Surface Plasmon Resonance Phase Research Articles

Anisotropic Sensing Performance in a High-Sensitivity Surface Plasmon Resonance Sensor Based on Few-Layer Black Phosphorus.

Few-layer black phosphorus (FLBP) is a highly promising material for high sensitivity label-free surface plasmon resonance (SPR) sensors due to its exceptional electrical, optical, and mechanical properties. FLBP exhibits inherent anisotropy with different refractive indices along its two main crystal orientations, the zigzag and armchair axes. However, this anisotropic property is often overlooked in FLBP-based sensors. In this study, we conducted a comprehensive investigation of the SPR reflectivity and phase in a BK7-Ag-FLBP structure to understand the influence of the stacking sequence and the number of FLBP layers on the sensing performance. Clear resonant angle shifts caused by different stacking sequences of FLBP could be observed both theoretically and experimentally. In the theoretical study, the highest reflective and phase sensitivities were achieved with a 12-layer black phosphorus (BP) structure. The reflectivity sensitivity reached 287.9°/refractive index units (RIU) with the zz stacking 12-layer BP film exhibiting a sensitivity 76°/RIU higher than the ac stacking structure. Similarly, the phase sensitivity reached 1162°/RIU with the zz stacking 12-layer BP structure showing a sensitivity 276.9°/RIU higher than the ac stacking structure. The electric field distribution of the 12-layer BP structure with four different stacking sequences has also been analyzed. In the experiment study, the well-known Attenuated Total Reflection (ATR) θ-2θ SPR setup is utilized to detect the reflectivity and phase of BK7-Ag-FLBP structures. The FLBP samples with the same thickness but different stacking sequences show significant resonant angle shift (0.275°) and maximum phase difference variation (34.6°). The FLBP sample thickness and crystal orientations have been demonstrated using the angular-resolved polarized Raman spectroscopy (ARPRS). These theoretical and experimental results provide strong evidence that the stacking sequences of FLBP have a significant impact on the sensing performance of SPR sensors. By harnessing the anisotropic properties of materials like FLBP, novel structures of anisotropic-2D material-based SPR sensors could open up exciting possibilities for innovative applications.

Thickness measurement of bimetallic film using surface plasmon resonance holographic microscopy.

Bimetallic film with high stability and sensitivity is often used to excite surface plasmon resonance (SPR). The thicknesses of the bimetallic film play an important role in quantitative retrieval of the sample's parameters, and a precise measurement method is not available until now. In this paper, we propose a method for measuring the thicknesses of bimetallic film using surface plasmon resonance holographic microscopy (SPRHM). Considering that the refractive index of the dielectric upon the bimetallic film sensitively modulates the SPR phase response, the two thickness parameters of bimetallic film can be calculated by two phase-contrast SPR images with two different liquid dielectrics. The capability of this method was verified with several Ag-Au film couples by using a compact SPRHM setup. Our work provides a precise characterization method for the parameters of SPR configuration and may find wide applications in the research fields of SPR sensing and imaging.

Wavelength sequential selection technique for high-throughput multi-channel phase interrogation surface plasmon resonance imaging sensing.

Phase interrogation surface plasmon resonance (P-SPR) biosensors have the highest sensitivity among different types of surface plasmon resonance (SPR) biosensors. However, P-SPR sensors have small dynamic detection range and complex device configuration. To solve these two problems, we designed a multi-channel P-SPR imaging (mcP-SPRi) sensing platform based on a common-path ellipsometry scheme. A wavelength sequential selection (WSS) technique for P-SPRi sensing is developed to select the optimal sensing wavelengths according to different refractive indexes (RIs) of the samples, so the inconsistency of SPR signal response for different biomolecule types caused by the small dynamic detection range is eliminated. And a dynamic detection range of 3.7×10-3 RIU is achieved, which is the largest among the current mcP-SPRi biosensors. Remarkably, the individual SPR phase image acquisition time has been greatly reduced to 1s by using WSS method instead of whole spectrum scanning, which enables the high-throughput mcP-SPRi sensing.

Label-free and dynamic monitoring of cell evolutions using wavelength-multiplexing surface plasmon resonance holographic microscopy.

