Surface Plasmon Resonance Angle Research Articles

Evaluation of PVC@Silver Nanocomposite as Sensor for Low Limit Detection of Cadmium Ion By Surface Plasmon Resonance Based Method

AbstractThis study explores the development of a PVC@Silver nanocomposite for enhanced detection of cadmium ions in water samples. Various characterization techniques confirmed the successful incorporation of silver nanoparticles into the polyvinyl chloride (PVC) matrix across different concentrations (1–4%). X-ray diffraction revealed the face-centered cubic crystalline structure of the silver nanoparticles, with the intensities of the (111), (200), (220), and (311) peaks increasing with higher Ag concentrations. The average crystallite sizes ranged from 26.1 nm (3% Ag) to 30.0 nm (2% Ag). Dynamic light scattering showed nanoparticle sizes of 24–43 nm, while zeta potential values of -24 to -40 mV indicated reasonable colloidal stability. Brunauer–Emmett–Teller (BET) surface area analysis demonstrated a decreasing surface area from 30.09 m2/g (1% Ag) to 25.27 m2/g (3% Ag), attributed to pore filling by silver nanostructures. Significantly, the PVC@Silver nanocomposite facilitated sensitive detection of Cd(II) ions using surface plasmon resonance (SPR), exhibiting an SPR angle shift of 26.30° with intensity values ranging from 10.80 (4% Ag) to 12.19 (3% Ag). UV–vis spectra revealed a prominent surface plasmon resonance band at 420–430 nm, indicating the presence of silver nanoparticles. The optical band gap varied from 4.51eV (1% Ag) to 4.12eV (4% Ag).

Tuning optical properties of Au thin film using electric field for surface plasmon resonance biosensor application

The effect of electric field application on the optical properties of gold (Au) thin film for spectroscopic ellipsometry-based surface plasmon resonance (SPR) biosensor applications has been successfully studied. The optical properties, such as the complex refractive index, complex dielectric constant, real optical conductivity, and absorption coefficient, were determined by fitting data from the ψ and Δ functions obtained through measurements using a homemade rotating analyzer ellipsometer. The applied electric fields of 0.8 V/cm, 1.6 V/cm, 2.4 V/cm, and 3.2 V/cm were induced by applying voltages of 1 V, 2 V, 3 V, and 4 V for ellipsometer tests, and 1.6 V/cm to 3.2 V/cm for the SPR test. The Au thin film was deposited onto a glass slide using an evaporator for ellipsometer testing and a BK7 half-cylinder prism was employed for SPR testing. The experimental results show that the real part of the refractive index (n) increases in the spectral range from 1.5 eV to 2.2 eV and from 3 eV to 5 eV and tends to be constant in the range from 2.3 eV to 2.8 eV. Conversely, the imaginary part of the refractive index (k) decreases from 2.8 eV to 3.6 eV and tends to remain consistent from 3.9 eV to 5.0 eV. The dielectric constant (ε1) consistently shows a significant increase within the spectral range of 3 eV–5.0 eV, with a tendency to decrease between 2.1 eV and 2.4 eV. Meanwhile, the imaginary part (ε2) demonstrates an increase in the spectral range of 1.5 eV–2.4 eV and 3.3 eV–5.0 eV while maintaining relatively stable values in the energy spectral range of 2.6 eV–3.0 eV. Moving to the real part of optical conductivity (σ1), it increases within the spectral range from 1.5 eV to 2.4 eV and from 3.5 eV to 5 eV, with relatively constant values between 2.6 eV and 3.1 eV. The absorption coefficient (α) exhibits a decrease in the spectrum between 2.8 eV and 3.6 eV, but the values remain stable within the range of 3.9 eV–5.0 eV. The α slightly decreases in the energy range of 1.8 eV–2.6 eV. The outcomes obtained from these experiments are directly linked to the SPR results, revealing a noticeable shift in the SPR angle (θSPR) of 45.51°, 45.61°, and 45.73° and an increase in the minimum reflectance (Rmin) of 0.05, 0.09, and 0.13 for electric field strengths of 0 V/cm, 1.6 V/cm, and 3.2 V/cm, respectively. These results imply that the application of an external electric field to the surface of the Au thin film disrupts the matching condition between the evanescent wave vector and the surface plasmon wave vector, thereby altering the reflected light under resonance conditions indicated by an increase in the minimum reflectance and SPR angle. This development holds significant promise to further enhance the sensitivity of electro-optic modulation-based biosensors.

