Change In Resonance Angle Research Articles

E. coli O157:H7 Detection Using Surface Plasmon Resonance Based Biosensor

The detection of foodborne pathogenic bacteria remains a significant challenge, and the need for fast and sensitive detection methods is becoming increasingly important. Escherichia coli is a prevalent bacteria associated with foodborne illness, and this study aimed to evaluate the ability of a surface plasmon resonance (SPR) based biosensor to detect E. coli O157:H7 at low levels in pure culture and artificially contaminated bay leaves (Laurus nobilis) using different injection methods. To develop a biological sensing surface, the sensor surface was functionalized with 3-aminopropyltriethoxysilane (APTES), and polyclonal antibodies were immobilized on the surface for bacteria detection. Bacterial attachment to the antibodies resulted in a change in resonance angle. The biosensor was able to discriminate between cellular concentrations of 103 to 107 CFU/mL and showed potential in detecting different pathogens in various food samples. Before the SPR detection, the sample preparation step was optimized to ensure complex food matrices were suitable for SPR analysis. The results suggest that the SPR based biosensor is a promising tool for the rapid detection of foodborne pathogens in complex food matrices.

Modulating surface plasmon resonance response by an external electromagnetic wave

We fabricated a highly sensitive layered structure of organic molecules and studied the influence of polarization of the external electromagnetic (EM) wave on the surface plasmon resonance response from the layered structure. The layered structure was formed by depositing a self-assembled monolayer (SAM) of mercaptoundecanoic acid (MUA) followed by a single layer of Langmuir-Schaefer (LS) film of traditional calamitic liquid crystal molecule, 4-octyl-4-biphenylcarbonitrile (8CB). The SAM of MUA was found to be non-responsive towards the change in resonance angle (RA) of surface plasmon resonance (SPR) due to the change in polarization of the external EM wave. However, such layer provides a soft-surface platform for the single layer of 8CB molecules which gets perturbed locally due to the incidence of the external EM wave. We obtained an oscillatory modulation of the change in RA due to the change in polarization angle of the EM wave with respect to the plane of incidence. The magnitude of sensitivity was found to be ∼4 milli°/° angle of polarization of the external EM wave. This study strongly suggests that sensitivity of a SPR-based sensor can be controlled by altering the linear state of polarization of the incident external EM wave.

3-D Printed Instrumentation for Point-of-Use Leaky Waveguide Biochemical Sensor

Leaky waveguide (LW) biosensors enable accurate measurements using small sample volumes and are cheap to produce, and hence, are advantageous in the area of point-of-use devices. Yet, current instrumentation to test LW chips is both bulky and costly because of the use of expensive components, such as glass optics, and manufacturing techniques, such as computer numerical control (CNC) machining. Meanwhile, 3-D printing allows the production of complex shapes that cannot be realized using these techniques, while injection molding allows the low-cost production of optical components. 3-D printed instruments offer huge advantages over traditional laboratory instrumentation, in terms of the cost of the manufacturing equipment required, the cost of the resulting instrumentation, size, and portability. This article describes the design and manufacture of a novel 3-D printed biosensor instrument and demonstrates its use for bioanalysis using LWs with a chitosan waveguide layer. This instrument has a refractive index (RI) resolution comparable to laboratory instrumentation and 3-D printed surface plasmon resonance (SPR) instruments [ $2.37\times 10^{-6}$ , $5.90\times 10^{-6}$ , and $1.7\times 10^{-6}$ RI units (RIUs), respectively] and has proven able to detect 133 nM (nmol L−1) levels of immunoglobulin G (IgG) via the measurement of the change in resonance angle produced upon the protein binding to the film.

