Techniques for signal analysis in surface plasmon resonance sensors

A method to enable surface plasmon resonance (SPR) sensors to discriminate between bulk and surface-localized refractive index changes is demonstrated with modified gold-coated tilted fiber Bragg grating SPR sensors (TFBG-SPR). Without this capability, all high-resolution SPR sensors should be using reference channels and strict temperature control to prevent the contamination of the desired detection of surface-localized chemical or binding events by drift of the refractive index of the medium, in which the experiment is carried out. The very fine comb of high-quality-factor resonances of a TFBG-SPR device coupled to the large differential sensitivity of some of the resonances to various perturbations is used to measure unambiguously the refractive index changes within a surface layer thinner than 25 nm from those of the bulk surrounding. The enabling modification of the conventional TFBG-SPR is a reduction of the gold coating from its optimum value near 50-30 nm: at this lower thickness, a surface plasmon wave can still be excited by a limited number of cladding mode resonances, but at the same time, the metal is thin enough to allow modes away from the SPR to tunnel across the metal and probe the bulk RI value. Measurements and simulations of the deposition of a self-assembled monolayer of 1-dodecanethiol in ethanol show that the bulk refractive index changes as small as 0.0004 can be distinguished from the formation of a 1 nm thick coating on the surface of the fiber.

Sensitivity enhancement in erbium-doped fiber laser intra-cavity SPR sensor

This paper presents low-cost, multi-channel, nano-grating SPR (Surface Plasmon Resonance) sensor chips for applications to disposable biomolecule detection. The present SPR sensor chip consists of two fluidic channels, including a sample channel and a reference channel, each having 833 nm-pitch PDMS gratings. The SPR signals from each channel are coupled by an external mirror and the SPR dip shift in the coupled signals is detected by a single spectrometer. Compared to the previous multi-channel SPR sensors using fiber-optic switches or special prisms, the present SPR sensor chips with PDMS nanogratings result in more compact and less expensive SPR detectors. We have designed and fabricated the SPR sensor chips with two channel gratings having the refractive index sensitivity of 321.78 nm/RI and 514.26 nm/RI, respectively. From the fabricated SPR sensor chips, we measure the SPR dip shift of 1.13±0.16 nm for the target biomolecules of 0.5 μM streptavidin binded on a 10% biotinylated surface. The real-time binding reaction rates of m-antibiotin has been monitored for the fixed concentration of 0.2 μM streptavidin as well as for the varying concentration range of 2-50 nM; thus obtaining the results for the fixed and varying concentration in good agreement with those obtained from a commercialized SPR sensor. It is demonstrated that the polymer nanograting SPR sensor chips offer simple and disposable biomolecule detection methods for point-of-care applications. [DOI: 10.1380/ejssnt.2009.750]

To address the problems that the surface plasmon resonance (SPR) sensor is not sensitive enough to detect biomolecules in the refractive index range (RI=1.33-1.34), and the traditional methods to enhance the sensitivity cause the sensor poor bioaffinity, this paper proposed raspberry-like silica assisted high figure of merit (FOM) fiber-optic SPR sensor. The finite element method results show that when the raspberry-like silica is introduced to the SPR sensor, the resonant electric field intensity on the sensor surface is 2.97 times stronger than that of SPR sensors only. Raspberry-like silica particles composed of different noble metals nanoparticles (AuNPs, PtNPs, and CuNPs) were prepared to compare and analyze the effects of different nanoparticles on the sensing performance. The sensing experiments showed that AuNPs raspberry-like silica had the most excellent performance, enabling the sensor to achieve high sensitivity of 5264.3 nm/RIU, which is 2.65 times higher than the Au film SPR sensor. The fitting calculations showed that the AuNPs raspberry-like silica assisted SPR sensor had a high FOM of 42.9 RIU-1, 1.9 times more than the Au film SPR sensor. In addition, the sensor has good temperature stability, repeatability, and generality after the corresponding test. The proposed raspberry-like structure provides a new approach to obtaining both high sensitivity and high FOM for the SPR sensor, which makes the sensor potential for biosensing.

The fiber surface plasmon resonance (SPR) sensor is widely used in high-sensitivity refractive index detection, and there are few reports on SPR sensors used for strain measurement. In this paper, we propose and demonstrate an S-type fiber strain sensor based on SPR. The simulation and testing results indicate that the smaller the vertical axis offset of S-type fiber is, the larger the incidence angle of SPR is, and the closer the working band of SPR is to the shorter wavelength direction. By electrofusion, we fabricated an S-type structure on the single-mode fiber, and by the S-type structure, the high-order cladding mode was excited. A 50 nm gold film was coated on the surface of the fiber cladding behind the S-type structure. The evanescent field of the cladding mode contacted the gold film to produce SPR, and the strain can change the vertical axis offset of the S-type fiber and further change the incidence angle of SPR; hence an S-type fiber strain sensor based on SPR was realized. When the refractive index of the ambient medium is 1.345 RIU, the vertical axis offset and length of the S-shaped structure are 87 and 501 µm, respectively, the resonance wavelength of the fiber SPR strain sensor changes from 648.06 to 631.77 nm with a strain detection range of 0-1200µε, and its sensitivity is -14.38pm/µε. The proposed sensor provides a new solution for the strain measurement of the fiber SPR sensor, which is expected to be used in the fields of engineering, health monitoring, and early warning.

