Compact Surface Plasmon Resonance Research Articles

Common-mode plasmon sensing scheme as a high-sensitivity compact SPR sensor.

A deep metal grating enables quasi-phase-matched simultaneous excitation of two counterpropagating surface plasmon modes by means of its +1st and -2nd diffraction orders. The resulting angular reflection spectra of the scattered -1st and zeroth orders exhibit three interleaved zeros and maxima in a range centered around the Littrow angle. The spectra differ thoroughly from the usual reflection dip resulting from single-order plasmon coupling that produces strong absorption. The zeroth and -1st orders exhibit two crossing angles enabling high-sensitivity common-mode detection schemes designed to reject variations in source power and environmental noise. The proof of concept and experimental assessment of this new surface plasmon resonance (SPR) sensing scheme are demonstrated by monitoring gases in a pressure-controlled chamber. A limit of detection (LOD) of 2 × 10-7 refractive index unit (RIU) was achieved.

SPECTRA: A Novel Compact System for Surface Plasmon Resonance Measurements.

Surface plasmon resonance (SPR) is a common and useful measurement technique to perform fast and sensitive optical detection. SPR instrumentations usually comprise optical systems of mirrors and lenses which are quite expensive and impractical for point-of-care applications. In this work, we presented a novel and compact SPR device called SPECTRA, designed as a spectrophotometer add-on with a grating coupling configuration. The device is conceived as a marketable solution to perform quick SPR measurements in grating configuration without the requirement of complex instrumentation. The device can be customized either in a vertical structure to reach lower incident light angles, or in a horizontal configuration, which is suitable for SPR analysis using liquid solutions. The SPECTRA performance was evaluated through SPR measurements in typical applications. The vertical SPECTRA system was employed to detect different functionalization molecules on gold 720 nm-period grating devices. Meanwhile, the horizontal SPECTRA configuration was exploited to carry out fluid-dynamic measurements using a microfluidic cell with glycerol solutions at increasing concentrations to account for different refractive indexes. The experimental tests confirmed that the SPECTRA design is suitable for SPR measurements, demonstrating its capability to detect the presence of analytes and changes in surface properties both in static and dynamic set-ups.

No-core fiber surface plasmon resonance dual-channel sensor for refractive index and temperature sensing with compact structure

To improve the integration of sensors and meet the trend of miniaturization of devices, we propose and demonstrate a compact dual-channel surface plasmon resonance (SPR) fiber sensor for detecting refractive index (RI) and temperature. In this sensor, we chose the simplest structure of optical fiber: no-core fiber (NCF), as the sensing probe. Then the silver film was deposited on the NCF surface using magnetron sputtering to excite the SPR effect. Two sensing channels were constructed on the NCF, one channel deposited with silver film for RI detection, and another channel deposited with PDMS and silver film for temperature detection. Such a construction makes the sensor compact and small. The performance of the proposed sensor is studied theoretically and experimentally. The experiment shows that the maximum sensitivity of the sensor is 3039 nm/RIU and 3.53 nm/°C when the RI ranges from 1.333 to 1.375 and the temperature ranges from 0 °C to 70 °C, respectively. The significant advantage of our proposed sensor is its simple, compact, and easy-to-prepare structure, which opens up a new direction for device miniaturization.

Compact surface plasmon resonance sensor using the digital versatile disc grating as a coupler and a disperser

Compact surface plasmon resonance (SPR) sensors are highly demanded due to their small size, low cost, and wide application scenarios compared with benchtop sensors. To realize high-precision spectral or angular analysis, most compact SPR sensors need spectrometers or rotation stages, which increase the cost of the device. We demonstrate a low-cost and compact SPR sensor by utilizing a single grating as a coupler and a disperser. The polychromatic light emitted from a light-emitting diode was coupled to surface plasmon modes by a grating made from a digital versatile disc-recordable disc. The light was dispersed by the same grating and collected by a linear charge-coupled device. The real-time detection of the SPR spectra and the resonant wavelengths was realized by homemade software based on the laboratory virtual instrument engineering workbench. By measuring different concentrations of glucose solution and sodium chloride solution, we obtain a high refractive index (RI) resolution of 5.52 × 10 − 5 RI unit. This compact SPR sensor can be applied in the areas of food safety, environmental monitoring, medical diagnosis, and so on.