Green Synthesis of Magnetite Nanoparticles Using <i>Moringa oleifera</i> and their Electro-Optic Surface Plasmon Resonance Properties

The application of an external electric field to the surface plasmon resonance (SPR) system of green-synthesized magnetite (Fe3O4) nanoparticles (MNPs) is very promising for increasing the SPR detection signal. Electro-optic surface plasmon resonance (EOSPR) behavior of MNPs has been successfully carried out. The EOSPR system was investigated using the Kretschmann configuration with the prism/Au thin film/MNPs/air layer arrangement and applying an electric voltage of 0 V, 2 V, 4 V, and 6 V. In this study, we synthesized MNPs using the green synthesis approach from moringa oleifera extract. The benefits of green synthesis include being safe, affordable, clean, and ecologically friendly processes. X-ray diffraction results obtained crystal size of the MNPs is about 9.2 nm with inverse spinel face-centered cubic crystal structure. Fourier transforms infrared characterization showed the presence of Fe-O bonds at wave numbers 569 cm-1 and 629 cm-1, indicating that MNPs were successfully formed. The saturation magnetization of the samples is 55.3 emu/g. The SPR angle of the SPR system Prism/Au thin film/air without the addition of MNPs is 44.66°. After being deposited by MNPs and induced by a voltage of 0 V, 2 V, 4 V, and 6 V, the SPR angles changed to 44.87°, 44.90°, 44.95° and 45.12°. The addition of MNPs and an external electric field causes the SPR angle to increase. The results of this study can provide new insights into the development of optical devices that can be manipulated electrically and have the potential for future biosensor applications.

Enhancing urine glucose sensing performance through the introduction of two dimensional-transition metal dichalcogenides and gold nanoparticles into silver/UiO-66 chip of surface plasmon resonance

This work presents a high-performance surface plasmon resonance (SPR)-based biosensor for glucose detection. While adding a metal–organic framework layer, UiO-66, to the biosensor improves selectivity and enables direct detection without additional receptors, it does not significantly enhance sensitivity. A SPR-based biosensor is proposed to overcome this limitation by introducing a layer of 2D-transition metal dichalcogenides (2D-TMD) and decorating the UiO-66 structure with gold nanoparticles (UiO-66AuNP). The optical properties of the biosensor for glucose detection in urine are investigated by employing the finite difference time domain (FDTD) method with Kretschmann configuration at a wavelength of 633 nm, and its performance is effectively improved by incorporating 2D-TMD and AuNP layers into the biosensor structure. Notably, the SPR-based biosensor with the decorated UiO-66 layer exhibits a further change in the SPR angle in the presence of glucose-containing urine. Using computational studies, various performance parameters, such as the biosensors’ signal-to-noise ratio and quality factor, are evaluated in addition to sensitivity. The maximum sensitivity achieved is 309.3°/RIU for the BK7/Ag/PtSe2/WSe2/MoS2/UiO-66AuNP/sensing medium structure. The exceptional performance of the proposed biosensor structure demonstrates its suitability for precise glucose detection in urine while also opening new avenues for developing bioreceptor-free SPR-based sensors.

Anti-allergic drug screening in single living mast cells by means of a novel surface plasmon resonance imaging system

In recent years, phenotypic drug screening has achieved renewed prominence, because it can develop drugs for some rare diseases with unknown etiology and without effective therapeutic drugs. Combined with biochip microarray technology, surface plasmon resonance imaging (SPRi) technology based on changes in reflected light intensity has been widely used to analyze interactions between biomolecules, especially for in vitro drug screening. However, changes in reflected light intensity are merely derivative of changes in surface plasmon resonance angles, so current SPRi technology suffers from low accuracy, poor sensitivity, and narrow linear range. In this study, we built an improved SPR microscopic imaging system capable of directly detecting SPR resonance angle (SPR-dip) shifts, with a sensitivity of 8.14 × 10−6 RIU, and a stability less than ± 2 m°. By optimizing the optical path system, the linear correlation coefficient of the system within the scanning range of 3800 m° is 0.9975. Based on this imaging system, we established a reliable screening system for single living mast cell allergy drugs. By developing small molecule microarray chips, we achieved high-throughput screening of 2400 sample points at one time. Our SPR microscopic imaging system integrates the comparative advantages of existing angle-scanning SPRi systems and opens the possibility of new applications in phenotypic drug screening.