A surface plasmon resonance sensor with synthetic receptors decorated on graphene oxide for selective detection of benzylpenicillin

A transmission-type surface plasmon resonance (SPR) sensor is presented. In the transmission-type SPR structure, surface plasmon waves are outcoupled to radiation modes by the use of dielectric grating on a thin-film layer of Ag. Compared with the traditional reflection-type SPR sensor, the new method provides larger detectable range, which might be useful to investigate thick targets such as in cell analysis. Theoretical simulations show that the structures provide high transmission efficiency for surface plasmon resonance and the devices present extremely linear sensing characteristics. Furthermore, it is found that the transmission efficiency and the refractive index detection sensitivity of the SPR sensor can be improved by the use of a lower refractive index glass prism.

Computational study: Windmill-shaped multi-channel SPR sensor for simultaneous detection of multi-analyte

MoS2-nanoflower enhanced programmable adsorption/desorption plasmonic detection for bipolar-molecules with high sensitivity

In this paper, a theoretical analysis of figure of merit (FOM) of a surface plasmon resonance (SPR) sensor with a buffer layer of magnesium fluoride has been carried out. While the FOM is the ratio of sensitivity and full width at half maximum and it is the measurement index for the SPR performance. The numerical simulation is based on side polished single mode fiber SPR sensor with the 66.5 μm residual fiber thickness and Drude model of metal with the 50 nm gold film thickness. Meanwhile, the comparisons for traditional surface plasmon resonance sensor, symmetrical surface plasmon resonance sensor and long range surface plasmon resonance sensor have performed differently for the FOM. The effect of sensitivity, full width at half maximum and transmittance depth has also been studied. All these studies, lead to a significant analysis to achieve the best possible design of a fiber optic SPR sensor with maximum FOM while the thickness of buffer layer is 100 nm. This design is expected to play an important role on chemical sensing and biological sensing.

An optical-absorption-based surface plasmon resonance (SPR) sensor is proposed, and its theoretical aspects are discussed in terms of mathematical descriptions and numerical simulations of the SPR curve. The response theory of the absorption-based SPR sensing is based on the expansion of Kretchmann's SPR theory into the case in which optical absorption in the sensing layer is expressed by the Lorentz model. The numerical simulations were performed using a three-layer Fresnel equation of p-polarization. It was found that SPR curve behavior of the absorption-based SPR sensor depends on the frequency relation between the light source and the optical absorption and the thickness of the metal layer. The SPR curve behavior is divided into three types according to the large, small, and equal relations between excitation and absorption frequencies. Each type of behavior is further divided into two types that are due to thin and thick metal layers. The theory of this new type of sensor based on optical absorption was explained and demonstrated by the simulation of the SPR curves using optical parameters relating to a silver-metal-based SPR sensor.

Surface plasmon resonance (SPR) sensor has been widely investigated as an exceedingly powerful tool for biological and chemical detection in the past decay. As an essential component of both academic and commercial laboratories, several methods have been employed to monitor the excitation of SPR by measuring the light reflected from the sensor interface including modulation of angle, wavelength, intensity, phase and polarization. Among these methods, angle modulation (AM) and wavelength modulation (WM) are the most widely adopted in practice. However, the normal sensors system of the angle modulation was built by two ratable stages with a flow cell attaching a prism, and the angle of incidence rottingθ, the angle of reflect rotting 2θ. The mechanical structure can only be used in the angle modulation SPR sensor. In the present study, a new SPR is designed by a mechanical structure which can transform freely from wavelength to angle modulation. The different concentration Ethanol solution is tested by this system, and the linear range is very well from the volume ratio 0% to 60%. The primary application is done in real time detection of human IgG and antibody interaction, and the experimental results indicate that the new SPR system can detect human antibody at low concentration 1x10^-11g/ml with highly sensitivity and flexibility. The new SPR system is of great importance for potentially practical application in biosensor and life science with the extended the functions of the conventional SPR sensor, and provides the real-time and in-situ detection of the biomolecules.

Magnetized SPR sensor for enhanced functionality

Surface plasmon resonance (SPR) sensors have fascinated impressive attention to detect clinically related analytes in recent years. SPR sensors have also multiple advantages over existing conventional diagnostic tools such as easy preparation, no requirement of labeling, and high specificity and sensitivity with low cost, and they provide real-time detection capability. There are some articles and reviews in literature focusing on the applications of SPR-based sensors for the diagnosis of medically important entities such as proteins, cells, viruses, disease biomarkers, etc. These articles generally give information on the determination of such structures merely, whereas this presented manuscript combines recent literature for most of the medically important structures together including proteins, hormones, nucleic acids, whole cells, and drugs that especially the latest applications of SPR sensors for medical diagnosis to follow up new strategies and discuss how SPR strategy is brought to solve the medical problems.

A surface plasmon resonance (SPR) sensor with a prism array made by silicon microfabrication techniques is proposed. We fabricated silicon prisms arrayed in 200 µ m in pitch by anisotropic wet etching for deflecting light. We measured SPR curves in specimen of air, water and ethanol using near-infrared laser light (1550 nm) and obtained the SPR dip in each measurement. We fabricated a flexible flap, which was actuated by Lorentz force, to change the incident angle. The silicon prism chip was attached on the flap, the SPR curve was measured by scanning the incident angle of laser light with the flap.