Proposal of compact LSPR sensor system by filter-free wavelength sensor

A compact localized surface plasmon resonance (LSPR) sensor system integrated with a filter-free wavelength sensor (FFS) for quantitative virus detection methods was demonstrated. The changed transmission spectrum of the LSPR sensor by molecule was measured using an FFS as a transducer without a conventional spectrometer. We designed and fabricated gold nanostructures optimized for virus detection. As the concentration of S-protein RBD changed from 0.1 to 10 ng ml−1, the change in the current ratio from 0.012 to 0.094 was obtained by the FFS. We expect a compact and rapid virus detection system with qualitatively diagnose to be realized using the proposed method.

Simultaneous measurements of refractive index and temperature based on a no-core fiber coated with Ag and PDMS films

A compact surface plasmon resonance (SPR) fiber optic sensor, being utilized to simultaneously measure refractive index (RI) and temperature, is proposed and experimentally demonstrated in this paper. One part of a no-core fiber (NCF) was coated with a silver (Ag) film, and the other part was coated with a silver/polydimethylsiloxane (Ag/PDMS) composite film to stimulate the SPR effect. Due to the two heterogeneous films, two dips appeared in the transmission spectrum and were used to achieve the dual-parameter measurements. The experimental results showed that the RI sensitivity reached 2121.43 nm/RIU and 0 nm/RIU, while the temperature sensitivity reached –0.32 nm/°C and –2.21 nm/°C for the two dips, respectively. Based on the obtained transfer matrix, the measurements of RI and temperature could be demodulated. This designed sensor showed the merits of simple structure, easy to implement, and high sensitivity, demonstrating application prospects in dual-parameter monitoring.

Compact Surface Plasmon Resonance IgG Sensor Based on H-Shaped Optical Fiber

A compact surface plasmon resonance sensor based on an H-shaped optical fiber is proposed and demonstrated. The H-shaped optical fiber was fabricated experimentally by using hydrofluoric acid to controllably corrode the polarization-maintaining fiber. A satisfactory distance between the outer surface of the fiber and the core can be achieved, and then the surface plasmon resonance effect can be excited by coating a metal film of appropriate thickness on the surface of the fiber. This technology can realize the preparation of multiple samples at one time, compared to the traditional side-polishing technique. The H-shaped optical fiber obtained from corrosion exhibits a high surface quality and short lengths, down to only a few hundred microns. The effects of the proposed H-shaped optical fiber on spectral properties are induced by process parameters, including fiber remaining thickness, coating thickness and fiber length, and were investigated in detail. The prepared sensor was used for the specific detection of human IgG, and the minimum human IgG concentration that the sensor can distinguish is 3.4 μg/mL. Such a compact surface plasmon resonance fiber sensor has the advantages of an easy fabrication, good consistency and low cost, and is expected to be applied in the specific detection of biomarkers.

A Compact Surface Plasmon Resonance Biosensor for Sensitive Detection of Exosomal Proteins for Cancer Diagnosis.

Exosomes are nanosized (50-150nm) extracellular vesicles released by all types of cells in the body. They transport various biological molecules, such as DNAs, RNAs, proteins, and lipids from parent cells to recipient cells for intercellular communication. Exosomes, especially those from tumor cells, are actively involved in caner development, metastasis, and drug resistance. Recently, many studies have shown that exosomal proteins are promising biomarkers for cancer screening, early detection and prognosis. Among many detection techniques, surface plasmon resonance (SPR) is a highly sensitive, label-free, and real-time optical detection method. Commercial prism-based wavelength/angular-modulated SPR sensors afford high sensitivity and resolution, but their large footprint and high cost limit their adaptability for clinical settings. We have developed an intensity-modulated, compact SPR biosensor (25cm×10cm×25cm) for the detection of exosomal proteins. We have demonstrated the potential application of the compact SPR biosensor in lung cancer diagnosis using exosomal epidermal growth factor receptor (EGFR) and programmed death-ligand 1 (PD-L1) as biomarkers. The compact SPR biosensor offers sensitive, simple, fast, user-friendly, and cost-effective detection of exosomal proteins, which may serve as an in vitro diagnostic test for cancer.

