Surface Plasmon Resonance Reflectance Curves Research Articles

Influence of the configuration of metal sensing layers on the performance of a bimetallic (Ag–Cu) surface plasmon resonance biosensor

Bimetallic surface plasmon resonance (SPR) sensors have the potential to overcome the drawbacks of individual metals, but the effect of the configuration of the two metallic layers on the performance of the sensors has not been explored. This study examines the influence of different positions of a thin layer of silver in relation to a copper layer on the sensitivity of such a bimetallic SPR sensor. The design of this configuration aims to improve the SPR reflectance curve and strengthen the evanescent electric field to improve the sensor efficiency. Our findings indicate that, by optimizing the architectures of SPR sensors and using a silver–copper bimetallic structure, we can achieve superior performance compared to devices that utilize only silver or copper. The optimized Ag (5 nm)/Cu (55 nm) sensor design, with the best sensitivity of 299.09° RIU−1, can detect a change of 0.43°/(g dl−1) for hemoglobin in blood, 0.35°/(g dl−1) for glucose in urine, and 0.1°/(%) for methanol in ethanol. We also demonstrate the importance of signal quality by introducing two new parameters that offer a better quantitative indication of the efficiency of a sensor than is obtained by using only sensitivity.

Exploitation of SnO2/Polypyrrole Interface for Detection of Ammonia Vapors Using Conductometric and Optical Techniques: A Theoretical and Experimental Analysis.

This study describes the construction of a lab-built Surface Plasmon Resonance (SPR) system for gas sensing applications employing a highly sensitive and trustworthy optical approach. The nanocomposite thin film of tin oxide (SnO2) and Polypyrrole (PPy) were prepared for sensing highly toxic gas, i.e., ammonia (NH3) gas. The gas sensor was validated by both optical and conductometric techniques of gas sensing. The optical SPR gas sensor is based on the change in refractive index at the SnO2/Polypyrrole (PPy) interface with gas adsorption (NH3). The thickness of SnO2 and Polypyrrole thin films was optimised using theoretical calculations for a sharp SPR reflectance curve. The manuscript also offers theoretical SPR curves for different PPy and SnO2 layer thicknesses. To support the theoretical conclusions, the effects of NH3 gas on the prism/Au/SnO2/Polypyrrole system were also investigated experimentally. In comparison to other research described in the literature, it was observed that the constructed sensor’s sensitivity was higher. The obtained results demonstrate the utility of the SPR setup in the investigation of the interactions of adhered gas molecules with dielectrics and gas sensing. For conductometric gas sensing studies, the film having optimised thicknesses for sharp SPR reflectance curves was separately prepared on Interdigitated Electrodes. At a low working temperature of roughly 150 °C, the sensing response of the constructed film was observed and found to be maximal (60).

Direct and Sensitive Detection of Dopamine Using Carbon Quantum Dots Based Refractive Index Surface Plasmon Resonance Sensor.

Abnormality of dopamine (DA), a vital neurotransmitter in the brain’s neuronal pathways, causes several neurological diseases. Rapid and sensitive sensors for DA detection are required for early diagnosis of such disorders. Herein, a carbon quantum dot (CQD)-based refractive index surface plasmon resonance (SPR) sensor was designed. The sensor performance was evaluated for various concentrations of DA. Increasing DA levels yielded blue-shifted SPR dips. The experimental findings revealed an excellent sensitivity response of 0.138°/pM in a linear range from 0.001 to 100 pM and a high binding affinity of 6.234 TM−1. The effects of varied concentrations of DA on the optical characteristics of CQD thin film were further proved theoretically. Increased DA levels decreased the thickness and real part of the refractive index of CQD film, according to fitting results. Furthermore, the observed reduction in surface roughness using AFM demonstrated that DA was bound to the sensor layer. This, in turn, explained the blue shift in SPR reflectance curves. This optical sensor offers great potential as a trustworthy solution for direct measurement due to its simple construction, high sensitivity, and other sensing features.

Cellulose and Vanadium Plasmonic Sensor to Measure Ni2+ Ions

A novel vanadium–cellulose composite thin film-based on angular interrogation surface plasmon resonance (SPR) sensor for ppb-level detection of Ni(II) ion was developed. Experimental results show that the sensor has a linear response to the Ni(II) ion concentrations in the range of 2–50 ppb with a determination coefficient (R2) of 0.9910. This SPR sensor can attain a maximum sensitivity (0.068° ppb−1), binding affinity constant (1.819 × 106 M−1), detection accuracy (0.3034 degree−1), and signal-to-noise-ratio (0.0276) for Ni(II) ion detection. The optical properties of thin-film targeting Ni(II) ions in different concentrations were obtained by fitting the SPR reflectance curves using the WinSpall program. All in all, the proposed Au/MPA/V–CNCs–CTA thin-film-based surface plasmon resonance sensor exhibits better sensing performance than the previous film-based sensor and demonstrates a wide and promising technology candidate for environmental monitoring applications in the future.

