Wavelength Modulation Surface Plasmon Resonance Research Articles

The investigation of the interaction between fluorescent carbon dots labeling silk fibroin using a fluorescence microscope–surface plasmon resonance system

The use of fluorescent carbon dots (CDs) as highly precise biolabeling probes has been widespread in the fields of live cell imaging and protein labeling due to their small size and excellent photoluminescence ability to accurately target specific molecules with surface chemical properties. However, there was a lack of research on the interaction between CDs and labeled molecules. In this work, we presented a novel investigation strategy, the fluorescence microscopy-surface plasmon resonance (FM-SPR) system, which combined the use of fluorescence microscopy and wavelength modulation surface plasmon resonance to study the interaction between CDs and labeled molecules in real-time. Using this system, simultaneously recorded the SPR signals and the fluorescence images on the surface of the FM-SPR sensor chip. We observed the dynamic curve and fluorescence images of the interaction between green emissive nitrogen-doped carbon dots (N-CDs) and silk fibroin (SF) in real-time. The kinetic parameters, the quantitative analysis, and the investigation of the binding could be achieved. The results showed a strong linear relationship between the change in SPR signals and the concentration of N-CDs, with a linear coefficient of 0.99913. The linear detection range was 2.5 μg/mL–100 μg/mL, and the real lowest detection limit reached 0.5 μg/mL. Additionally, the green fluorescence points in the imaging region on the FM-SPR sensor chip increased with the concentration of N-CDs, which was consistent with the change in SPR signals. Using this system we also acquired the association rate and dissociation rate of N-CDs to SF which were 2.65 × 10−5/s and 1.52 × 10−5/s, respectively. This demonstrated the effectiveness of our method in quantitatively analyzing SF labeled with N-CDs.

Theoretical study of a broadband dual-channel sensor based on sodium-based SPR

For wavelength-modulated surface plasmon resonance (SPR) sensors, bandwidth is an essential factor limiting sensor performance. Wide sensing bandwidth is a prerequisite for a dual-channel sensor with high sensitivity and wide detection range. To improve the performance of the dual-channel sensor, we propose a wide-bandwidth photonic crystal fiber (PCF) sensor based on the sodium-coated SPR effect. The substrate of the proposed sensor is a commercial PCF with air holes arranged in a hexagonal pattern and two planes introduced in the cladding by polishing. A sodium film and Polymethyl methacrylate are deposited in the upper plane to form a refractive index sensing channel. A sodium film and Polydimethylsiloxane are deposited in the lower plane to form a temperature sensing channel. The performance of the sensor was analyzed by the finite element method, and the bandwidth of the sensor covers the wavelength range of 600–1700 nm owing to the low intrinsic loss of the sodium film. Numerical results show that the maximum spectral sensitivity of the sensor is 8700 nm/RIU and 20.20 nm/°C when the refractive index of the analyte is 1.330–1.410, and the temperature is 0–50 °C, respectively. The results also show that the sensitivity of the sensor is insensitive to minor changes in structural parameters. Therefore, the sensor is easy to fabricate. Our study provides a theoretical and analytical basis for preparing sodium-based SPR sensors, which have good prospects for applications in the fields of biochemical detection and environmental monitoring.

Optimization of Surface Plasmon Resonance Biosensor with Ag/Au Multilayer Structure and Fiber-Optic Miniaturization

In this paper, we report a novel wavelength interrogation-based surface plasmon resonance (SPR) system, in which a film of three Ag layers and three Au layers are alternately deposited on a Kretschmann configuration as sensing element. This multilayer film shows higher sensitivity for refractive index (RI) measurement by comparing with single Au layer structure, which is consistent with its theoretical calculation. A sensitivity range of 2056–5893 nm/RIU can be achieved, which is comparable to RI sensitivities of other wavelength-modulated SPR sensors. Compared with Ag film, this Ag/Au multilayer arrangement offers anti-oxidant protection. This SPR biosensor based on a cost-effective Ag/Au multilayer structure is applicable to the real-time detection of specific interactions and dissociation of low protein concentrations. To extend the application of this highly-sensitive metal film device, we integrated this concept on an optical fiber. The range of RI sensitivities with Ag/Au multilayer was 1847–3309 nm/RIU. This miniaturized Ag/Au multilayer-based fiber optic sensor has a broad application in chemical and biological sensing.

