Wavelength-interrogated Surface Plasmon Resonance Research Articles

Enhancing Precision in Fuel Adulteration Detection: Utilizing a Wavelength Interrogation Surface Plasmon Resonance Approach

Enhancing Precision in Fuel Adulteration Detection: Utilizing a Wavelength Interrogation Surface Plasmon Resonance Approach

Quasi-phase extraction-based surface plasmon resonance imaging method for coffee ring effect monitoring and biosensing.

Wavelength interrogation surface plasmon resonance imaging (WSPRi) sensing has unique advantages in high-throughput imaging detection. The refractive index resolution (RIR) of WSPRi is limited to the order of 10-6 RIU. This paper demonstrates a novel WSPRi sensing system with a wavelength scanning device of an acousto-optic tunable filter (AOTF) and a low-cost speckle-free SPR excitation source of a halogen lamp. We developed a sensitive quasi-phase extraction method for data processing. The new technique achieved an RIR of 8.84×10-7 RIU, which is the first WSPRi system that has an RIR in the order of 10-7 RIU. Moreover, we performed a real-time recording of the formation of the coffee ring effect during brine evaporation and enhanced the biosensor performance of SPR for the first time. We believe the higher RIR and accuracy of the system will benefit more potential applications toward exploring the biomolecules' behaviors in biological and biochemistry studies.

Spectrometer-based wavelength interrogation SPR imaging via Hadamard transform.

We present spectrometer-based wavelength interrogation surface plasmon resonance imaging (SPRi) without mechanical scanning. A polarized broadband light source illuminates an object via a gold-coated prism; the reflected light is spatially modulated by a digital mirror device (DMD) and then measured with a spectrometer. Reflectance spectral images are reconstructed via the Hadamard transform (HT), and a refractive index (RI) map is visualized from the reflectance spectral images by analyzing the resonance peak shift of the spectrum at each image pixel. We demonstrate the feasibility of our method by evaluating the resolution, sensitivity, and dynamic detection range, experimentally obtained as ∼2.203 × 10-6 RI unit (RIU), ∼3,407 nm/RIU, and ∼0.1403 RIU, respectively. Furthermore, simulations are performed to validate the experimental results.

Effect of Spectral Signal-to-Noise Ratio on Resolution Enhancement at Surface Plasmon Resonance.

Refractive index resolution is an important indicator for a wavelength interrogation surface plasmon resonance sensor, which can be affected by signal-to-noise ratio. This paper investigates the impact of spectral signal-to-noise ratio on a surface plasmon resonance sensor. The effects of different spectral powers and noises are compared and verified through simulation and experiments. The results indicate that the optimal resonance wavelength is changed and the refractive index resolution can even be nearly twice as good when the spectral signal-to-noise ratio is increased. The optimal resonance wavelength can be found by changing the spectral power distribution or noise.

High-throughput imaging surface plasmon resonance biosensing based on ultrafast two-point spectral-dip tracking scheme

Wavelength interrogation surface plasmon resonance imaging (λSPRi) has potential in detecting 2-dimensional (2D) sensor array sites, but the resonance wavelength imaging rate limits the application of detecting biomolecular binding process in real time. In this paper, we have successfully demonstrated an ultrafast λSPRi biosensor system. The key feature is a two-point tracking algorithm that drives the liquid crystal tunable filter (LCTF) to achieve fast-tracking of the resonance wavelength movement caused by the binding of target molecules with the probe molecules on the sensing surface. The resonance wavelength measurement time is within 0.25s. To date, this is the fastest speed ever reported in λSPRi. Experiment results show that the sensitivity and dynamic are 2.4 × 10-6 RIU and 4.6 × 10-2 RIU, respectively. In addition, we have also demonstrated that the system has the capability of performing fast high-throughput detection of biomolecular interactions, which confirms that this fast real-time detecting approach is most suitable for high-throughput and label-free biosensing applications.