Performance analysis of graphene-based surface plasmon resonance biosensor for blood glucose and gas detection

The present study exhibits excellent sensing characteristics of graphene-based prism-coupled surface plasmon resonance (SPR) biosensor for effectual sensing of both glucose concentrations in human blood samples in the range 25–175 mg/dl and gas with refractive index variations from 1.0000 to 1.0007 at a wavelength of 589 nm. The foremost attractiveness of the proposed SPR biosensor lies with excellent optical properties of N-FK51A-based glass prism along with the inclusion of a gold layer and a thin graphene layer. Transfer matrix method and angular interrogation technique are employed to envisage sharp SPR reflectance curves by optimizing the thickness of the gold layer and number of graphene layers. Aside this, an excellent electric field enhancement factor is accomplished near the graphene and sensing layer interface, which dramatically escalates the absorption of glucose and gas analytes. Subsequently, several performance measuring factors such as sensitivity, detection accuracy, resonance angle shift, and quality factor are thoroughly scrutinized and compared with other conventional SPR sensors. Moreover, simulation results reveal some noteworthy upshots like sensitivity of 275.15°/RIU, detection accuracy of 1.41/°, and quality factor of 76.2 that are obtained for glucose analytes, whereas sensitivity of 92.1°/RIU, detection accuracy of 2.55/° and quality factor of 230.2 are attained for gaseous analytes. Interestingly, it is found that the aforementioned parameters fitted excellently with a linear trend line, which leads to accurate investigation of glucose concentration as well as gaseous analytes. Hence the suggested structure opens up an avenue for suitable biomedical application.

Detailed optical analysis of 100 MeV Ni7+ ion irradiated WO3 thin films using Surface Plasmon Resonance

Modifications in the structural, optical properties and surface morphology of RF sputtered WO3 thin films after irradiation with 100 MeV Ni7+ ions have been reported in the present article. The WO3 thin films were deposited at different sputtering pressures (10–50 mTorr). Despite the grain growth due to irradiation, no structural phase transformation has been observed for the WO3 thin films deposited up to 30 mTorr growth pressure. However, complete amorphization post irradiation was detected for the orthorhombic WO3 thin film grown at 50 mTorr sputtering pressure. AFM images indicated that the pristine WO3 thin film consists of uniform grains having smooth surface morphology. Upon irradiation, grain size increased consistently along with increase in surface roughness (Rq) at all sputtering pressures. The root mean square roughness (Rq) estimated from AFM analysis increased from 1.76 nm in pristine film to 9.89 nm in response to irradiation at a fluence of 1 × 1012 ions cm−2. A systematic decrease in optical band gap has been observed with irradiation, which can be correlated with Ni7+ ion induced mid-gap and near band edge defect states. Surface Plasmon Resonance (SPR) technique has been recognized as an appropriate tool to study the optical properties of pristine and irradiated WO3 thin films. SPR reflectance curves were recorded in angular interrogation mode at 633 nm excitation wavelength for pristine and Ni7+ ions irradiated WO3 films deposited at varying deposition pressure.

Table top surface plasmon resonance measurement system for efficient urea biosensing using ZnO thin film matrix.

The present report addresses the application of surface plasmon resonance (SPR) phenomenon for urea sensing. The former promises a high sensitivity, label-free detection, and real-time information by monitoring the refractive index change at the metal–dielectric interface. In the present report, a highly sensitive urea biosensor has been developed by integrating a ZnO thin film matrix with the SPR technique. Kretschmann configuration has been used to excite the surface plasmon (SP) modes at the ZnO–metal (gold) interface using an indigeneously developed table top SPR measurement setup. Urease (Urs), the urea-specific enzyme, has been immobilized on the surface of ZnO thin film by physical adsorption technique. The SPR reflectance curves were recorded for the prism/Au/ZnO/Urs system in angular interrogation mode with phosphate-buffered saline (PBS) solution as the liquid media. The SPR resonance angle is found to be shifted toward a lower angle from 49.1 to 42.0 deg with an increase in the urea concentration (0 to 300 mg/dl) in the PBS solution. The developed sensor (prism/Au/ZnO/Urs) is found to be highly sensitive [sensitivity=0.039 deg/(mg/dl) or 203 deg/RIU] with detection accuracy of 0.045(deg)(−1).

