Grating-coupled Surface Plasmon Resonance Research Articles

High spatial resolution surface plasmon resonance imaging using a plasmonic chip.

The surface plasmon resonance (SPR) technique has been widely applied to biosensing technologies for the rapid quantification of biomolecules without enzyme and fluorescent labeling. However, the conventional prism-coupling SPR method generally has a detection area of a few mm2, and the large contribution of the background signal forms a barrier to highly sensitive detection. Based on a highly spatially resolved SPR method, the present study constructed a scanning GC-SPR imaging instrument using an objective lens with a high numerical aperture and a plasmonic chip that could be used for grating-coupled SPR. Focusing light on the diffraction limit can suppress background signals and improve detection sensitivity. SPR imaging can also be performed by scanning a focal spot. Using this method, the refractive index of a mixture of water and dimethyl sulfoxide was measured with a detection accuracy of 2.43 × 10-3 RIU. Polydopamine films prepared with a thickness of <5nm were also measured, and each film thickness was evaluated with high sensitivity from the effective refractive index detected in a small area of <1 µm2.

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.

Rapid and sensitive detection of Candida mannan related to the immune system with a plasmonic sensor chip

To establish a rapid evaluation method for Candida mannan in the saliva, which is a marker molecule of immunity, we develop a fluorescent immunosensor enhanced with grating-coupled surface plasmon resonance using a plasmonic chip i.e., a metal-coated substrate with a wavelength-sized periodic structure. A two-dimensional hole-array chip with two kinds of pitches of 495 nm × 475 nm is used for fluorescence enhancement. The capture antibody is immobilized to the aminated chip surface via a crosslinker with succinimide at both ends, and a stable capture interface is constructed by covalent bonding. Finally, Candida mannan in the standard solution is measured up to 0.1 ng ml−1. Furthermore, in saliva samples, Candida mannan is quantitatively detected between 0.05 and 0.25 ng ml−1, and the highly sensitive detection with the Candida mannan assay system is indicated.

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.

Plasmon resonance measurements in pool boiling, condensation and evaporation experiments on a nanostructured surface

Surface plasmon resonance (SPR) is used in a wide range of applications, including biology, physics and materials science, because of its ability to obtain sub-wavelength measurements from a simple white light source, in real time and non-invasively. Surprisingly, this technique is just beginning to be used in the field of phase change heat transfer, whereas fundamental phenomena occurring near interfaces, such as ice, liquid or vapour nucleation, require the development of innovative techniques capable of reaching this little-explored scale. In this paper, the grating-coupled SPR method is implemented on aluminium samples on which different liquid-vapour phase change phenomena take place. The first goal of this work was the study of the influence of the surface topography on the boiling phenomenon, in particular in the presence of geometrical patterns of micrometric and sub-micrometric scales, typical of those necessary for the implementation of the grating-coupled SPR method. The results show that mirror-polished surfaces covered with periodically structured sub-micrometric grooves have the best thermal characteristics amongst the different surfaces tested, similar to those of a mirror-polished surface with a small number of holes evenly distributed over the surface. Sub-micrometre scale corrugated surfaces being also ideally suited for SPR, they were also used in the second part of the paper to evaluate the potential of this method for the study of boiling, condensation and evaporation. Although our optical SPR test bench, limited by its acquisition frequency, was not able to detect the very fast birth of the first vapour nuclei at the beginning of nucleate boiling, the results yet show the interest of the method as a non-intrusive technique to measure the temperature of the liquid in the very vicinity of the wall, which is also an essential measurement. In addition, measurements from the condensation and evaporation experiments show that SPR provides a useful means to monitor the formation of a nanoscale condensation film and the evaporation of an acetone film in real time. This exploratory study opens perspectives to understand the small-scale phenomena that occur during phase changes and thus help develop functional surfaces that promote or delay their occurrence.

The effect of gold quantum dots/grating-coupled surface plasmons in inverted organic solar cells.