Dynamic characterizations of intracellular variations and cell-substrate interactions under different external environments are critical to study cell behaviors and exploring biological applications. However, techniques that are capable of dynamically and simultaneously measuring multiple parameters of living cells in a wide-field manner have rarely been reported. Here, we present a wavelength-multiplexing surface plasmon resonance holographic microscopy which allows wide-field, simultaneous, and dynamic measurements of cell parameters, including cell-substrate distance and cytoplasm refractive index (RI). We use two lasers of 632.8 nm and 690 nm as light sources. Two beam splitters are employed in the optical setup to separately adjust the incident angle of two light beams. Then, surface plasmon resonance (SPR) can be excited for each wavelength under SPR angles. We demonstrate the advances of the proposed apparatus by systematically studying the cell responses to osmotic pressure stimuli from the environmental medium at the cell-substrate interface. The SPR phase distributions of the cell are firstly mapped at two wavelengths, then the cell-substrate distance and cytoplasm RI are retrieved using a demodulation method. Based on phase response differences between two wavelengths and monotonic changes of SPR phase with cell parameters, cell-substrate distance, and cytoplasm RI can be determined simultaneously using an inverse algorithm. This work affords a new optical measurement technique to dynamically characterize cell evolutions and investigate cell properties in various cellular activities. It may become a useful tool in the bio-medical and bio-monitoring areas.

Ultimate phase sensitivity in surface plasmon resonance sensors by tuning critical coupling with phase change materials

Surface plasmon resonance phase interrogation is assumed to be more sensitive than intensity or wavelength interrogation. We propose for the first time theoretical and numerical studies of the phase in surface plasmon resonance sensor and establish a quantitative relation between phase sensitivity and wavelength interrogation. We reveal the link between ultra-high phase sensitivity and critical coupling condition. However, reaching this condition requires a technically infeasible angstrom-level precision in the metal layer thickness. We propose a robust solution to overcome this limitation by coupling the SPR with a phase-change material (PCM) thin film. By exploiting the multilevel reconfigurable phase states of PCM, we theoretically demonstrate ultra-high phase sensitivities with a limit of detection as low as 10−10 refractive index unit (RIU). Such a PCM-assisted SPR sensor platform paves the way for unprecedented sensitivity sensors for the detection of trace amounts of low molecular weight species in biomedical sensing and environmental monitoring.

Phase interrogation SPR sensing based on white light polarized interference for wide dynamic detection range.

A phase surface plasmon resonance (SPR) sensing technology based on white light polarized interference in common-path geometry is reported. A halogen lamp is used as the excitation source of the SPR sensor. The fixed optical path difference (OPD) between p- and s-polarized light is introduced by a birefringence crystal to produce sinusoidal spectral interference fringes. The SPR phase is accurately extracted from the interference fringes using a novel iterative parameter-scanning cross-correlation algorithm. The dynamic detection range is expanded by tracking the best SPR wavelength, which is identified using a window Fourier algorithm. The experimental results show that the sensitivity of this SPR system was 1.3 × 10-7 RIU, and the dynamic detection range was 0.029 RIU. This sensor, not only simple to implement and cost efficient, requires no modulators.

Determination of thin metal film’s thickness and optical constants based on SPR phase detection by simulated annealing particle swarm optimization

Abstract Simulated annealing particle swarm optimization (SAPSO) method for inverse model of optical properties of multilayer thin films based on surface plasmon resonance (SPR) experimental results is introduced in this paper. The purpose is to extract unknown parameters from the phase difference between P- and S- polarizations of the reflected light occurred at the metal/dielectric interface. The results of both the metallic and bimetallic layer derived from our method are in better agreement with the experiment data than particle swarm optimization (PSO) method. Therefore, the approach reveals the possibility of retrieving the thickness and optical constants from the measurement results of the phase difference for multilayers, and makes it be a much better option to be employed for further film’s parameter analysis applications.

Phase-Sensitive Surface Plasmon Resonance Sensors: Recent Progress and Future Prospects.

Surface plasmon resonance (SPR) is an optical sensing technique that is capable of performing real-time, label-free and high-sensitivity monitoring of molecular interactions. SPR biosensors can be divided according to their operating principles into angle-, wavelength-, intensity- and phase-interrogated devices. With their complex optical configurations, phase-interrogated SPR sensors generally provide higher sensitivity and throughput, and have thus recently emerged as prominent biosensing devices. To date, several methods have been developed for SPR phase interrogation, including heterodyne detection, polarimetry, shear interferometry, spatial phase modulation interferometry and temporal phase modulation interferometry. This paper summarizes the fundamentals of phase-sensitive SPR sensing, reviews the available methods for phase interrogation of these sensors, and discusses the future prospects for and trends in the development of this technology.