Sensitive optical biosensor based on surface plasmon resonance using ZnO/Au bilayered structure

The present article represents the preparation of highly sensitive optical biosensor using an indigenously assembled table top Surface plasmon resonance (SPR) technique. Surface plasmon modes have been excited at the ZnO-gold interface exploiting Kretschmann configuration. RF-magnetron sputtering has been utilised to deposit ZnO thin films further used for the immobilization of specific enzyme GOx by physical adsorption technique. The SPR reflectance curves were recorded for the GOx/ZnO/Au/prism system in angular interrogation mode in Phosphate buffer saline (PBS) solution by varying analyte (glucose) concentration from 0mg/dl to 300mg/dl. The transient variation in the intensity of reflectance (i.e. response) at fixed SPR resonance angle for increasing concentration of glucose is also reported. The prepared sensor exhibits enhanced response (0.75 for 25mg/dl) with high specificity and good linearity beyond the physiological range indicating the realization of an efficient optical biosensor.

Surface plasmon resonance study on the optical sensing properties of tin oxide (SnO2) films to NH3 gas

Surface plasmon resonance (SPR) technique is an easy and reliable method for detecting very low concentration of toxic gases at room temperature using a gas sensitive thin film layer. In the present work, a room temperature operated NH3 gas sensor has been developed using a laboratory assembled SPR measurement setup utilising a p-polarized He-Ne laser and prism coupling technique. A semiconducting gas sensitive tin oxide (SnO2) layer has been deposited under varying growth conditions (i.e., by varying deposition pressure) over the gold coated prism (BK-7) to excite the surface plasmon modes in Kretschmann configuration. The SPR reflectance curves for prism/Au/SnO2/air system for SnO2 thin films prepared at different sputtering pressure were measured, and the SnO2 film deposited at 10 mT pressure is found to exhibit a sharp SPR reflectance curve with minimum reflectance (0.32) at the resonance angle of 44.7° which is further used for sensing NH3 gas of different concentration at room temperature. The SPR reflectance curve shows a significant shift in resonance angle from 45.05° to 58.55° on interacting with NH3. The prepared sensor is found to give high sensing response (0.11) with high selectivity towards very low concentration of NH3 (0.5 ppm) and quick response time at room temperature.

Dielectric dispersion of rf Sputter-deposited SnO<sub>2</sub>, ZnO, WO<sub>3</sub> thin films using surface plasmon resonance technique

Surface Plasmon Resonance (SPR) is a highly sensitive technique for investigating the dielectric and optical properties of dielectrics at metal-dielectric interface. In the present article, the dielectric properties of various wide band gap (WBG) semiconductor have been studied using SPR technique at different wavelengths. The metal oxide thin films of interest are tungsten oxide (WO3), tin oxide (SnO2) and zinc oxide (ZnO) which were deposited by rf magnetron sputtering under optimized growth conditions. Gold coated glass prisms have been utlilized to excite the surface plasmon waves at the metal-dielectric (air) interface. When metal oxide thin films are integrated with the surface of metal thin film, a significant shift in the SPR curve has been observed due to change in the propagation constant of Surface Plasmon Wave (SPW) at metal-dielectric interface. The optical and dielectric parameters of WBG thin films were estimated by fitting experimental SPR data with the Fresnel's equations. SPR reflectance curves obtained using laser of various wavelengths were ultilized to determine the wavelength dispersion of the dielectric properties of these metal oxide thin films.

Detection of Neisseria meningitidis using surface plasmon resonance based DNA biosensor

Herein, we report the development of a surface plasmon resonance (SPR) based biosensor for the detection of Neisseria meningitidis DNA employing Kretschmann configuration. Highly c-axis oriented ZnO thin film of thickness 200nm was deposited on gold coated glass prisms by RF sputtering technique. Single stranded probe DNA was immobilized on the surface of ZnO thin film by physical adsorption method. SPR reflectance curves were recorded as a function of incident angle of He–Ne laser beam using a laboratory assembled SPR setup. The prepared biosensor exhibits a linear response towards target meningitidis DNA over the concentration range from 10 to 180ng/μl with a high sensitivity of about 0.03°/(ng/μl) and a low limit of detection of 5ng/μl. The SPR biosensor demonstrated high specificity and long shelf life thus, pointing towards a promising application in the field of meningitidis diagnosis.