Micro-Lab on Tip: High-Performance Dual-Channel Surface Plasmon Resonance Sensor Integrated on Fiber-Optic End Facet

It is a challenging and valuable work to realize the simultaneous sensing of two or more parameters at the end of optical fiber. In this paper, we implemented an ultra compact dual-channel surface plasmon resonance (SPR) sensor on fiber-optic end facet. A dual-layer polymer microcap based on different refractive index (RI) films was used to segment a single Cu/TiO2 coated micro-cone on single mode fiber (SMF) end facet for producing a sensing spectrum with two separated SPR dips. The SPR dip (channel-II) generated by Polydimethylsiloxane (PDMS) microcap can reach high sensitivity temperature measurement of 2.935 nm/°C in the range of 30–70 °C, and the SPR dip (channel-I) generated by polyvinyl alcohol (PVA) microcap can achieve high sensitivity humidity measurement of 1.08 nm/%RH in the range of 20%RH-70%RH. Finally, the simultaneous detection of humidity and temperature can be realized by the matrix established by channel-I and channel-II. This is a simple, effective and reproducible micro laboratory on optical fiber end facet for dual parameter sensing.

V groove fiber plasmonic sensor with facile resonance tunability

A compact and ultra-convenient fiber optic surface plasmon resonance sensor is proposed here, deploying a V groove fiber. The open V groove simultaneously acts as a microfluidic channel and core, when it is filled with analytes having high refractive index (RI) whereas plasmons are generated by placing a gold nanowire inside the groove. The characteristics of the sensor have been analyzed using the finite element method and the results demonstrate maximum possible wavelength sensitivity of 20,400 nm/RIU, amplitude sensitivity 700 RIU−1 with corresponding wavelength resolution in the order of 10−6 RIU. Further, the sensor is capable of detecting a wide analyte RI ranging from 1.455 to 1.5 and provides easy tunability of both plasmonic resonance and mode loss without modifying the fiber geometry. So, the proposed sensor could be a potential alternative to the state of art high RI fiber sensors due to its convenient design, easy fabrication procedure, and competitive sensing performance.

Numerical Analysis of Dual-Parameter Optical Fiber Sensor With Large Measurement Range Based on Surface Plasmon Resonance

Multi parameter measurement and device miniaturization are the development trend of optical fiber sensors. Here we propose a compact dual channel surface plasmon resonance (SPR) fiber sensor which can measure the liquid refractive index (RI) and ambient temperature in real time. This sensor coats metal and polydimethylsiloxane (PDMS) on the side of a no-core D-shaped fiber: the channel for measuring the liquid RI is covered by silver film, and the channel for temperature sensing is covered by gold film and PDMS. The sensing sensitivity is analyzed by finite element method. When the liquid RI is within 1.33~1.44 and the temperature is within 0~180 °C, the corresponding maximum spectral sensitivity is 12530 nm/RIU and −3.465 nm/°C, respectively. The sensor has wide detection range, compact structure and temperature compensation function, which is suitable for environmental monitoring and high-precision sensing.

Optimization of plasmonic sensors based on sinusoidal and rectangular gratings

Surface plasmon resonance (SPR) sensors based on metal gratings have received much attention for designing compact and portable biosensors. In this paper, we systematically optimize SPR sensors based on sinusoidal and rectangular gratings to improve the performance of this kind of sensors. A parameter (FOM*) is defined to evaluate the sensor performance, which combines the sensitivity, FWHM, and depth of the SPR absorption peak. We find that grating period of 560 nm is suitable to locate the SPR peaks in the optimal response range of silicon detectors and ensures high sensitivity. For sinusoidal gratings, the highest FOM* of 99.25 is achieved at grating depth of 15 nm. The highest FOM* for rectangular grating with continuous metal film is 123.70 when grating depth and duty cycle are 12 nm and 0.3, respectively. With grating depth of 24 nm and duty cycle of 0.8, the highest FOM* of 25.23 is obtained for rectangular grating with discontinuous metal film. These optimization results can be directly used to improve the detection limit of compact SPR sensors.

A versatile and compact surface plasmon resonance spectrometer based on single board computer.

The widespread diffusion of low-cost but high-performance hardware is enhancing the realization of scientific equipment with features at the research laboratory level. In this paper, we demonstrate hardware implementation of a surface plasmon resonance compact device with high accuracy and measurement times appropriate for many applications. Image acquisition is realized by a Raspberry Pi single board computer with a camera module, and a Python code is used to process data. A flexible optical setup can work in two different configurations, namely, the inspection mode and angle resolved measurement mode. The inspection mode is used to precisely locate the light-emitting diode interrogation beam on the sample, avoiding uneven or faulty regions. The measurement mode allows us to monitor in real time the position of the minimum reflectivity with subpixel resolution. Performance tests show a resolution in the bulk refractive index of 4.9 × 10-6 refractive index units for 10 s acquisition time.