Modeling of a highly sensitive MoS2-Graphene hybrid based fiber optic SPR biosensor for sensing DNA hybridization

Optical fiber instead of prism is now widely studied in biosensing research. This paper investigates a highly sensitive optical fiber based Ag-MoS2-Graphene hybrid surface plasmon resonance (SPR) biosensor for sensing DNA hybridization. Sensitivity, detection accuracy and quality factor are carefully studied for the performance analysis. Numerical study shows that usingsingle layer of MoS2 in the middle of a Graphene-on-Ag layer, the fiber optic biosensor exhibits high sensitivity of 105.71°/RIU with reasonable detection accuracy and quality factor of 1.626 and 23.23 RIU−1, respectively. This enhanced sensitivity is due to the absorption ability and optical characteristics of graphene biomolecules and high fluorescence quenching ability of MoS2. Numerical investigation also reflects the variation of resonance angle and spectrum of transmitted power for mismatched DNA strands and for complementary DNA strands. These variations are negligible for mismatched DNA strands whereas significantly computable for complementary DNA strands. Thus the proposed sensor effectively differentiates hybridization and single nucleotide polymorphisms (SNP) by examining the level of changes in resonance angle and transmitted power spectrum. Therefore, this fiber optic based Ag-MoS2-Graphene hybrid biosensor might be a promising candidate for the detection of DNA hybridization.

Young’s modulus measurement based on surface plasmon resonance

In this paper, Young’s modulus of polymers is experimentally measured using pressure sensors based on surface plasmon polariton. Theoretical relationships of changes in polymer reflective index due to applying pressure are investigated as well as the dependence of surface plasmon to the polymer reflective index. For the purpose of investigating the effects of the layers thicknesses, numerical simulation is performed using transfer matrix. Changes in resonance angle of surface plasmon due to applying pressure are experimentally studied as well. Practically, a sample of silicon rubber, as one of the most widely-used polymers, is checked and its Young’s modulus is measured as 8.1MPa.

Sensitivity Enhancement of Transition Metal Dichalcogenides/Silicon Nanostructure-based Surface Plasmon Resonance Biosensor.

In this work, we designed a sensitivity-enhanced surface plasmon resonance biosensor structure based on silicon nanosheet and two-dimensional transition metal dichalcogenides. This configuration contains six components: SF10 triangular prism, gold thin film, silicon nanosheet, two-dimensional MoS2/MoSe2/WS2/WSe2 (defined as MX2) layers, biomolecular analyte layer and sensing medium. The minimum reflectivity, sensitivity as well as the Full Width at Half Maximum of SPR curve are systematically examined by using Fresnel equations and the transfer matrix method in the visible and near infrared wavelength range (600 nm to 1024 nm). The variation of the minimum reflectivity and the change in resonance angle as the function of the number of MX2 layers are presented respectively. The results show that silicon nanosheet and MX2 layers can be served as effective light absorption medium. Under resonance conditions, the electrons in these additional dielectric layers can be transferred to the surface of gold thin film. All silicon-MX2 enhanced sensing models show much better performance than that of the conventional sensing scheme where pure Au thin film is used, the highest sensitivity can be achieved by employing 600 nm excitation light wavelength with 35 nm gold thin film and 7 nm thickness silicon nanosheet coated with monolayer WS2.

Sensitivity Enhancement of MoS2 Nanosheet based Surface Plasmon Resonance Biosensor

A surface plasmon resonance based biosensor consisting of SF10 prism, silicon layer, gold thin film and MoS2 enhanced nanosheet is presented. We systematically investigated the SPR reflectivity and resonance angle through the transfer matrix method. Furthermore, with the optimized thickness of gold, silicon and MoS2, we calculated the change of resonance angle to a fixed refractive index change of sample solutions and the full width at half maximum of the reflectivity curves. The excitaition wavelengths of light sources that we use range from 600nm to 1024nm which covers both visible and near infrared light. In addition, the optimum configuration for MoS2-enhanced SPR biosensors are monolayer MoS2 and 7nm silicon layer coated on 50nm Au thin film with 633nm as the excitation wavelength. With these optimized parameters we can efficiently increase the sensitivity by ∼10%. Even without the silicon layers, the pure MoS2 enhanced nanosheet can also improve the sensitivity by ∼8%. The performance of MoS2 enhanced nanosheet is almost 3-fold higher than that of graphene.

Using Surface Plasmon Resonance to Quantitatively Assess Lipid-Protein Interactions.

Surface Plasmon Resonance (SPR) is a quantitative, label-free method for determining molecular interactions in real time. The technology involves fixing a ligand onto a senor chip, measuring a baseline resonance angle, and flowing an analyte in bulk solution over the fixed ligand to measure the subsequent change in resonance angle. The mass of analyte bound to fixed ligand is directly proportional to the resonance angle change and the system is sensitive enough to detect as little as picomolar amounts of analyte in the bulk solution. SPR can be used to determine both the specificity of molecular interactions and the kinetics and affinity of an interaction. This technique has been especially useful in measuring the affinities of lipid-binding proteins to intact liposomes of varying lipid compositions.