We studied the effect of gold quantum dots (AuQDs)/grating-coupled surface plasmon resonance (GC-SPR) in inverted organic solar cells (OSCs). AuQDs are located within a GC-SPR evanescent field in inverted OSCs, indicating an interaction between GC-SPR and AuQDs' quantum effects, subsequently giving rise to improvement in the performance of inverted OSCs. The fabricated solar cell device comprises an ITO/TiO2/P3HT : PCBM/PEDOT : PSS : AuQD/silver grating structure. The AuQDs were loaded into a hole transport layer (PEDOT : PSS) of the inverted OSCs to increase absorption in the near-ultraviolet (UV) light region and to emit visible light into the neighbouring photoactive layer, thereby achieving light-harvesting improvement of the device. The grating structures were fabricated on P3HT:PCBM layers using a nanoimprinting technique to induce GC-SPR within the inverted OSCs. The AuQDs incorporated within the strongly enhanced GC-SPR evanescent electric field on metallic nanostructures in the inverted OSCs improved the short-circuit current and the efficiency of photovoltaic devices. In comparison with the reference OSC and OSCs with only green AuQDs or only metallic grating, the developed device indicates enhancement of up to 16% power conversion efficiency. This indicates that our light management approach allows for greater light utilization of the OSCs because of the synergistic effect of G-AuQDs and GC-SPR.

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.

Enhancement of organic solar cell performance by incorporating gold quantum dots (AuQDs) on a plasmonic grating.

The incorporation of metallic nanoobjects into devices allows to increase light harvesting, which increases the device performance. In this study, we used a combination of gold quantum dots and grating-coupled surface plasmon resonance (GCSPR) to improve the performance of organic solar cells (OSCs) with a poly(3-hexylthiophene-2,5-diyl) (P3HT):[6,6]-phenyl C61 butyric acid methyl ester (PCBM) photoactive layer. Gold quantum dots with a green fluorescent color (green-AuQD) were loaded into a hole transport layer (HTL) aiming to harvest photons in the UV region and emit visible light into the neighboring photoactive layer. Meanwhile, plasmonic grating structures, which were created on the photoactive layer surfaces via the nanoimprinting technique, provided an enhancement effect through light scattering and GCSPR. Thus, an excellent enhancement of OSC efficiency with a significant increase in short circuit photocurrent (JSC) and power conversion efficiency (PCE) in comparison to that of the reference cell was achieved. The fabricated device provides a JSC value as high as 8.41 mA cm−2 (a 14.11% enhancement) and a PCE value of 3.91% (a 19.57% enhancement). The systematic study clearly reveals that the remarkable enhancement of OSC efficiency is achieved by incorporating both AuQD and plasmonic grating.

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.

Design and Performance of a Composite Grating-Coupled Surface Plasmon Resonance Trace Liquid Concentration Sensor.

In this paper, a grating-coupled surface plasmon resonance concentration sensor employing a gold and indium tin oxide (Au/ITO) nanoparticle composite instead of metal is proposed. The structure and material parameters of the sensor are discussed and analyzed. Taking the ethylene glycol concentration as an example, the influence of the nanocomposite on the wave vector matching, the influence of the refractive index of the medium to be tested and the influence of the concentration on the refractive index were analyzed in detail. The experimental results show that when the sensor is used for the measurement of ethylene glycol concentration, the correlation coefficient between the concentration and the refractive index is as high as 0.999995. The fitting curve and data correlation are good, and the sensitivity has a good linear relationship with the sensitivity. Therefore, the sensor structure proposed in this paper can be used to accurately measure the trace concentration of liquid, and its sensing mode has certain reference value for the measurement of general trace fluid concentration.

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.

Surface plasmon resonance and coloration in stainless steel with a 2D periodic texture

Although stainless steel (STS) is an alloy commonly used in both daily life and the industrial field, little is known about its plasmonic behavior. In this study, we investigated the surface plasmon resonance (SPR) phenomenon in two-dimensionally (2D) textured STS. A 2D periodic grating with a 500 nm pitch was fabricated by imprinting combined with electrochemical etching on the surface of 316L STS plates. Since the fabricated surface texture gave rise to SPR absorption peaks and structural colors, its resonance behavior was characterized in terms of light incident direction and polarization state; the dependence of the SPR wavelengths on these two parameters was theoretically calculated based on the grating-assisted light-coupling mechanism. The experimental results were in good agreement with the theoretical calculations. Grating-coupled SPR can be an effective tool to generate structural colors in STS and may be used in many applications including surface decoration, product identification, and anti-counterfeiting.