Spectral Phase Shift of Surface Plasmon Resonance in the Kretschmann Configuration: Theory and Experiment

The spectral phase shift of surface plasmon resonance (SPR) in the Kretschmann configuration is modeled for aqueous solutions of NaCl (analytes) and an SPR structure consisting of gold and chromium layers deposited on an SF10 glass slide. Using the material dispersion of the SPR structure and the analyte, the SPR phase shift, its spectral derivative, and the spectral dependence of the ratio of the reflectances of p- and s-polarized waves are determined for aqueous solutions of NaCl when the concentration of NaCl in water and the refractive index range from 0 to 10 weight percent (wt%) and from 1.3334 to 1.3515 RIU, respectively. In addition, theoretical modeling is accompanied by experiment and the position of a sharp maximum in the measured spectral derivative of the SPR phase shift changes in a range from 596 to 626 nm. From the measurements, a sensitivity to concentration of 3.83 nm/wt% and a detection limit of 7.3 × 10−7 RIU at a wavelength of 612.36 nm are obtained, and very good agreement between theory and experiment is confirmed.

Analysing surface plasmon resonance phase sensor based on Mach-Zehnder interferometer technique using glycerin

Surface Plasmon Resonance (SPR) based on Mach-Zehnder interferometer (MZI) is a very accurate tool for the detection and analysis of molecular interactions. The performance of the proposed SPR phase sensor is dependent upon multiple performance parameters that include sensitivity, repeatability, drift and the induction speed of fluid into the flow cell. The SPR Mach-Zehnder interferometer is tested for different glycerin–water concentrations to check its performance based on the different parameters. This paper highlights the enhancement of the performance of SPR phase technique based on MZI that is influenced by different parameters, measured using glycerin solutions. These four performance parameters can affect the performance of SPR based on MZI and have a particular impact on the sensor output. It also provides us information about suitable working conditions for the SPR Mach-Zehnder interferometer sensor. The experiment data shows that the sensor's sensitivity is high for small concentrations of glycerin–water mixtures. Also, any change in drift as well as in induction speed of fluid can affect the performance of SPR Mach-Zehnder interferometer. The sensitivity of SPR phase sensor is high as it can measure glycerin concentration as low as 0.05%.

The effects of magnetic fields exposure on relative permittivity of saline solutions measured by a high resolution SPR system.

A measurement system for the relative permittivity of a physiological solution under 50 Hz magnetic fields (MF) is presented. It is based on a phase-sensitive surface plasmon resonance (SPR) system. Relative permittivity was analyzed for different solute concentrations of sodium chloride under various MF exposure parameters. We found that MF exposure at 0.2–4.0 mT step-wise decreased significantly the SPR phase signal of a 0.9% sodium chloride solution while 0.1 mT of MF exposure did not. The decreases in the SPR phase signal depended on the duration of MF exposure, and the signal reached a plateau after 15 min of exposure. Interestingly, the decreased SPR phase signal showed a gradual increase and approached the background level when the exposure was drawn off. In addition, we found that the response of the sodium chloride solution to MF also depended on its concentration. In brief, the relative permittivity of sodium chloride in solutions appears to be practically affected by 50 Hz MF exposure. Our data indicates that the relative permittivity of the saline solution influenced by MF exposure should be considered when investigating the biological effects of MF exposure on organisms in experimental study.

Spectral interferometry-based surface plasmon resonance sensor

A two-step spectral interferometric technique is used to measure a surface plasmon resonance (SPR) phase difference from the spectral interferograms recorded in the Kretschmann configuration. The technique employs a polarimetry setup with a white-light source and birefringent crystal and allows one to obtain a channeled spectrum. Two such spectra, one including reflection of p- and s-polarized waves from the SPR structure for air when the SPR phenomenon does not occur in the source spectral range, and the other one for an analyte when the SPR phenomenon occurs, are used to retrieve the wavelength-dependent SPR phase difference. The new method is applied for aqueous solutions of ethanol with different parameters, the concentration of ethanol in water in a range from 0 to 60 weight percent and the refractive index in a range from 1.333 to 1.362. The sensing scheme uses a wavelength interrogation method and the position of a sharp maximum in the spectral derivative of the SPR phase change is measured as a function of the analyte parameter in a range from 644 to 690nm. In the same setup, the spectral dependence of the ratio between the reflectances of both polarization states is measured as a function of the analyte parameter. It is revealed that the detection accuracy of the interferometric measurements is more than three times higher than that of the polarimetric measurements.