Dynamic measurement of an angular Goos–Hänchen shift at a surface plasmon resonance in liquid

We developed a surface plasmon resonance (SPR)-enhanced angular Goos–Hänchen (GH) shift measurement system capable of tracking small refractive index changes with high sensitivity in a liquid environment. Our method can be performed in angular interrogation schemes, where we demonstrate a simple zero-finding algorithm to locate the SPR angle instead of the complicated data processing algorithms used in conventional sensors. We also propose a displacement interrogation scheme for dynamic measurement of small refractive index changes in the sample. The main advantage of our method is the controllability of the measured displacement by standard geometrical optics, allowing measurement sensitivity enhancement without the need to modify the sensor material.

Localized surface plasmon resonance properties dependence of green-synthesized Fe3O4/Ag composite nanoparticles on Ag concentration and an electric field for biosensor application

The use of green-synthesized Fe3O4/Ag composites nanoparticles (NPs) on the surface plasmon resonance (SPR) system induced by the electric field generates the effect of electrooptic-localized surface plasmon resonance (EO-LSPR). EO-LSPR is the promising method to increase dispersibility, generate plasmons, bind to biomolecular targets, modify the refractive index, and increase the SPR signal. Green synthesis of Fe3O4/Ag NPs has several advantages, including being environmentally friendly, cost-effective, and sustainable. This research successfully investigated the EO-LSPR properties of green-synthesized Fe3O4/Ag NPs with various Ag concentrations. Green synthesis of Fe3O4/Ag composites NPs was prepared utilizing Moringa oleifera by an aqueous solution method. The EO-LSPR phenomenon was investigated by applying various voltages in the Kretschmann configuration with a layer arrangement of a prism/Au thin film/NPs/air with a wavelength of 632.8 nm. Transmission electron microscope results show that the average size of Fe3O4/Ag particles is around 16.72 ± 7.30 nm. The scanning electron microscopy-energy dispersive x-ray results showed that Ag was distributed on the surface of Fe3O4. The addition of Ag concentration decreased the saturation magnetization while the coercivity field increased. The SPR angle of the prism/Au thin film/air layer structures is 44.66°. After depositing with Fe3O4/Ag with an Ag concentration of 60 millimolar, the LSPR angle shifted by 0.98°. Under an electric field, the LSPR angle shifted to 1.00°, 1.17°, and 1.22° of 2 volts, 4 volts, and 6 volts, respectively. The results show that applying the electric field induces the LSPR angle of Fe3O4/Ag NPs to shift to a larger angle. Applying an electric field causes a change in the material's refractive index. The greater the applied electric field, the more significant the LSPR angle shifts. The significant shifts in the LSPR angle due to the application of an electric field indicate that the EO-LSPR system using green-synthesized Fe3O4/Ag composites NPs could be a promising alternative to increase the performance of SPR biosensors in the future.

THU048 Determination Of Receptor Binding Affinity Of Growth Hormone Analogues To The Growth Hormone Receptor In A Drug Screening Context