Massive Enhancement of Optical Transmission across a Thin Metal Film via Wave Vector Matching in Grating-Coupled Surface Plasmon Resonance.

We demonstrate how distinct surface plasmon resonance modes on opposite sides of a metal-coated grating can be coupled across the metal film. This coupling occurs by matching the resonance conditions on each side of the grating by tuning the refractive index directly adjacent to the metal film. In the first example, we deposited a high refractive index layer of tin oxide on top of the grating to red-shift the front side surface plasmon until it coupled with the backside surface plasmon across a semitransparent ∼45 nm thin silver grating. By shifting the resonance condition of the nearby surface plasmon, this high refractive index coating creates an effective matching of wave vectors across the metal film, allowing them to couple and enhance the optical response. A massive increase in the magnitude of enhanced transmission is observed, increasing from a 6-fold transmission enhancement through a bare silver grating to a near 100-fold enhancement after deposition of a tin oxide layer of appropriate thickness (∼310 nm). This optical transmission enhancement is then probed through computational modeling and by experiments with liquids of various refractive index values. The matched system shows an increased amplitude sensitivity with respect to refractive index changes and a waveguide like behavior within the tin oxide film. As an alternative configuration, we also demonstrate coupling the front and back-side plasmon modes by using a lower refractive index substrate in order to blue-shift the back-side surface plasmon. Coupling between the two plasmon modes is then demonstrated by introducing aqueous solutions of various refractive index values. Under the proper conditions, this matched system also shows a substantial enhancement in transmission. This technique of wave vector matching provides a route to substantially increasing the plasmon enhanced optical transmission through metal gratings, which has potential application in improved plasmonic sensing, spectroscopy, and plasmon-based optical devices.

Enhanced organic solar cell performance: Multiple surface plasmon resonance and incorporation of silver nanodisks into a grating-structure electrode

In this study, plasmonic nanostructures were examined to enhance the light harvesting of organic thin-film solar cells (OSCs) by multiple surface plasmon resonance (SPR) phenomena originating from the grating-coupled configuration with a Blu-ray Disc recordable (BD-R)-imprinted aluminum (Al) grating structure and the incorporation of a series of silver nanodisks (Ag NDs). The devices with such a configuration maximize the light utilization inside OSCs via light absorption, light scattering, and trapping via multiple surface plasmon resonances. Different types and sizes of metallic nanoparticles (NPs), i.e., gold nanoparticles (Au NPs), Ag nanospheres (Ag NSs), and Ag NDs, were used, which were blended separately in a PEDOT:PSS hole transport layer (HTL). The device structure comprised of grating-imprinted-Al/P3HT:PCBM/Ag ND:PEDOT:PSS/ITO. Results obtained from the J–V curves revealed that the power conversion efficiency (PCE) of grating-structured Al/P3HT:PCBM/PEDOT:PSS/ITO is 3.16%; this value is ~6% higher than that of a flat substrate. On the other hand, devices with flat Al and incorporated Au NPs, Ag NSs, or Ag NDs in the HTL exhibited PCEs ranging from 3.15% to 3.37%. Furthermore, OSCs with an Al grating substrate were developed by the incorporation of the Ag ND series into the PEDOT:PSS layer. Compared with that of a reference device, the PCEs of the devices increased to 3.32%–3.59% (11%–20% improvement), indicating that the light absorption enhancement at the active layer corresponds to the grating-coupled surface plasmon resonance and localized surface plasmon resonance excitations with strong near-field distributions penetrating into the active layer leading to higher efficiencies and subsequent better current generation.