An enhanced SPR immunosensing platform for human IgG based on the use of silver nanocubes and carboxy-functionalized graphene oxide

The article describes a wavelength modulation surface plasmon resonance (SPR) biosensor for human IgG. The sensor is based on the use of silver nanocubes (SNCs) and carboxy-functionalized graphene oxide (cGO). The surface of the SNCs was modified with 3-mercaptopropinic acid by silver-thiol chemistry, and this protects the SNCs from oxidation. The cGO possesses abundant carboxy groups that allow high-density immobilization of anti-human IgG on the gold film of the SPR chip. Successful conjugation to the surface was demonstrated by X-ray photoelectron spectroscopy. The SPR biosensor responds to human IgG in the 0.075 to 40 μg mL-1 concentration range. The limit of quantification (LOQ) is smaller by factors of 32, 8 and 4 compared to (a) a conventional sensor, (b) a GO-based sensor, and (c) a cGO-based sensor. The detection scheme presented here offers a versatile and sensitive platform also for determination of other proteins if the corresponding receptors are available.

In situ targeting TEM8 via immune response and polypeptide recognition by wavelength-modulated surface plasmon resonance biosensor.

There is an increasing interest in real-time and in situ monitoring of living cell activities in life science and medicine. This paper reports a whole cell sensing protocol over the interface of Au film coupled in a wavelength-modulated surface plasmon resonance (WMSPR) biosensor. With dual parabolic mirrors integrated in the sensor, the compact and miniaturized instrument shows satisfactory refractive index sensitivity (2220 nm/RIU) and a high resolution of resonance wavelength shift of 0.3 nm to liquid samples. The affinity interactions between the biomarker of human tumor endothelial marker 8 (TEM8) and antibody (Ab) or specific polypeptide (PEP) were firstly introduced to WMSPR biosensor analysis. Both the interaction events of Ab-cell and PEP-cell over the Au film interface can be recognized by the sensor and the balance time of interactions is about 20 min. The concentration range of Ab for quantitative monitoring of the TEM8 expression on human colon carcinoma SW620 cells was investigated. The present low-cost and time-saving method provides a time resolution of binding specificity between Ab/PEP and TEM8 for real-time analysis of antigen on living tumor cell surface.

Studies of gold nanorod-iron oxide nanohybrids for immunoassay based on SPR biosensor

A wavelength modulation surface plasmon resonance (SPR) biosensor based on gold nanorods-Fe3O4 (GNR-Fe3O4) nanohybrids was developed for the determination of mouse IgG. The premade negatively charged Fe3O4 nanoparticles were coated on the surface of positively charged GNRs through electrostatic interaction. The synthetic method was simple, quick and easy operation. The aldehyde group functionalized GNR-Fe3O4 nanohybrids possess unique magnetic property, exceptional optical property and good biocompatibility, which can be used as immobilization matrix for biomolecules. The magnetic nanohybrids can be easily immobilized on the surface of SPR biosensor chip with a magnetic pillar, which simplifies the experimental procedure. The effects of GNR-Fe3O4 nanohybrids on the sensitivity of SPR biosensor were also studied. The SPR biosensor based on GNR-Fe3O4 nanohybrids shows a good response to mouse IgG in the concentration range of 0.15–40.00μgmL−1, while the biosensor based on MPA and Fe3O4 nanoparticles show a good response to mouse IgG in the concentration range of 2.50–40.00μgmL−1 and 1.25–40.00μgmL−1, respectively. As a result, when GNR-Fe3O4 nanohybrids were used in SPR biosensor, the sensitivity for the determination of mouse IgG is significantly enhanced.

Preparation of graphene oxide-based surface plasmon resonance biosensor with Au bipyramid nanoparticles as sensitivity enhancer

A sensitive and selective wavelength-modulation surface plasmon resonance (SPR) biosensor based on graphene oxide (GO) and Au bipyramids (AuBPs) is reported for determination of bovine IgM. GO sheets with lengths of 100–300nm are synthesized and assembled on amine-modified Au film. The large surface area and abundant functional groups of GO allow the efficient immobilization of antibody. AuBPs are nanoparticles with a penta-twinned crystal structure, which have a sharp localized surface plasmon resonance (LSPR) band because of their high monodispersity. In the optimal conditions, the GO-based biosensor with AuBPs as sensitivity enhancers shows a satisfactory response to bovine IgM in the concentration range of 0.03–32μgmL−1. For contrast, traditional biosensor, GO-based biosensor and GO-based biosensor with Au nanorods (AuNRs) as sensitivity enhancers for antigen detection were also investigated. Consequently, the as-prepared GO sheets function as promising support for antibody and GO-based SPR biosensor using AuBPs as enhancers has the highest sensitivity among the four types of biosensors.