Abstract Disclosure: S. Erlendsson: Employee; Self; Novo Nordisk. Stock Owner; Self; Novo Nordisk. A. Kulakova: Employee; Self; Novo Nordisk. S. Poulsen: Employee; Self; Novo Nordisk. Stock Owner; Self; Novo Nordisk. P. Thygesen: Employee; Self; Novo Nordisk. Stock Owner; Self; Novo Nordisk. Growth hormone (GH) and GH analogues are characterized by their ability to bind and activate the GH receptor (GHR). Binding affinity and functional activity are pivotal parameters for development and characterization of new GH analogues for treatment of growth disorders. The GHR is a member of the class I cytokine family and obtains a tripartite structure consisting of two extracellular fibronectin type III domains (ECD), a single-pass transmembrane domain (TMD), and a disordered intracellular domain (ICD). These receptors lack intrinsic kinase activity but rely on recruitment of intracellular signalling kinases and regulatory proteins. Activation of the downstream JAK-STAT signalling cascade is initiated by formation of an asymmetric GHR dimer induced by binding of GH to the GHR ECDs via two partially overlapping binding sites designated site I and II. The structural rearrangement in the ECDs propagates through the TMD and results in a separation of the ICDs which leads to activation through cross-phosphorylation of the Janus kinases 2 (JAK2). Here we utilize isothermal titration calorimetry (ITC), surface plasmon resonance (SPR) and small angle x-ray scattering (SAXS) to characterize the binding of native GH and GH analogues including somapacitan and pegvisomant to the monomeric GHR as well as an artificial soluble stabilized dimeric GHR. The GH analogues with good binding properties were subsequently tested in vitro for biological activity using a STAT3-luciferase reporter gene assay (RGA) and a proliferation assay with BAF3 cells expressing the human GHR. Both assays were established in two formats enabling testing of both receptor agonists and antagonists. Using SPR we show that the binding of all tested compounds is preserved between the monomeric and dimeric GHR with affinities ranging from near-picomolar to lower micromolar and we are subsequently able to confirm the expected stoichiometry by utilizing a combination of ITC and SAXS. In the RGA and the proliferation assay we demonstrate that a 1:2 stoichiometry is critical for receptor activation regardless of the affinity and therefore we propose high throughput screening of receptor stoichiometry as key in discovery of new growth disorder therapeutics. Presentation: Thursday, June 15, 2023

Genetically encoded phosphatidylserine biosensor for in vitro, ex vivo and in vivo labelling

BackgroundThe dynamics of phosphatidylserine in the plasma membrane is a tightly regulated feature of eukaryotic cells. Phosphatidylserine (PS) is found preferentially in the inner leaflet of the plasma membrane. Disruption of this asymmetry leads to the exposure of phosphatidylserine on the cell surface and is associated with cell death, synaptic pruning, blood clotting and other cellular processes. Due to the role of phosphatidylserine in widespread cellular functions, an efficient phosphatidylserine probe is needed to study them. Currently, a few different phosphatidylserine labelling tools are available; however, these labels have unfavourable signal-to-noise ratios and are difficult to use in tissues due to limited permeability. Their application in living tissue requires injection procedures that damage the tissue and release damage-associated molecular patterns, which in turn stimulates phosphatidylserine exposure.MethodsFor this reason, we developed a novel genetically encoded phosphatidylserine probe based on the C2 domain of the lactadherin (MFG-E8) protein, suitable for labelling exposed phosphatidylserine in various research models. We tested the C2 probe specificity to phosphatidylserine on hybrid bilayer lipid membranes by observing surface plasmon resonance angle shift. Then, we analysed purified fused C2 proteins on different cell culture lines or engineered AAVs encoding C2 probes on tissue cultures after apoptosis induction. For in vivo experiments, neurotropic AAVs were intravenously injected into perinatal mice, and after 2 weeks, brain slices were collected to observe C2-SNAP expression.ResultsThe biophysical analysis revealed the high specificity of the C2 probe for phosphatidylserine. The fused recombinant C2 proteins were suitable for labelling phosphatidylserine on the surface of apoptotic cells in various cell lines. We engineered AAVs and validated them in organotypic brain tissue cultures for non-invasive delivery of the genetically encoded C2 probe and showed that these probes were expressed in the brain in vivo after intravenous AAV delivery to mice.ConclusionsWe have demonstrated that the developed genetically encoded PS biosensor can be utilised in a variety of assays as a two-component system of C2 and C2m2 fusion proteins. This system allows for precise quantification and PS visualisation at directly specified threshold levels, enabling the evaluation of PS exposure in both physiological and cell death processes.

Terahertz Generation by Beating Laser Driven Plasmons in Graphene Embedded Metal Film

A modified ATR configuration, comprising a glass prism embedded by metal film and graphene, is proposed as a suitable nonlinear medium for laser beat wave terahertz generation. Two lasers, launched on the prism at SPR (surface plasmon resonance) angle, get linearly mode converted into surface plasma waves (SPWs) of much higher amplitude. The SPWs exert a beat frequency ponderomotive force on free electrons of metal film and graphene. The ensued nonlinear current drives beat frequency THz plasmons. A surface ripple on graphene or metal assists phase matching and resonantly enhances the THz field amplitude.