Photoluminescence characterization of ZnS-AgInS2 (ZAIS) nanoparticles adsorbed on plasmonic chip studied with fluorescence microscopy

Quantum dots (QDs) are semiconductor nanoparticles showing many advantages for photoluminescence (PL) applications. Since common QDs contain toxic elements such as Cd, Pb, Se, and Te, ZnS-AgInS2 (ZAIS) has been developed as a quantum nanomaterial with low cytotoxicity. In this study, ZAIS@ZnS core-shell QDs coated with carboxyl groups (ZAIS@ZnS-MPA) were prepared as water-soluble nanoparticles. The PL characteristics of ZAIS@ZnS-MPA were studied on a plasmonic chip, which is a substrate with wavelength-scale periodic structures coated with thin metal films, and the PL enhancement of ZAIS by an electromagnetic field derived from grating-coupled surface plasmon resonance (GC-SPR) was also evaluated. The PL spectroscopic characteristics obtained on the grating patterns with a 480 nm-pitch were enhanced in a wider wavelength range. Furthermore, photobleaching, which occurs in conventional fluorescence molecules, was not observed under halogen lamp illumination. The PL and spectroscopic imaging under a microscope indicated the PL characteristics of the ZAIS@ZnS-MPA nanoparticles on the plasmonic chip under appropriate conditions.

Grating-Coupled Surface Plasmon Resonance (GC-SPR) Optimization for Phase-Interrogation Biosensing in a Microfluidic Chamber.

Surface Plasmon Resonance (SPR)-based sensors have the advantage of being label-free, enzyme-free and real-time. However, their spreading in multidisciplinary research is still mostly limited to prism-coupled devices. Plasmonic gratings, combined with a simple and cost-effective instrumentation, have been poorly developed compared to prism-coupled system mainly due to their lower sensitivity. Here we describe the optimization and signal enhancement of a sensing platform based on phase-interrogation method, which entails the exploitation of a nanostructured sensor. This technique is particularly suitable for integration of the plasmonic sensor in a lab-on-a-chip platform and can be used in a microfluidic chamber to ease the sensing procedures and limit the injected volume. The careful optimization of most suitable experimental parameters by numerical simulations leads to a 30–50% enhancement of SPR response, opening new possibilities for applications in the biomedical research field while maintaining the ease and versatility of the configuration.

Experimental demonstration of high sensitivity for silver rectangular grating-coupled surface plasmon resonance (SPR) sensing

We experimentally demonstrated a high sensitivity of surface plasmon resonance (SPR) sensor with silver rectangular grating coupling. The reflection spectra of the silver gratings indicated that surface plasmon resonance can be excited by either positive or negative order diffraction of the grating, depending on the period of the gratings. Comparing to prism-coupled SPR sensor, the sensitivities are higher for negative order diffraction coupling in bigger coupling angle, but much smaller for positive order diffraction coupling of the gratings. High sensitivity of 254.13 degree/RIU is experimentally realized by grating-based SPR sensor in the negative diffraction excitation mode. Our work paves the way for compact and sensitive SPR sensor in the applications of biochemical and gas sensing.

Biosensor platform for parallel surface plasmon-enhanced epifluorescence and surface plasmon resonance detection

For the first time, plasmonic diffraction grating is implemented for the combined direct and epifluorescence-based readout of assays in real-time. This plasmonic structure serves for grating-coupled surface plasmon resonance (SPR) monitoring of molecular binding-induced changes in the refractive index. In parallel, it allows to simultaneously perform plasmonically enhanced fluorescence (PEF) analysis of affinity binding of molecules that are labeled with fluorophores. This configuration offers facile readout of e.g. magnetic nanoparticle-enhanced assays which is not possible with more conventional Kretschmann geometry. The performance characteristics of this combined approach are discussed by using two types of assays. In the first assay a fluorophore-labeled protein with a medium molecular weight of 55kDa was affinity captured on the plasmonic sensor grating. The associated PEF signal in this assay showed a signal-to-noise ratio that was 140-fold higher compared to that of the SPR detection channel. In the second assay, extracellular vesicles were detected by using antibodies against CD81 attached to the plasmonic grating. These vesicles were pre-concentrated by their coupling to magnetic nanoparticles with cholera toxin B chain. This assay exploited magnetic nanoparticles as labels enabling rapid collection of analyte at the sensor surface and for the enhancement of the SPR sensor response. In this case the label-free SPR detection channel outperformed the fluorescence-based detection, as the SPR signal-to-noise ratio was 2.4-fold higher than that of PEF.