Sensitivity enhancement of surface plasmon resonance sensor based on graphene–MoS2 hybrid structure with TiO2–SiO2 composite layer

In this paper, surface plasmon resonance (SPR) sensor based on graphene–MoS2 hybrid structure with composite layer of TiO2–SiO2 is presented. The angular interrogation method is used for the analysis of reflected light from the sensor. For the calculation of the sensitivity, first of all the thicknesses of TiO2, SiO2 and gold layers are optimized for the monolayer graphene and MoS2. Thereafter, at these optimum thicknesses the reflectance curves are plotted for different sensor structure and comparison of change in resonance angle is made among these structures. It is observed that the sensitivity of the graphene–MoS2-based sensor is enhanced by 9.24 % with respect conventional SPR sensor. The sensitivity is further enhanced by including TiO2–SiO2 composite layer between prism base and metal layer and observed that the enhanced sensitivity for this sensor is 12.82 % with respect to conventional SPR sensor and 3.28 % with respect to graphene–MoS2-based SPR sensor. At the end of this paper, the variation of the sensitivity and minimum reflectance is plotted with respect to sensing layer refractive index at the optimum thickness of all the layers and optimum number of MoS2 and graphene layers. It is also observed that four layers of MoS2 and monolayer graphene are best selection for the maximum enhancement of the sensitivity.

Utilization of Chitosan-Based Sensor Thin Films for the Detection of Lead Ion by Surface Plasmon Resonance Optical Sensor

Chitosan-based sensor thin films were fabricated to detect trace amounts of lead ion using surface plasmon resonance (SPR) optical sensor. The gold surface used for SPR measure- ments was modified with chitosan and chitosan-tert-butylcalix[4]arene-tetrakis(N,N-dimethylthioacetamide) (chitosan-BCAT). Both chitosan and chitosan-BCAT layers were deposited on the gold surface by spin coating technique. The experiment has been carried out to monitor the SPR signals for lead ion with sensitive enhancement by chitosan and chitosan-BCAT layers. For both layers, the change in resonance angle (Δθ) is directly proportional to the concentration of lead ion solution. The higher amounts of Δθ were obtained for chitosan-BCAT film due to a specific binding of BCAT with lead ion. The chitosan-BCAT film enhanced the sensitivity of detection down to 0.03 ppm. Data analysis also has been done by Matlab software using Fresnel formula for multilayer system.

Surface Plasmon Resonance Sensor for Supersensitive Detection of Clenbuterol Using Molecularly Imprinted Film

Abstract The supersensitive detection of clenbuterol was achieved by a method of combining molecularly imprinted polymer with surface plasmon resonance in this article. The detection limit of clenbuterol was 1 × 10−15 mol L−1, and the changes in resonance angle (Δθ) had a good linear relationship with the logarithm of clenbuterol concentration in the range from 1 × 10−15–1 × 10−7 mol L−1. Selectivity experiment showed that no Δθ was observed in response to salbutamol until the concentration of 1 × 10−5 mol L−1.

Selective Biorecognition and Preservation of Cell Function on Carbohydrate-Immobilized Phosphorylcholine Polymers