Back focal plane imaging for light emission from a tunneling junction in a low-temperature ultrahigh-vacuum scanning tunneling microscope.

We report the design and realization of the back focal plane (BFP) imaging for the light emission from a tunnel junction in a low-temperature ultrahigh-vacuum (UHV) scanning tunneling microscope (STM). To achieve the BFP imaging in a UHV environment, a compact "all-in-one" sample holder is designed and fabricated, which allows us to integrate the sample substrate with the photon collection units that include a hemisphere solid immersion lens and an aspherical collecting lens. Such a specially designed holder enables the characterization of light emission both within and beyond the critical angle and also facilitates the optical alignment inside a UHV chamber. To test the performance of the BFP imaging system, we first measure the photoluminescence from dye-doped polystyrene beads on a thin Ag film. A double-ring pattern is observed in the BFP image, arising from two kinds of emission channels: strong surface plasmon coupled emissions around the surface plasmon resonance angle and weak transmitted fluorescence maximized at the critical angle, respectively. Such an observation also helps to determine the emission angle for each image pixel in the BFP image and, more importantly, proves the feasibility of our BFP imaging system. Furthermore, as a proof-of-principle experiment, electrically driven plasmon emissions are used to demonstrate the capability of the constructed BFP imaging system for STM induced electroluminescence measurements. A single-ring pattern is obtained in the BFP image, which reveals the generation and detection of the leakage radiation from the surface plasmon propagating on the Ag surface. Further analyses of the BFP image provide valuable information on the emission angle of the leakage radiation, the orientation of the radiating dipole, and the plasmon wavevector. The UHV-BFP imaging technique demonstrated here opens new routes for future studies on the angular distributed emission and dipole orientation of individual quantum emitters in UHV.

Investigating the effect of surface termination and thickness of MXene on the detection response of the SPR sensor using FDTD simulation

Surface plasmon resonance (SPR) is an optical-based detection technique that is of great interest in research because of its rapid detection and label-free features. Current SPR sensor development focuses on modifying the sensing surface for maximum bioreceptor and target immobilization. In this research, we proposed SPR sensor with the Kretschmann configuration modified by adding immobilization layers using a few layers of MXene (Ti3C2T2). MXene is an alternative two-dimensional material suitable for sensors because it has surface termination (T2) which active to immobilize the target. The different surface termination (T=O,OH,F) and number of MXene layers was added on the SPR sensor to obtained the optimum parameters of MXene application. Using Finite-Difference Time-Domain (FDTD) method, the SPR sensor is simulated on a different refractive index background which is assumed as the analyte. The different surface termination produces different SPR curves at the same refractive index conditions, the changes are found in the position of the SPR angle and the width of the curve. Thus, the results of surface termination variations are evaluated based on the full-width half-maximum (FWHM) of the curve which indicates the detection accuracy. Meanwhile, the optimum number of MXene layers was evaluated from the sensitivity value of the MXene-modified SPR sensor to changes in refractive index from 1.33 to 1.34. The result shows that the optimum detection performance was obtained from the application of six layers MXene with surface termination F2(Ti3C2F2). This configuration resulted a sensitivity of 150.131°/RIU and the LOD is 0.01633 RIU.

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.

Effects of optic axis rotation on the sensing properties of nematic liquid crystal based surface plasmon resonance (SPR) sensor

The effect of different orientations of the optic axis (OA) in the liquid crystal (LC) UCF-1 in two dimensions on the surface plasmon (SP) mode excited along the surface intermediate between a thin silver film and the LC at different temperatures is theoretically studied using the prism coupling technique and a TM-polarized, monochromatic laser with λ = 5890 Å. The shifts in the surface plasmon resonance (SPR) dip angle at different temperatures for varying alignments of the OA in a plane are determined. Changes in the SPR resonance angles with temperature are found to be significant and linear in a major part of the entire anisotropic phase of UCF-1 for the homeotropic orientation. A linear fit is obtained for the variation of SPR angle of resonance with the molecular order parameter over the entire anisotropic range of UCF-1. The effect of deviations of the OA of the LC from the homeotropic orientation in two dimensions on the temperature sensitivity of the SPR angle of resonance in the linear response temperature range is studied, and its influence on the accuracy of measurement by SPR corresponding to a fixed value of the molecular order parameter is investigated.