Enhanced wavelength modulation SPR biosensor based on gold nanorods for immunoglobulin detection

In this study, gold nanorods (GNRs) and graphene oxide (GO) were used to enhance the sensitivity of wavelength modulation surface plasmon resonance (SPR) biosensor to detect bovine IgG. GNRs were prepared by a method of seed-mediated growth and immobilized on the Au film through 1,6-hexanedithiol by covalent attachment. GO was prepared by a modified Hummers and Offeman's method and can be assembled on the sensor surface through electrostatic interaction with GNRs. Meanwhile, GO was used as a support to immobilize antibody directly. The biosensor based on GNRs/GO sensing membrane exhibits a satisfactory response for bovine IgG in the concentration range of 0.075–40.00µgmL−1. For comparison, the biosensor based on 3-mercaptopropinic acid (MPA) and the biosensor based on GNRs/MPA sensing membrane were also studied for the detection of bovine IgG. The biosensor based on MPA shows a response for bovine IgG in the concentration range of 2.50–40.00µgmL−1. The biosensor based on GNRs/MPA sensing membrane shows a response for bovine IgG in the concentration range of 0.30–40.00µgmL−1. As a result, the biosensor based on GNRs/GO sensing membrane was found to be the most sensitive of the three types of biosensors.

A Novel Graphene Oxide‐Based Surface Plasmon Resonance Biosensor for Immunoassay

Graphene oxide (GO) is used as a support for binding with proteins. A GO-based wavelength modulation surface plasmon resonance biosensor shows high sensitivity and selectivity for detection of human immunoglobulin G (IgG). When IgG is coupled with gold nanorods (AuNRs), the size increase results in a refractive index change.

A protein A modified Au–graphene oxide composite as an enhanced sensing platform for SPR-based immunoassay

A sensitive and selective wavelength modulation surface plasmon resonance (SPR) biosensor is reported with Au nanoparticle decorated graphene oxide (GO) as an enhanced sensing platform. GO sheets possess favourable water dispersibility, good biocompatibility and high loading capacity. An Au-GO composite with the Au spheres size of 15-20 nm was synthesized and modified with staphylococcal protein A (SPA). The as-prepared composite assembles directly onto the Au film surface of the SPR sensor. Meanwhile, SPA specifically recognizes and binds the Fc portion of antibodies, contributing to highly oriented antibody immobilization on the chip surface without any antibody modification. Consequently, the biosensor based on the SPA modified Au-GO composite exhibits a satisfactory response to rabbit IgG in the concentration range of 0.1-50 μg mL(-1), while the biosensor based on the sole SPA layer for antibody immobilization shows a response in the concentration range of 1.6-50 μg mL(-1). Experimental results show that the SPA modified Au-GO composite can be successfully used for the signal amplification of immunosensors, thereby improving the sensitivity and obviating the need of chemical modification of the antibody.

Improved sensitivity of wavelength-modulated surface plasmon resonance biosensor using gold nanorods

In this report, gold nanorods (GNRs) were used to enhance the sensitivity of the wavelength-modulated surface plasmon resonance (SPR) biosensor. The GNRs were designed and fabricated through seed-medicated growth and surface activation by a layer of a weak polyelectrolyte, poly(acrylic acid) for the attaching antibody. Rabbit anti-goat IgG was immobilized on GNRs, and sandwich assays were carried out to detect goat IgG using a wavelength-modulated SPR biosensor. The detection sensitivity of the nanorod-conjugated antibody is 25-100 times more sensitive than the SPR biosensor without GNRs. Drastic sensitivity enhancement, owing to the electromagnetic interaction between the nanotag and the sensing film, was maximized using the longitudinal plasmonic resonance of the GNRs. GNRs could significantly enhance the sensitivity of the SPR biosensor, and the maximum enhancement effect can be achieved when the longitudinal SPR peak wavelength of GNRs functionally matches the surface plasmon wavelength.

