close to 90∘ in order to maximize the sensitivity for a certain detecting wavelength, moreover the sensitivity limit increases as the detecting wavelength increases. Experimentally, we prepare three gratings with periods of 314 nm, 1470 nm and 6733 nm by stripping commercial optical discs or photolithography. The measured sensitivities of the sensors based on these gratings are 319.96 nm/RIU, 1477.74 nm/RIU and 2077.26 nm/RIU, respectively. The sensitivity achieved in this article is much higher than existing ones due to the use of design method following the theoretical analysis. This work paves the way for the optimal design of GCSPR sensors.

Nanocrystalline TiO2 Sensitive Layer for Plasmonic Hydrogen Sensing.

Solution processed TiO2 anatase film was used as sensitive layer for H2 detection for two plasmonic sensor configurations: A grating-coupled surface plasmon resonance sensor and a localized surface plasmon resonance sensor with gold nanoparticles. The main purpose of this paper is to elucidate the different H2 response observed for the two types of sensors which can be explained considering the hydrogen dissociation taking place on TiO2 at high temperature and the photocatalytic activity of the gold nanoparticles.

Wide range bilayer aluminum nanowire grating sensors with robust reflective peaks

A grating-coupled surface plasmon resonance sensor based on bilayer aluminum nanowire arrays is fabricated by laser interference lithography. The device presents impressive reflective sharp peaks by lateral surface plasmon resonances even for aluminum thicknesses of merely several nanometers. Distinct reflective peaks and dramatic color shifts under different analytes are observed within a wide range of incident angle, metal thickness, and refractive index. The sensitivity of 307 nm per refractive index unit is experimentally obtained. The reflective-peak-type surface plasmon resonance sensors are suitable for practical applications because of easy fabrication, low cost, wide range, and high signal visibility.

Thin-film tunable bandpass filter for spectral shift detection in surface plasmon resonance sensors

This Letter proposes the use of a thin-film tunable bandpass filter (TTBF) as an accurate absorption spectral shift detector in surface plasmon resonance (SPR) sensors. The passband central wavelength of the TTBF can be tuned by changing the incident angle. A single TTBF is required to filter two passbands with central wavelengths on the falling and rising curves of the SPR absorption spectrum. The spectral shift can then be converted to the differential intensity change of these two TTBF output beams using the differential detectors to eliminate the common-mode noise. This method can perform a high-resolution sensing for the refractive index change in the SPR sensor surface without using high-performance spectrometers. A grating-coupled SPR sensor was used in the experiment system and achieved a detection resolution of 6.99 × 10 − 6 refractive index unit.

Label-free, real-time on-chip sensing of living cells via grating-coupled surface plasmon resonance

The application of nanotechnologies to address biomedical questions is a key strategy for innovation in biomedical research. Among others, a key point consists in the availability of nanotechnologies for monitoring cellular processes in a real-time and label-free approach. Here, we focused on a grating-coupled Surface Plasmon Resonance (GC-SPR) sensor exploiting phase interrogation. This sensor can be integrated in a microfluidic chamber that ensures cell viability and avoids cell stress. We report the calibration of the sensor response as a function of cell number and its application to monitor cell adhesion kinetics as well as cell response to an external stimulus. Our results show that GC-SPR sensors can offer a valuable alternative to prism-coupled or imaging SPR devices, amenable for microfluidic implementation.

Enhancement and control of surface plasmon resonance sensitivity using grating in conical mounting configuration.

In this work we propose a method to enhance and control the angular sensitivity of a grating coupled surface plasmon resonance (GCSPR) sensor. We lighted a silver grating, mounted in conical configuration, with a laser source and we measured the transmittance of the grating as a function of the azimuthal angle. To evaluate the sensitivity, grating surface was functionalized with four different alkanethiol self assembled monolayers (SAM) and the correspondent azimuthal transmittance peak shifts were measured. The sensitivity control was performed by simply change the light incident angle. This method offers the possibility to design dynamic GCSPR sensor benches that can be used to amplify the SPR angle shift at any step of a biological detection process.

Phase-detection-sensitivity enhancement of grating-coupled surface plasmon resonance sensor with light incident at nonzero azimuth angle

We have numerically and experimentally demonstrated the enhancement of phase detection sensitivity of a grating-coupled surface plasmon resonance (GCSPR) sensor by using incident light at a nonzero azimuth angle. Phase detection measurements were performed using an electro-optic heterodyne interferometer. When the GCSPR sensor was rotated azimuthally by 0 deg and 58 deg, the phase detection sensitivities were approximately 3.2×10−7 RIU and 5.5×10−8 RIU, respectively. The azimuth angle of 58 deg was found to enhance the sensor sensitivity by a factor of 5.87 relative to the azimuth angle of 0 deg.

Phase detection properties of grating-coupled surface plasmon resonance sensors

In this paper, the phase detection properties of a grating-coupled surface plasmon resonance (GCSPR) sensor with a thin metal film on the grating structure has been studied by performing finite-difference time-domain simulation first. Both the metal film thickness and modulation height of the grating considerably affect the phase detection properties of GCSPR sensors. The manner in which the metal film thickness affects the phase curve in the grating-coupled configuration is slightly different from that in the conventional prism-coupled surface plasmon resonance (PCSPR) configuration. For experiment, an electro-optic heterodyne interferometer is used to perform phase detection of the GCSPR sensor and a refractive index resolution of 1.5 × 0(-6) RIU are obtained. The results reveal that the phase detection sensitivity of the GCSPR sensor may be comparable to that of the PCSPR sensor.

High-performance Grating Coupled Surface Plasmon Resonance Sensor Based on Al-Au Bimetallic Layer

A high-performance grating coupled surface plasmon resonance (GCSPR) sensor based on Al-Au bimetallic layer is proposed. High sensitivity is obtained by replacing the positive diffraction order with negative diffraction order of metallic grating to excite the surface plasmon. Compared with the conventional Au-based GCSPR sensor, the sensor with aluminum as the SPR active metal exhibits a sharper (i.e. larger depth-to-width ratio) reflectivity dip, which increases the signal-to-noise ratio (SNR) and enhances its resolution. In addition, an ultrathin gold film is deposited on the grating surface in order to protect the Al layer from getting oxidized. Numerical simulations show that the angular sensitivity of the sensor reaches 187.2°/RIU (degree per refractive index unit) with good linearity and the FWHM (full width at half maximum) of the resonant dip is only 0.93°.

Surface Plasmon Resonance Based on ZnO Nano-grating Structure

We have investigated the grating coupled surface plasmon resonance (GC-SPR) sensors using ZnO nano-grating structures to enhance the sensitivity of an SPR sensor. The GC-SPR sensors were analyzed using the finite-difference time-domain method. The optimum resonance angles of 49 degrees are obtained in the 150 nm wide grating structure with a period of 300 nm for the ZnO thickness of 30 nm. Then, the ZnO nano-grating patterns were fabricated by using laser interference lithography. The measured resonance angle of nano-grating patterns was around 49 degrees. Here, an enhanced evanescent field is obtained due to the surface plasmon on the edge of the bandgap when the ZnO grating structures are used to excite the surface palsmon.