To obtain synthetic materials capable of selectively recognizing proteins and cells, and preserving their functions, biomembrane mimetic polymers having a phospholipid polar group and carbohydrate side chains were designed. Poly[2-methacryloyloxyethyl phosphorylcholine (MPC)-co-n-butyl methacrylate (BMA)-co-2-lactobionamidoethyl methacrylate (LAMA)] (PMBL) was synthesized and coated on substrates by solvent evaporation. Selective binding of galactose-recognized lectin, RCA120, to a PMBL surface was investigated by measurement of surface plasmon resonance. The binding of RCA120 to the PMBL surface was confirmed by a remarkable change in resonance angle. The apparent affinity constant of RCA120 to PMBL3.0 (3.0 mol % LAMA unit in the feed) per LAMA unit was 2.77 x 10(5) M(-1). When a glucose-recognized lectin, concanavalin A, was in contact with PMBL, no change in the resonance angle was observed, and any nonspecific fouling of protein on PMBL was effectively reduced. Cells of the human hepatocellular liver carcinoma cell line (HepG2) having asialoglycoprotein receptors (ASGPRs) were seeded on polymer surfaces. On poly(BMA) (PBMA), many adherent cells were observed and were well-spread with monolayer adhesion, but cell adhesion was reduced on poly(MPC-co-BMA) (PMB). HepG2 adhesion was observed on PMBL because the cell has ASGPRs; the number of cells adhering to the PMBL polymer surfaces increased with an increase in the density of galactose residues on the surface. In contrast, adhesion of NIH-3T3 cells to PMBL was reduced in a manner similar to that on PMB because the NIH-3T3 cells did not have ASGPRs. Cell adhesion to the PMBL surface was well-regulated by ligand-receptor interactions. Furthermore, some of the cells adhering to the PMBL surface had a spheroid form, and similarly shaped spheroids were scattered on the surface. Although poly(BMA-co-LAMA) (PBL) has galactose residues, the adherent cells were spread in a manner similar to those on PBMA. The MPC units in PMBL contribute to make a spheroid formation of HepG2 cells. The amount of albumin secreted from a cell was compared with the chemical structure of the substrate. The spheroid shaped cells cultured on the PMBL surface secreted much more albumin than did the spreading cells that adhered to the PBMA. In conclusion, the biomembrane mimetic carbohydrate-immobilized phosphorylcholine polymers produced a suitable surface for biorecognition and preservation of cell function.

Internally-referenced Resonant Mirror devices for dispersion compensation in chemical sensing and biosensing applications

The Resonant Mirror (RM) Sensor is a leaky planar waveguide optical sensor that uses frustrated total internal re ection (FTR) to couple light into and out of a leaky waveguiding layer. RM modes are dispersive as well as leaky, causing the coupling angle for a particular mode to shift as the illumination wavelength changes. This is a particular problem when using coherent illumination from a laser diode, as these are prone to mode hopping as the diode temperature changes. This leads to sudden changes in the wavelength of the laser output, causing a similar abrupt change in the measured resonance angle. Without some form of referencing, it is impossible to determine whether a change in resonance angle is a result of a wavelength change or a change in surface refractive index.To overcome this problem, an additional buried RM waveguide layer was incorporated into the sensor structure. By using a slightly different thickness for the buried waveguide layer, a second resonance could be obtained for one polarisation which was much less sensitive to surface refractive index changes, but had the same dispersion as the conventional surface RM resonance. As a result, the difference in resonance angle between the buried and surface modes was only sensitive to changes in the refractive index of the overlayer above the surface RM layer. The device is slightly sensitive to changes in temperature, although the response is dominated by the temperature coef®cient of refractive index of the aqueous overlayer. Since the RM layers are very thin( ~1.3 mm in total), thermal equilibrium between the surface and buried modes should be established very rapidly.To demonstrate the utility of this approach, modi®ed RM sensors were fabricated using CVD of silica and silicon nitride. The sensors were tested in two ways; ®rstly by changing the wavelength of illumination using a series of interference ®lters, and secondly by placing materials of different refractive index on the surface of the device. In the ®rst case, the two resonance peaks moved by the same angle, while in the second case, the surface mode moved approximately 25 times further than the buried mode.

FIS activates sequential steps during transcription initiation at a stable RNA promoter.

FIS (factor for inversion stimulation) is a small dimeric DNA-bending protein which both stimulates DNA inversion and activates transcription at stable RNA promoters in Escherichia coli. Both these processes involve the initial formation of a complex nucleoprotein assembly followed by local DNA untwisting at a specific site. We have demonstrated previously that at the tyrT promoter three FIS dimers are required to form a nucleoprotein complex with RNA polymerase. We now show that this complex is structurally dynamic and that FIS, uniquely for a prokaryotic transcriptional activator, facilitates sequential steps in the initiation process, enabling efficient polymerase recruitment, untwisting of DNA at the transcription startpoint and finally the escape of polymerase from the promoter. Activation of all these steps requires that the three FIS dimers bind in helical register. We suggest that FIS acts by stabilizing a DNA microloop whose topology is coupled to the local topological transitions generated during the initiation of transcription.