The capture of antibodies by antibody-binding proteins for ABO blood typing using SPR imaging-based sensing technology

In this study, a wavelength-interrogated surface plasmon resonance imaging-based immunosensor was developed for ABO blood typing. To construct the immunosensor, the detection line array was formed by the site-directed immobilization of blood group antibodies on SPR chip modified with antibody-binding proteins. Red blood cell (RBC) samples were flowed into the multichannel flow cell that was orthogonal to the detection line arrays. By serially analyzing the interaction between RBCs, antibody A, and antibody B through the observed changes in the resonance dip, blood typing of four RBC samples was achieved in a single run. Detailed investigations focused on optimizing the conditions that affected the efficiency and sensitivity of immunoassay. Under the optimized conditions, the RBC samples were appropriately grouped in less than 1 h, including chip modification time. The lowest detection limit for RBC-A and RBC-B was 2×106 cells/ml. The immunosensor developed through this study provided a simple, rapid, high-throughput, and sensitive immunology strategy for classification of ABO blood group.

Surface plasmon resonance sensing with adjustable sensitivity based on a flexible liquid core coupling unit

The signal amplification methods of surface plasmon resonance (SPR) are mainly with sample selectivity. Herein proposed is a liquid core coupling SPR sensing method with adjustable sensitivity and universal applicability. A liquid core coupling unit and based on which a wavelength interrogation SPR sensor have been designed and constructed, in which a conventional chip could be used with an ingenious design and the sensitivity can be adjusted by changing the liquid core refractive index. The experimental data revealed that the sensitivity can be enhanced for 7.8 times by decreasing the liquid core refractive index from 1.5174 to 1.4502. The real applicability was validated by determination of carcinoembryonic antigen (CEA) with the signal intensity of the early stage colon cancer patient clearly up-regulated for nearly 18 folds compared with the healthy. It exhibited an adequate sensitivity, and further considering its simplicity avoiding the troublesome analysis process and/or chip preparing procedure, and extendibility to SPR imaging, the proposed method would be promising for medical diagnostics, food safety, environmental monitoring, and so on.

Nanoporous Gold Films Prepared by a Combination of Sputtering and Dealloying for Trace Detection of Benzo[a]pyrene Based on Surface Plasmon Resonance Spectroscopy.

A wavelength-interrogated surface plasmon resonance (SPR) sensor based on a nanoporous gold (NPG) film has been fabricated for the sensitive detection of trace quantities of benzo[a]pyrene (BaP) in water. The large-area uniform NPG film was prepared by a two-step process that includes sputtering deposition of a 60-nm-thick AuAg alloy film on a glass substrate and chemical dealloying of the alloy film in nitric acid. For SPR sensor applications, the NPG film plays the dual roles of analyte enrichment and supporting surface plasmon waves, which leads to sensitivity enhancement. In this work, the as-prepared NPG film was first modified with 1-dodecanethiol molecules to make the film hydrophobic so as to improve BaP enrichment from water via hydrophobic interactions. The SPR sensor with the hydrophobic NPG film enables one to detect BaP at concentrations as low as 1 nmol·L−1. In response to this concentration of BaP the sensor produced a resonance-wavelength shift of ΔλR = 2.22 nm. After the NPG film was functionalized with mouse monoclonal IgG1 that is the antibody against BaP, the sensor’s sensitivity was further improved and the BaP detection limit decreased further down to 5 pmol·L−1 (the corresponding ΔλR = 1.77 nm). In contrast, the conventional SPR sensor with an antibody-functionalized dense gold film can give a response of merely ΔλR = 0.9 nm for 100 pmol·L−1 BaP.

Single chip SPR and fluorescent ELISA assay of prostate specific antigen.