Biosensing with gain-assisted surface plasmon-polariton amplifier: A computational investigation

It is known that the development of phase-detecting surface plasmon resonance (SPR) biosensors is impeded by the loss of information due to total photon to surface plasmon polariton transformation at resonance. In this work, a Kretschmann biosensor based on gain-assisted surface plasmon polariton (SPP) amplifier was investigated with analytical and numerical methods. It was found that the gain-assisted SPP amplifying biosensor (SPAB) generated a single emission mode accompanied by a sharp phase jump in the optimal gain condition. The emission wavelength and the phase jump shifted according to the refractive index unit (RIU) change of the analyte. Thus, the SPR phase can be retrieved with unprecedented accuracy and refractive index resolution (RIR) of 1.1×10−11RIU is feasible. Its figure of merit (FOM) for biosensing also attains 1.5×107RIU−1. The predicted RIR and FOM are two orders of magnitude over existing SPR sensors.

Development of phase detection schemes based on surface plasmon resonance using interferometry.

Surface plasmon resonance (SPR) is a novel optical sensing technique with a unique ability to monitor molecular binding in real-time for biological and chemical sensor applications. Interferometry is an excellent tool for accurate measurement of SPR changes, the measurement and comparison is made for the sensitivity, dynamic range and resolution of the different analytes using interferometry techniques. SPR interferometry can also employ phase detection in addition to the amplitude of the reflected light wave, and the phase changes more rapidly compared with other approaches, i.e., intensity, angle and wavelength. Therefore, the SPR phase interferometer offers the advantages of spatial phase resolution and high sensitivity. This work discusses the advancements in interferometric SPR methods to measure the phase shifts due to refractive index changes. The main application areas of SPR sensors are demonstrated, i.e., the Fabry-Perot interferometer, Michelson interferometer and Mach-Zehnder interferometer, with different configurations. The three interferometers are discussed in detail, and solutions are suggested to enhance the performance parameters that will aid in future biological and chemical sensors.

SPR phase detection for measuring the thickness of thin metal films

In this paper, a novel method to determine the thickness of thin metal film is put forward which uses Surface Plasmon Resonance (SPR) phase detection method. The relations between the metal film thickness and the phases of the transverse magnetic (TM) and transverse electric (TE) polarization of the reflected light are shown in the simulation results. By recording the interference patterns which contain the information of the phase differences in the experiments, the values of thickness are calculated. Both of the theoretical analysis and experimental results indicate that the approach presented is feasible and reliable. Thus, it is possible to use the method of phase detection to determine the thickness of thin metal films within 100nm in SPR prism couplers directly with nanometer resolution.

SURFACE PLASMON RESONANCE PHASE-SENSITIVE IMAGING (SPR-PI) SENSOR BASED ON A NOVEL PRISM PHASE MODULATOR

A novel prism phase modulator (PPM) for phase difierence modulation between p- and s-polarization lights in a surface plasmon resonance phase-sensitive imaging sensor is proposed in this paper. The PPM consists of a rhombic prism (to obtain a curve of phase difierence between the two polarizations), a rotation stage and a mirror. The PPM shows great modulation stability and helps to achieve a high detection resolution. Surface plasmon resonance phase imaging is realized with a micro∞uidic device and a CCD camera. Experimental result shows that the detection resolution of our SPR-PI sensor based on phase-interrogation method is 7:61 £ 10 i7 RIU with hydrous samples, which is 16 times improved compared with that based on intensity-interrogation. Real-time monitoring of the interaction between Angiogenin and anti-Angiogenin is also illustrated.