Kinetic Analysis of the Interaction between Nonsteroidal Anti‐inflammatory Drugs and Cyclooxygenase‐2 Using Wavelength Modulation Surface Plasmon Resonance

AbstractA surface plasmon resonance (SPR) biosensor based on wavelength modulation technology was developed and validated for the kinetic analysis of the interactions between two nonsteroidal anti‐inflammatory drugs (NSAIDs) and cyclooxygenase‐2 (COX‐2). After the effect of different concentration COX‐2 on the binding capacity of the SPR biosensor surface was studied, the COX‐2 was immobilized covalently onto the biosensor surface using a standard amine coupling method. The affinity constants for indomethacin, ketoprofen binding to COX‐2 are 7.5×103 L/mol and 9.25×103 L/mol, respectively. The biosensor surface can be regenerated after being rinsed with 0.01 mol/L NaOH, and the biosensor can be used repeatedly. These indicated that the wavelength modulation SPR biosensor has the potential application in the fields of pharmacokinetics, pharmacodynamics and drug discovery.

Surface plasmon resonance biosensor based on water-soluble ZnO–Au nanocomposites

A wavelength modulation surface plasmon resonance biosensor based on ZnO–Au nanocomposites for the detection of human IgM was developed. Self-assembly technique has the advantages of flexibility, simplicity and the precise control of film component and was applied to the building of the sensor. The ZnO–Au nanocomposites are in a dumbbell-like shape and can be immobilized on the Au film through 1,6-hexanedithiol by covalent attachment. Meanwhile the activated ZnO nanocrystals can be used to connect protein. The biosensor based on ZnO–Au nanocomposites was used to detect human IgM. Some experimental conditions were examined and optimized. In the selected conditions, the modified biosensor exhibits a satisfactory response for human IgM in the concentration range of 0.30–20.00 μg mL −1. However, the biosensor without ZnO–Au nanocomposites shows a response for human IgM in the concentration range of 1.25–20.00 μg mL −1. Compared with the biosensor based on Au film, when the biosensor based on the ZnO–Au nanocomposites was applied, the sensitivity for determination of human IgM is significantly enhanced.

Sensitivity enhancement of surface plasmon resonance immunosensing by antibody–antigen coupling

A method of the sensitivity enhancement for the wavelength modulation surface plasmon resonance immunosensing is described using an antibody–antigen coupling assay. The sensor surface was prepared by self-assembling monolayer (SAM), and regenerated by rising with citrate buffer. The human factor B (Bf) showed a good response in the concentration range 0.50–20.00 μg/ml in direct assay. However, Bf had a better response in the concentration range 0.05–20.00 μg/ml by using competitive immunoreactions between antibody immobilized on the sensor film and antibody in the solution. When the antibody–antigen coupling assay was used, the lowest concentration of Bf that could be detected is 10-fold lower than by direct assay. With the same antibody–antigen coupling method, fibronectin (FN) could be detected in the concentration range 0.25–20.00 μg/ml. The lowest detectable concentration is eight-fold lower than by direct assay. The sensor chip could be reusable in the determination of antigen for more than 10 assay cycles without significant decrease of the activity.

Study on Interaction of Ginsenosides with Bovine or Human Serum Albumin Using Wavelength Modulation Surface Plasmon Resonance Biosensor

AbstractTo use a newly developed wavelength modulation surface plasmon resonance (SPR) biosensor, an experimental protocol was developed to investigate the interaction of ginsenosides with serum albumin. With a known concentration of the ginsenosides, bound percentages of the ginsenosides with human serum albumin (HSA) or bovine serum albumin (BSA) were obtained. SPR technique could require no labeling and this method provided the detailed information on association and disassociation of molecules in real time. The results indicate that the sensitivity of wavelength modulation SPR biosensor is sufficient for detection and characterization of binding events involving low‐molecular weight compounds and their immobilized protein targets.

Sensitivity enhancement of wavelength modulation surface plasmon resonance biosensor by improving the baseline solution

The sensitivity enhancement of wavelength modulation surface plasmon resonance (SPR) biosensor was described by improving the baseline solution that made the resonant wavelength move to longer wavelength. The baseline solutions here used are ethanol solutions of 1.0%, 2.0%, 4.0% and 6.0%. The higher is the concentration of the ethanol solution, the longer is the resonant wavelength, and the lower is the concentration of the analyte that could be detected. The heat shock protein (Hsp) 70 are studied and when the baseline solutions used are 1.0%, 2.0%, 4.0% and 6.0% ethanol solutions, the lowest concentrations of Hsp 70 that can be detected are 1.00, 0.50, 0.20 and 0.10 μg/ml, respectively.