A multi-channel system combining fluidics and micropatterned plasmonic materials with wavelength interrogation surface plasmon resonance (SPR) and fluorescence detection was integrated from the combination of a small and motorized fluorescence microscope mounted on a portable 4-channel SPR instrument. The SPR and fluorescent measurements were performed based on the same detection area in a multi-channel fluidic, with a sensing scheme for prostate-specific antigen (PSA) consisting of a sandwich assay with a capture anti-PSA immobilized onto the SPR sensor and a detection anti-PSA modified with horseradish peroxidase (HRP). In this dual-detection instrument, fluorescence was measured from the solution side of the micropatterned gold film, while the interface between the glass prism and the gold film served to interrogate the SPR response. The SPR sensors were comprised of microhole arrays fabricated by photolithography to enhance the instrumental response for PSA detection by approximately a factor of 2 to 3 and they were coated with a self-assembled monolayer of a peptide (3-MPA-HHHDD-OH) to minimize nonspecific adsorption. PSA was successfully detected at clinical concentrations from 10 pM to 50 nM with this integrated system in a single assay lasting 12 minutes, almost centering on the desired range for PSA diagnostic tests (>4 ng mL(-1) or >150 pM). The combination of two robust techniques in a single chip and instrument has led to a simple and effective assay that can be carried out on a small and portable instrument providing rapid biodetection of an important cancer biomarker with a dynamic range of nearly 4 orders of magnitude in the clinical range.

Label-free detection of biotin using nanoporous TiO2/DNA thin-film coated wavelength interrogated surface plasmon resonance sensors

The sensing sensitivity of the wavelength interrogated surface plasmon resonance(WISPR) biosensor could be improved by self-assembly of nanoporous thin-film of TiO2 nanoparticles/DNA(TiO2/DNA) n (n is the number of bilayer) on wavelength interrogated surface plasmon resonance(WISPR) chips. The growth behavior and surface structure of the nanoporous thin-film were investigated by UV-Vis spectroscopy and scanning electron microscopy, respectively. The home-made WISPR sensor with Krestchmann configuration consisted of a tungsten-halogen lamp as a photon source and a CCD camera as the detector. After the deposition of (DNA/TiO2) n thin film on WISPR chips, the resonance peak of the reflection spectra appeared in air. With the increases of n, the resonance wavelength gradually red shifted, which is consistent with the simulated results. After the optimization of the porous film, the WISPR biosensor was utilized to detect low-molecular-weight analytes, such as biotin. The result demonstrates that the sensitivity of [poly(styrene sulfonate)/polyally lamine hydrochlorides]5(PSS/PAH)5 could be 4 times higher than that of polyelectrolyte multilayer modified WISPR sensor.

Wavelength-Interrogated Surface Plasmon Resonance Sensor Based on Au-Ag Alloy Film

An Au-Ag alloy film surface plasmon resonance (SPR) sensor was studied experimentally and theoretically. SPR chips were prepared by sputtering a glass surface with a 50-nm-thick Au-Ag alloy film, and experiments were carried out with the wavelength-interrogated SPR sensor using the Kretschmann configuration. Aqueous sodium chloride and bovine serum albumin solutions were used to study the refractive index and adsorption sensitivities of the sensor. The results were compared with those obtained using Au film andAg film SPR sensors. The refractive index sensitivity of theAu-Ag alloy film SPR sensor is higher than that of the Au film SPR sensor, but lower than that of the Ag film SPR sensor. The adsorption sensitivity of the Au- Ag alloy film SPR sensor is similar to that of the Ag film SPR, and three times of the Au film SPR sensor. Theoretical studies showed that that the sensitivity of theAu-Ag alloy film SPR is close to that of theAg film SPR sensor, and 2.31 times of the Au film SPR sensor. The full width at half maximum of the Au-Ag film sensor is

In situ molecular self-assembly and sensitive label-free detection of streptavidin via a wavelength interrogated surface plasmon resonance sensor