Optimization of Surface Plasmon Resonance (SPR) for Gold/Air Interface by using Kretschmann Configuration

The coherent oscillation of electrons at contact among a dielectric and metal when the metal is exposed to incoming plasmon is known as “surface Plasmon resonance”. To achieve the best surface plasmon resonance (SPR) signal, several aspects must be considered, including the excitation wavelength, the sort of metals used, and the thickness of the metal layer. The modification of the surface plasmon resonance (SPR) depending on the thickness of metallic gold was investigated in this study. The reflection spectrum is determined as a function of metal thickness and dielectric medium (air), which is fixed in this case, and measuring the resonance angle for each size (length of the gold layer) to visualize the influence of the metal film on the resonance angle. The analysis concentrated on the impact of gold layer thickness variations on resonance angle shift. SPR's ideal thickness was discovered to be 45-50 nm. We used the spin coating method to create a thin layer. The thickness of thin films is measured by scanning the sample with an atomic force microscope (AFM) tip. The optimum SPR angle profile with the minimum amount of reflection and dip reflection is achieved with this film thickness. The reflectance and resonance angle performance features of gold layers were analyzed utilizing plasmonic Kretschmann configurations at a wavelength nm) in sensing media (air). In an experimental analysis of the improved surface plasmon resonance characteristics of the gold/air coupling, they also showed a significant shift in resonance angle due to the film thickness variation. Biomedical science, optics, biosensing, and medicine are just a few of the domains where the (SPR) has been applied.

S-type fiber surface plasmon resonance strain sensor.

The fiber surface plasmon resonance (SPR) sensor is widely used in high-sensitivity refractive index detection, and there are few reports on SPR sensors used for strain measurement. In this paper, we propose and demonstrate an S-type fiber strain sensor based on SPR. The simulation and testing results indicate that the smaller the vertical axis offset of S-type fiber is, the larger the incidence angle of SPR is, and the closer the working band of SPR is to the shorter wavelength direction. By electrofusion, we fabricated an S-type structure on the single-mode fiber, and by the S-type structure, the high-order cladding mode was excited. A 50 nm gold film was coated on the surface of the fiber cladding behind the S-type structure. The evanescent field of the cladding mode contacted the gold film to produce SPR, and the strain can change the vertical axis offset of the S-type fiber and further change the incidence angle of SPR; hence an S-type fiber strain sensor based on SPR was realized. When the refractive index of the ambient medium is 1.345 RIU, the vertical axis offset and length of the S-shaped structure are 87 and 501 µm, respectively, the resonance wavelength of the fiber SPR strain sensor changes from 648.06 to 631.77 nm with a strain detection range of 0-1200µε, and its sensitivity is -14.38pm/µε. The proposed sensor provides a new solution for the strain measurement of the fiber SPR sensor, which is expected to be used in the fields of engineering, health monitoring, and early warning.

Green Synthesis of Fe3O4/Chitosan Nanoparticles Utilizing Moringa Oleifera Extracts and Their Surface Plasmon Resonance Properties

In this study, a simple, rapid, and environmentally friendly green approach for synthesizing Fe3O4 and Fe3O4/chitosan nanoparticles with various concentrations was developed. The nanoparticles had a spherical shape with a cubic inverse spinel structure. The functionalization of the Fe3O4 nanoparticles using chitosan increased the crystallite size of the nanoparticles from 7.2 to 7.8 nm. The Fourier transform infrared spectra of the Fe3O4/chitosan nanoparticles showed the existence of the characteristic peaks of chitosan in addition to a peak at 578 cm−1, which corresponds to the stretching of the Fe−O group. The UV-visible spectra demonstrated a wide absorption band with the appearance of small peaks of chitosan absorption at 205 and 215 nm. The saturation magnetization of the Fe3O4 was 54.1 emu g−1. The surface plasmon resonance (SPR) measurements showed an enhancement in the SPR angle as the ratio of chitosan to Fe3O4 increased, wherein the angle shift from 0.17° to 1.91°. The chitosan covering the Fe3O4 nanoparticle surface caused the refractive index to change, which increased the SPR angle shift. The obtained results indicated that the SPR properties of the Fe3O4 nanoparticles were significantly improved by modification with chitosan. These results also indicated that the use of chitosan in Fe3O4 nanoparticles can enhance SPR properties, which has potential for future SPR-based sensor applications.