Novel polymer waveguide-based surface plasmon resonance (SPR) sensor

A novel polymer waveguide for surface plasmon resonance (SPR) sensing is theoretically proposed and experimentally demonstrated. The waveguide sensor simply consists of a polymer and a thin gold film on a silica layer. According to the multilayer transfer-matrix theory and the multiple reflection theory, a formula describing the reflectivity of total light power is deduced and analyzed, which is related to the dielectric constant of both the waveguide and the metal, the thickness of the metal film, and the length of the sensing area. By the addition of liquids with refractive indices ranging from 1.40 to 1.47 in the sensing area, the proposed polymer waveguide-based surface plasmon resonance sensor exhibited an experimental sensitivity of 1489 dB/RIU. With a refractive index range between 1.45 and 1.47 beyond the measurement range of typical SPR fiber based sensors, the reported device operates with very high sensitivity. The proposed portable, compact, and simple polymer waveguide-based surface plasmon resonance sensor shows potential for low cost and on-chip multiple channel sensing for practical applications.

V-shaped micro-structure optical fiber surface plasmon resonance sensor for the simultaneous measurement of the refractive index and temperature.

We propose and demonstrate a novel and compact optical fiber surface plasmon resonance (SPR) sensor for the simultaneous measurement of the refractive index (RI) and temperature. The sensor is fabricated by employing the eccentric-core fiber (ECF), which is polished to a V-shaped micro-structure optical fiber (MOF). One side of the MOF is used as the RI sensing channel, and the other side is used as the temperature sensing channel. Two sensing channels are independent without crosstalk. The sensor has high RI sensitivity up to the maximum of 3376nm/RIU from 1.333 to 1.385RIU, and high-temperature sensitivity up to -2.65 nm/°C from 20°C to 60°C. In addition, owing to the few-mode light in the ECF, the full width at half-maximum is smaller than other SPR sensors based on multimode fiber. This sensor will be extremely helpful to improve the RI measurement uncertainty caused by temperature disturbance.

Abstract 1983: Cancer exosomes immunosuppressive activity in the absence of contaminating soluble factors is multifactorial

Abstract Cancer derived exosomes, along with soluble factors such as growth factors, cytokines and chemokines have been identified as integral immunosuppressive pathways employed by cancer cells. Using melanoma cell lines as a model for generating human melanoma exosomes (HMEX), we studied the soluble factors associated with exosome purification methods. A Luminex 13-plex T cell activation kit was used to detect the presence of soluble factors in exosome isolates. We have demonstrated that combining Ultrafiltration and Size Exclusion Chromatography (REIUS method) can yield up to 58-fold more exosomes than ultracentrifugation (UC) with greatly reduced concentrations of contaminating soluble factors (IL-8: 4.6 pg/ml by REIUS versus 489 pg/ml by UC | IL-10: 1,052 pg/ml by REIUS versus 34,500 pg/ml by UC). A novel exosome-based Compact Surface Plasmon Resonance Biosensor demonstrated that REIUS-isolated exosomes abundantly express PD-L1 on their surface compared to UC-purified exosomes. These HMEX significantly inhibited a cloned NY-ESO tumor antigen-specific patient derived T cell function when co-cultured with a NY-ESO positive melanoma cell line for 4 h (IFN-γ positive T cell population: 78.5 ± 0.03 % versus 49.05 ± 0.07 %). Blocking with anti-PDL1 or anti-IL-10 failed to restore T cell function (IFN-γ production), while both anti-PD-L1 and anti-IL-10 antibodies partially reverse this suppression, thereby identifying IL-10 and PD-L1 as a novel collaborating inhibitory pathway. Taken together, we report that different exosome isolation methods impact the nature of the exosomes and contaminating soluble factors and should be chosen with caution. In addition, our data suggests a novel role for tumor-derived exosomes in the IL-10 and PD1-PDL1 axis crosstalk that impacts functional activity of T cells. Citation Format: Shin La Shu, Junko Matsuzaki, Cheryl Allen, Yunchen Yang, Edward Hurley, Kunle Odunsi, Yun Wu, Marc S. Ernstoff. Cancer exosomes immunosuppressive activity in the absence of contaminating soluble factors is multifactorial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1983.

Surface plasmon resonance sensor based on coreless fiber for high sensitivity

A compact and simple surface plasmon resonance sensor based on coreless fiber for refractive index measurement is developed. Compared with common SPR sensors, the proposed SPR sensor has a shorter length of 1 cm, avoids a taper and can be used to detect a wider range of 1.335–1.4019. The resonant wavelength shifts ∼200 nm to the longer wavelength in the refractive index range of 1.3335–1.4019. The average refractive sensitivity of 2836 nm/RIU is obtained in the range of 1.3335–1.4019, and the highest sensitivity can reach 4328.2 nm/RIU. Furthermore, our device has the advantages of small size, wide measuring range, excellent stability and short response time, which is appropriate for biological sensing.