The sensing sensitivity of wavelength interrogated surface plasmon resonance(WISPR) biosensor is improved by self-assembly of polyelectrolyte multilayer(PEM) film of poly(allylamine hydrochloride)(PAH)/poly(sodium-p-styrenesulfonate)(PSS) on the Au film coated glass chip via the layer-by-layer(LBL) technique. The home-made WISPR with Krestchmann configuration consists of a tungsten-halogen lamp as a photon source and a charge coupled device(CCD) camera as the detector. The influence of PEM film thickness on the optical properties of WISPR biosensors was investigated theoretically and experimentally. In order to achieve higher sensing sensitivity, the PEM film thickness has to be designed as ca.14 nm at an Au layer thickness of 50 nm and an incidental angle of 11.8°. Furthermore, the PEM coated WISPR biosensor can serve as highly sensitive biosensor, in which the biotin-streptavidin is used as bioconjugate pair. After deposition of the PEM film of (biotin/PAH)(PSS/PAH)3, the modified WISPR biosensor is more sensitive to the low concentration(<0.01 mg/mL) of streptavidin. And the sensing sensitivity can be further increased by one order of magnitude compared with that of the biotin/PAH coated WISPR biosensor. Thus, such low-cost, high-performance and efficient PEM-coated WISPR biosensors have great potentials in a diverse array of fields such as medical diagnostics, drug screening, food safety analysis, environmental monitoring, and homeland security.

Polarization-interferometry-based wavelength-interrogation surface plasmon resonance imager for analysis of microarrays

Polarization interferometry (PI) techniques, which are able to improve surface plasmon resonance (SPR) sensing performance and reduce restrictions on allowable parameters of SPR-supporting metal films, have been experimentally realized only in SPR sensors using monochromatic light as a source. Wavelength-interrogation SPR sensors modulated by PI techniques have not been reported due to the wavelength-sensitive characterization of PI phase compensators. In this work we develop a specially designed rhombic prism for phase compensating which is totally insensitive to wavelength. For the first time we successfully apply PI technique to a wavelength-interrogation SPR imager. This imager is able to offer two-dimensional imaging of the whole array plane. As a result of PI modulation, resolutions of 1.3×10(-6) refractive index unit (RIU) under the normal condition and 3.9×10(-7) RIU under a more time-consuming condition are acquired. The application of this imager was demonstrated by reading microarrays for identification of bacteria, and SPR results were confirmed by means of fluorescence imaging.

Wavelength-interrogated surface plasmon resonance sensor with mesoporous-silica-film-enhanced sensitivity to small molecules

Sol-gel copolymer-templated mesoporous silica films with a thickness of 70 nm and interpore spacing of 4.34 nm were fabricated on gold layer covered glass substrates for application as a wavelength-interrogated surface plasmon resonance (SPR) sensor. The resonance wavelength (λ(R)) of the sensor with a solution sample was determined by absorptiometry at a given incident angle. A comparison between the experimental data obtained with the coated and uncoated SPR chips demonstrated that the mesoporous silica film effectively enhanced sensor response to individual adsorption of cysteamine molecules and lead(II) ions. An approximate proportional relationship between the resonance-wavelength shift of the sensor and the volume fraction of analyte molecules adsorbed in the mesoporous silica film was obtained by numerical simulation. Porosities of 0.865 and 0.785 for the two silica films used as well as the volume fractions of 0.048 and 0.116 for adsorbed lysozyme and cysteamine molecules were determined by fitting the simulation results to the experimental data. The adsorbed amount of cysteamine (∼0.5 nm) is equivalent to more than 16 full monolayers on the geometric surface of the mesoporous silica film used. In contrast, an equivalence of less than 2 full monolayers for adsorbed lysozyme molecules (3 nm × 3 nm × 4.5 nm) suggests that the mesoporous silica film has good size-selective adsorption capability due to its uniform pore size distribution. Cysteamine modification of the mesoporous silica film renders the SPR sensor able to detect lead(II) ions at concentrations as low as 1 nM.