Surface Plasmon Resonance Sensor Using Spectral Interference

This paper presents a novel surface plasmon resonance (SPR) sensor based on whitelight spectral interferometry. The experimental arrangement employs a white-light source (bandwidth from 350 nm to 1000 nm), a polarizer and a birefringent quartz crystal for SPR excitation. SF10 Kretschmann SPR sensor prism is inserted into the beam path and one measures both the corresponding SPR phase change and reflectivity at a suitable fixed angle of incidence across the visible spectrum. The prism (sensing surface) is coated with gold film of 44 nm nominal thickness and the incident angle is approximately 58 . In our case of the SPR effect, the useful phase information is encoded in the spectral interferogram. Thereby, p- and s-polarized spectra interfere among themselves and the interferograms are obtained by using an analyzer when only p-polarized waves are affected by the SPR effect. Spectral interference signals are then used in corresponding phase retrieval [1]. In order to calculate the SPR induced differential phase change, a windowed Fourier transform (WFT) [2] was adopted to extract the phases from two spectral interferograms, one corresponding to the reference material and the other corresponding to the analyte. The pilot measurements were tested with water as an analyte and air as a reference material and the measurement results were compared with the results of theoretical models. The first results show good agreement between a calculated resonance wavelength and a resonance wavelength determined from reflectivity measurements. The second results show good agreement for phase change measurements. The proposed technique offers a much simpler experimental arrangement than was recently presented in a paper [3].

Wavelength-multiplexing phase-sensitive surface plasmon imaging sensor

A wavelength-multiplexing phase-sensitive surface plasmon resonance (SPR) imaging sensor offering wide dynamic detection range and microarray capability is reported. Phase detection is accomplished by performing self-interference between the s- and p- polarizations within the signal beam. A liquid crystal tunable filter is used to sequentially select the SPR excitation wavelength from a white light source. This wavelength-multiplexing approach enables fast detection of the sensor's SPR phase response over a wide range of wavelengths, thereby covering literally any regions of interest within the SPR dip and thus maintaining the highest sensitivity point at all times. The phase-sensitive approach is particularly important for imaging SPR sensing applications because of its less stringent requirements for intensity signal-to-noise ratio, which also means the possibility of using uncooled modest resolution analog-to-digital conversion imaging devices. Experimental results demonstrate a resolution of 2.7×10(-7) RIU with a dynamic range of 0.0138 RIU.

Enhanced sensitivity to surface plasmon resonance phase in wavelength-modulated heterodyne interferometry

An alternative wavelength-modulated heterodyne interferometry based on surface plasmon resonance is proposed for in-situ monitoring of variations in the refractive index of a test sample. Phase variations in surface plasmon resonance are detected by the heterodyne detection system, which uses a wavelength-modulated light source and an unequal-path-length optical configuration. The measurement sensitivity and resolution of the refractive index are greatly enhanced by inserting a quarter-wave plate with a suitable azimuthal angle in front of the SPR sensor. The experimental results indicate that the resolution is better than 3×10−7RIU.

Near Infrared Surface Plasmon Resonance Phase Imaging and Nanoparticle-Enhanced Surface Plasmon Resonance Phase Imaging for Ultrasensitive Protein and DNA Biosensing with Oligonucleotide and Aptamer Microarrays

The techniques of surface plasmon resonance-phase imaging (SPR-PI) and nanoparticle-enhanced SPR-PI have been implemented for the multiplexed bioaffinity detection of proteins and nucleic acids. The SPR-PI experiments utilized a near-infrared 860 nm light emitting diode (LED) light source and a wedge depolarizer to create a phase grating on a four-element single-stranded DNA (ssDNA) microarray; bioaffinity adsorption onto the various microarray elements was detected via multiplexed real time phase shift measurements. In a first set of demonstration experiments, an ssDNA aptamer microarray was used to directly detect thrombin at concentrations down to 100 pM with SPR-PI. Two different ssDNA aptamers were used in these experiments with two different Langmuir adsorption coefficients, K(A1) = 4.4 × 10(8) M(-1) and K(A2) = 1.2 × 10(8) M(-1). At concentrations below 1 nM, the equilibrium phase shifts observed upon thrombin adsorption vary linearly with concentration with a slope that is proportional to the appropriate Langmuir adsorption coefficient. The observed detection limit of 100 pM is approximately 20 times more sensitive than that observed previously with SPRI. In a second set of experiments, two short ssDNA oligonucleotides (38mers) were simultaneously detected at concentrations down to 25 fM using a three-sequence hybridization format that employed 120 nm DNA-modified silica nanoparticles to enhance the SPR-PI signal. In this first demonstration of nanoparticle-enhanced SPR-PI, the adsorbed silica nanoparticles provided a greatly enhanced phase shift upon bioaffinity adsorption due to a large increase in the real component of the interfacial refractive index from the adsorbed nanoparticle. As in the case of SPR-PI, the detection limit of 25 fM for nanoparticle-enhanced SPR-PI is approximately 20 times more sensitive than that observed previously with nanoparticle-enhanced SPRI.