Ochratoxin A detection in coffee by competitive inhibition assay using chitosan-based surface plasmon resonance compact system.

This study demonstrates the evaluation of ochratoxin A (OTA) in coffee on compact surface plasmon resonance (SPR) biosensors based on crosslinked chitosan and carboxymethyl chitosan nanomatrix substrates. Ochratoxin A is a toxic secondary metabolite widely produced by Aspergillus and Penicillium fungi and requires regular quantification and detection in food samples. The gold coated SPR chips were synthesized with chitosan and carboxymethyl chitosan through spin coating technique. The SPR nanomatrix chips were used for the immobilization of ochratoxin A-bovine serum albumin (OTA-BSA) conjugate to develop a competitive inhibition immunoassay. The monoclonal ochratoxin A antibodies (mAb-OTA) were used as biological receptors for the detection of OTA in buffer and coffee samples. The limit of detection (LOD) in coffee for chitosan (CS) and carboxymethyl chitosan (CMC) substrates was 5.7 ng/mL and 3.8 ng/mL, respectively. Compact surface plasmon resonance (SPR) system based on chitosan-based (CS-AU) nanomatrix substrates provides a platform for the detection of ochratoxin A with high sensitivity, accuracy, ease-of-use and cost-effectiveness. This compact SPR system can be used at farm and industrial levels for the detection of OTA in food matrices.

Sensitive Detection of Exosomal Proteins via a Compact Surface Plasmon Resonance Biosensor for Cancer Diagnosis.

Exosomes are small extracellular vesicles released by cells for cell-cell communication. They play important roles in cancer development, metastasis, and drug resistance. Exosomal proteins have been demonstrated by many studies as promising biomarkers for cancer screening, diagnosis, and monitoring. Among many detection techniques, surface plasmon resonance (SPR) is a highly sensitive, label-free, and real-time optical detection method. Commercial prism-based wavelength/angular-modulated SPR sensors afford high sensitivity and resolution, but their large footprint and high cost limit their adaptability for clinical settings. Recently, a nanoplasmonic exosome (nPLEX) assay was developed to detect exosomal proteins for ovarian cancer diagnosis. However, comparing with conventional SPR biosensors, the broad applications of nanoplasmonic biosensors are limited by the difficult and expensive fabrication of nanostructures. We have developed an intensity-modulated, compact SPR biosensor (25 cm × 10 cm × 25 cm) which uses a conventional SPR sensing mechanism and does not require nanostructure fabrication. Calibration from glycerol showed that the compact SPR biosensor offered sensitivity of 9.258 × 103%/RIU and resolution of 8.311 × 10-6 RIU. We have demonstrated the feasibility of the compact SPR biosensor in lung cancer diagnosis using exosomal epidermal growth factor receptor (EGFR) and programmed death-ligand 1 (PD-L1) as biomarkers. It detected a higher level of exosomal EGFR from A549 nonsmall cell lung cancer (NSCLC) cells than BEAS-2B normal cells. With human serum samples, the compact SPR biosensor detected similar levels of exosomal EGFR in NSCLC patients and normal controls, and higher expression of exosomal PD-L1 in NSCLC patients than normal controls. The compact SPR biosensor showed higher detection sensitivity than ELISA and similar sensing accuracy as ELISA. It is a simple and user-friendly sensing platform, which may serve as an in vitro diagnostic test for cancer.

Real-time biodetection using a smartphone-based dual-color surface plasmon resonance sensor.

We proposed a compact and cost-effective red-green dual-color fiber optic surface plasmon resonance (SPR) sensor based on the smartphone. Inherent color selectivity of phone cameras was utilized for real-time monitoring of red and green color channels simultaneously, which can reduce the chance of false detection and improve the sensitivity. Because there are no external prisms, complex optical lenses, or diffraction grating, simple optical configuration is realized. It has a linear response in a refractive index range of 1.326 to 1.351 (R2 = 0.991) with a resolution of 2.3 × 10 - 4 RIU. We apply it for immunoglobulin G (IgG) concentration measurement. Experimental results demonstrate that a linear SPR response was achieved for IgG concentrations varying from 0.02 to 0.30 mg / ml with good repeatability. It may find promising applications in the fields of public health and environment monitoring owing to its simple optics design and applicability in real-time, label-free biodetection.