Characterization of drug-binding levels to serum albumin using a wavelength modulation surface plasmon resonance sensor

The drug binding to serum albumin is an area of intense research in evaluating drug candidates. A simple method based on a wavelength modulation surface plasmon resonance (SPR) sensor was developed for determination of the interaction for a drug and serum albumin. Seven kinds of drugs with different molecular masses and affinities were studied to illustrate the benefits of the wavelength modulation SPR sensor. With a known concentration of a drug, the percentage of the drug binding to human serum albumin (HSA) or bovine serum albumin (BSA) was then determined. The %bound values determined with a SPR sensor were compared with those obtained by other methods. In addition, the reproducibility and stability of the serum albumin immobilized on the sensor surface were studied under the experiment conditions. This method provides detailed information on affinities of the drug binding to serum albumin. The equilibrium constants of reactions for the HSA and penicillin V K, cefoperazone, cefotaximum natricum, oxacillin, amoxicillin, enoxacin, and norfloxacin, were 72.2 ± 3.0, 134 ± 21, 166 ± 25, 261 ± 63, 575 ± 38, 641 ± 36, and 980 ± 16 μmol L −1, respectively, while the equilibrium constants of reactions for the same seven drugs were 112 ± 3.0, 134 ± 19, 161 ± 23, 261 ± 18, 580 ± 85, 558 ± 19, and 675 ± 31 μmol L −1, respectively. The binding percentages range from 90.0 ± 2.2% to 40.8 ± 5.2% for drugs binding HAS, and from 85.9 ± 1.2% to 50.4 ± 2.8% for drugs binding BSA. These results illustrate how the wavelength modulation SPR sensor can be applied to the study of interaction of the small molecular drugs and serum albumin in real time.

Enhanced optical immuosensor based on surface plasmon resonance for determination of transferrin

Wavelength modulation surface plasmon resonance biosensors (SPR) using colloidal Au nanoparticles and double-linker sensing membrane enhancement are reported for determination of transferrin. The 2-mercaptoethylamine (MEA) was immobilized on the biosensor surface with traditional amine coupling method. The interaction between colloidal Au nanoparticles and MEA was investigated. The anti-transferrin was immobilized on the biosensor surface prepared with staphylococcal protein A (SPA). The interaction of the antibody and antigen was monitored in real time. The good response was obtained in the concentration range 1–20, 0.1–20 and 0.05–20 μg/mL for directly immune assay, double-linker assay and colloidal Au-amplified assay. The result clearly demonstrates that these methods may obtain significantly enhancement of sensitivity for the wavelength modulation SPR biosensor.

Sensitivity-enhancement of wavelength-modulation surface plasmon resonance biosensor for human complement factor 4

Sandwich and colloidal Au techniques for enhancing the sensitivity of a wavelength-modulation surface plasmon resonance (SPR) immunosensor are demonstrated by the detection of human complement factor 4 (C4). The design of the wavelength-modulation SPR biosensor is based on fixing the incident angle of light and measuring the reflected intensity of light in the wavelength range spanning 500–900 nm simultaneously. The human C4 had good response in the concentration range 2–20 μg/mL in the direct assay. However, in the sandwich assay, the human C4 had good response in the concentration range 0.2–20 μg/mL and the lowest concentration is 10-fold lower than that obtained by the direct assay. With human C4-Au colloidal conjugate, the human C4 had good response in the concentration range 0.1–20 μg/mL and the lowest concentration is 20-fold lower than that obtained by the direct assay. In the colloidal-Au-enhanced sandwich assay, the human C4 had good response in the concentration range 0.05–5 μg/mL and the lowest concentration is 40-fold lower than that obtained by the direct assay. Under selected experimental conditions, the reproducibility, sensitivity, and reversibility of the enhanced SPR immunoassay are very satisfactory. The results represent potentially significant advantages in the sensitivity of SPR biosensors.

An optical surface plasmon resonance biosensor for determination of tetanus toxin

Surface plasmon resonance (SPR) has been successfully applied for the simple, rapid, and label-free assay of various biomolecules. This assay evaluates a novel wavelength modulation SPR biosensor for the detection of tetanus toxin. The wavelength modulation SPR biosensor is designed based on fixing the incident angle of light and measuring the reflected intensities in the resonance wavelength range spanning 400–800 nm simultaneously. Tetanus toxin (TeNT), one of the most potent toxins known, is synthesized as a 150 kDa single polypeptide chain. The SPR biosensor has been shown to be capable of directly detecting concentration of tetanus toxin as low as 0.028 Lf ml −1. Under selected experimental conditions, the SPR biosensor has a good reproducibility, sensitivity and reversibility. The results illustrate how wavelength modulation SPR biosensor can be used to detect biomolecular interactions.