High-resolution surface plasmon resonance sensors based on a dove prism

Wavelength interrogation surface plasmon resonance (SPR) spectroscopy using a dove prism combines a simple and inexpensive optical design with high-resolution refractive index monitoring and biosensing. A BK7 dove prism inverts an optical image with a total internal reflection angle of 72.8°, an angle active in SPR. Hence, a unique system can accomplish SPR biosensing using wavelength interrogation and also perform SPR imaging. This optical configuration advantageously uses a single axis optical path between each optical component, simplifying the optical design of SPR instruments without compromise of the analytical performance. Fluidics were also incorporated to the instrument design for efficient sample delivery. The SPR instrument is characterized in terms of refractive index (RI) sensitivity, RI resolution, reproducibility, and application for monitoring low concentration biological events. Data analysis methodologies are compared for improved resolution of the measured response. Raw data analyzed using a minimum hunting procedure results in RI resolution in the 10 −6 range, while pre-treating data with singular value decomposition improves the resolution by one order of magnitude. Depending on the spectrophotometer employed, the RI range accessible can be easily tuned; examples with a 550–850 nm and a 550–1100 nm spectrophotometers are shown and results respectively in RI ranges of 1.32–1.39 RIU and 1.32–1.42 RIU. Monitoring of μM concentration of β-lactamase is performed using the wavelength interrogation configuration of the biosensor. Finally, a SPR image of a surface with a water droplet (volume = 500 nL) was obtained using the dove prism SPR with a band pass filter and a CCD camera. SPR using a dove prism configuration combines advantages of portable SPR instruments, SPR imagers and research-grade SPR instruments in a unique platform.

Optimizing Surface-Plasmon Resonance Sensors for Limit of Detection Based on a Cramer–Rao Bound

This paper addresses the optimization of prism-coupled, wavelength-interrogated surface-plasmon resonance (SPR) sensors. Limit of detection (LOD), rather than sensitivity, is chosen as a figure of merit. The Cramer-Rao bound (CRB) for spectral shift estimation allows lower bounds to be placed on LOD independent of interrogation system and estimation algorithm. Analytic evaluation of the CRB for a Lorentzian spectral feature justifies common observations about the relationship between resonance line shape and sensor performance. Numerical evaluation of standard SPR sensor configurations shows that maximizing sensitivity is an insufficient criterion for minimizing limit of detection. Designs optimized for LOD are presented for common SPR sensor materials and geometries.

DETECTION OF METAL IONS USING A WAVELENGTH INTERROGATION SURFACE PLASMON RESONANCE SENSOR WITH CALIX[4]ARENE DERIVATIVES AS SENSING FILMS

A wavelength interrogation surface plasmon resonance (SPR) sensor with gold substrate modified with calix[4]arene derivative as sensing film was used to detect metal ions in aqueous solutions. We found that only Ag+and Cu2+could be selectively detected with the detection limit of 10−7 mol/L and 10−4 mol/L, respectively. XPS data confirmed the presence of Au-S bond between the calixarene derivative and the gold substrate and complexation between the calixarene derivative and Ag+ or Cu2+.

Contents volume 38 (1989)

In this study, a wavelength-interrogated surface plasmon resonance imaging-based immunosensor was developed for ABO blood typing. To construct the immunosensor, the detection line array was formed by the site-directed immobilization of blood group antibodies on SPR chip modified with antibody-binding proteins. Red blood cell (RBC) samples were flowed into the multichannel flow cell that was orthogonal to the detection line arrays. By serially analyzing the interaction between RBCs, antibody A, and antibody B through the observed changes in the resonance dip, blood typing of four RBC samples was achieved in a single run. Detailed investigations focused on optimizing the conditions that affected the efficiency and sensitivity of immunoassay. Under the optimized conditions, the RBC samples were appropriately grouped in less than 1 h, including chip modification time. The lowest detection limit for RBC-A and RBC-B was 2×106 cells/ml. The immunosensor developed through this study provided a simple, rapid, high-throughput, and sensitive immunology strategy for classification of ABO blood group.