A label-free SPR biosensor for specific detection of TLR4 expression; introducing of 10-HDA as an antagonist

Toll-like receptor 4 (TLR4) is actively involved in many health-related problems, including transplantation rejection and autoimmune diseases. Therefore, it is important to identify an antagonist to inhibit the TLR4-induced immune cell activation. In our previous study, 10-hydroxy-2-decanoic acid (10-HDA) was introduced as a potential antagonist for TLR4; however, possible interaction between 10-HDA and TLR4 needed to be detected. Due to the ability of surface plasmon resonance (SPR) biosensor to confirm the specific interactions between receptors and ligands, a new configuration of SPR biosensor proposed to detect the possible interaction between 10-HDA and TLR4. Hence, 10-HDA was immobilized using the (3-aminopropyl) triethoxysilane (APTES) polymer as a crosslinking agent on the Ag-MgF2 surface. Besides, genetically modified HEK293T cells with high TLR4 expression were used to study the possible interaction between 10-HDA and TLR4. Surprisingly, the SPR angle was significantly reduced in the presence of HEK cells expressing TLR4, while HEK cells without TLR4 did not affect the SPR angle. So, the proposed SPR biosensor successfully detected the interaction betweenTLR4 and 10-HDA. The sensitivity and detection limit of the biosensor were achieved at 0.05 and 0.5 million cells expressing TLR4, respectively, with a two-fold dynamic range.

An optical sensor combining surface plasmon resonance, light extinction, and near-critical angle reflection, for thin liquid film biochemical sensing

We present a novel and low-cost optical sensor to obtain at the same time, fast and label-free optical information such as reflectivity, refractive index and extinction coefficient of biochemical samples. The sensor measures in around one minute optical internal reflectivity as a function of the angle of incidence at the interface between a glass prism covered by a gold nanofilm (≈20 nm) in contact with a liquid sample (≈10 µL). The nanofilm is thin enough that a large fraction of the incident light transmits through it at angles of incidence below the critical angle set by the prism and sample refractive indices (≈ 61°), but thick enough to present a Surface Plasmon Resonance dip for angles of incidence beyond that critical angle. The calculated sensitivity of SPR to the surface refractive index is 168.35 deg/RIU. We demonstrate that when a sample contains live bacteria (E. coli) the whole reflectivity curve including the SPR region is clearly affected, and to adjust a theoretical model to the experimental curves, it is necessary to assume a complex refractive index of the nanofilm appreciably different than that of gold. The optical curve of the sensor provides more information than a conventional SPR measurements offering a more complete strategy for the analysis of biochemical substances and bacterial cell suspensions.

Microstructural and Surface Plasmon Resonance Properties of Green-Synthesized Ag Nanoparticles Using <i>Moringa oleifera</i> Extract

Ag nanoparticles (NPs) have been successfully synthesized by the green synthesis method using Moringaoleifera (MO) extract with various incubation times (24 and 48 hours) as an active material for surface plasmon resonance (SPR) biosensor. Transmission electron microscopy analysis indicated the formation of spherical particles with an average crystal size of 29 nm. Selected area electron diffraction confirmed that Ag NPs is face-centered cubic (FCC) crystal structure. Fourier-transform infrared measurements show the band at 3330 cm-1, 2067 cm-1, 1634 cm-1 for an incubation time of 24 hours and 3328 cm-1, 2063 cm-1, 1633 cm-1 for an incubation time of 48 hours. The results prove the proteins and phenolics compound present in the MO extract responsible as reducing agents. The maximum absorption of the green-synthesized Ag NPs in the UV-Vis spectra shows the SPR band at 326 nm and 328 nm for an incubation time of 24 and 48 hours, respectively, and absorption intensity decrease with the increase of incubation time. The result shows the SPR angle shifted to the larger angle of incident light by using green-synthesized Ag NPs. However, the increased incubation time affects the angle shift to the lower angle of the SPR shift. The addition of the green-synthesized Ag NPs leads to enhance the sensitivity of the SPR biosensor.