Development of Electrochemical and Optical Based Biosensors

During recent years, rapid and highly selective determination of nucleic acid (in particularly, DNA) has gained much importance in the field of disease diagnostics, gene analysis, tissue matching, forensic and environmental protection. Various techniques have been employed for DNA detection like fluorescence, surface plasmon resonance (SPR), quartz crystal microbalance (QCM), piezoelectric, electroluminiscene, and electro-chemical. Among all these techniques, electro chemical and SPR based biosensors for nucleic acid detection have attracted researchers worldwide due to their high sensitivity, low detection limit, fast response time, wide detection range, good reliability, easy handling and portability. DNA based biosensors rely on the immobilization of a single-stranded oligonucleotide probe onto a surface to recognize by hybridization its complementary target sequence. The probes are typically short oligonucleotides that are capable of hybridizing with specific and unique regions of the target nucleotide sequence. Due to formation of double helical structure between complementary strands, a change in current or SPR angle could be easily observed. In the present study, an effort has been made towards the development of ZnO matrix based biosensors for the detection of Meningitidis using electrochemical (Amperometric) and SPR techniques. The surface plasmon modes have been excited at the ZnO-gold interface in the Kretschmann configuration using a right angled BK7 glass prism (np =1.517) with the help of a laboratory assembled system. The shift in SPR reflectance curve for increasing concentration of target DNA ranging from 10 to180 ng/μl were recorded which shows the promising application of SPR technique towards biosensing. The Sensitivity of the ZnO thin film using SPR is found to be about 0.031°/(ng/μl) with the minimum detection limit of 5 ng/μl. Zinc oxide nanostructures possessing flower-like morphology have been synthesized onto platinized silicon substrate by simple and economical hydrothermal method. The electrochemical sensing response behaviour of the DNA bioelectrode (ssth-DNA/ ZNF/Pt/Si) has been studied by both differential pulse voltammetric (DPV) as well as impedimetric techniques. The fabricated DNA biosensor can quantify wide range of the complementary targets sth-DNA in the range 5–240 ng/μl with good linearity (R=0.98), high sensitivity (168.64μAng/μl/cm2) and low detection limit of about 5ng/μl.

Complex dielectric constant of various biomolecules as a function of wavelength using surface plasmon resonance

Present study focuses on determination of complex dielectric constant of biomolecules as function of frequency by means of surface plasmon resonance (SPR) technique without losing their biofunctionality. Surface plasmon modes have been excited in Kretschmann configuration at interface of ZnO-Au thin films. Various biomolecules (glucose oxidase, cholesterol oxidase, urease, and uricase) have been immobilized successfully on surface of ZnO thin film by electrostatic interaction. SPR reflectance curves for all biomolecules were recorded separately at different wavelengths (407–635 nm). Complex dielectric constant was determined by fitting the experimental SPR data with Fresnel's equations. Dielectric constant of all biomolecules shows frequency dispersion and attributed to ionic polarization.

Detection of amyloid-β42 using a waveguide-coupled bimetallic surface plasmon resonance sensor chip in the intensity measurement mode.

The waveguide-coupled bimetallic (WcBiM) surface plasmon resonance (SPR) chip had been utilized in the intensity interrogation detection mode to detect amyloid-β42 (Aβ42), a biomarker of the Alzheimer disease. The SPR reflectance curve of the WcBiM chip has the narrower full-width-at-half-maximum (FWHM) compared with the SPR reflectance curve of the conventional gold (Au) chip, resulting in the steeper gradient. For the enhancement of resolution, the light source was fixed at an angle where the slope of the reflectance curve is the steepest, and the change in the reflectance was monitored. For the detection of Aβ42, the antibody of Aβ42 (anti-Aβ42) was immobilized on the WcBiM SPR chip using the self-assembled monolayer. The SPR responses, the average changes in the reflectance to the Aβ42 at the concentrations of 100 pg/ml, 250 pg/ml, 500 pg/ml, 750 pg/ml, 1,000 pg/ml, and 2,000 pg/ml were 0.0111%, 0.0305%, 0.0867%, 0.1712%, 0.3021%, and 0.5577%, respectively, for the three replicates. From linear regression analysis, the calibration curve indicated that the SPR response had a linear relation with Aβ42 with the concentration in the range of 100 pg/ml to 2,000 pg/ml. A control experiment showed the anti-Aβ42-modified surface of the WcBiM chip had a high specificity to Aβ42. Thus, the enhanced resolution by utilizing the WcBiM SPR chip in the intensity interrogation detection mode aids the diagnosis of the Alzheimer disease by detecting the Aβ42 around the criteria concentration (500 pg/ml) without any labeling.

Magneto-optical properties of BiFeO3 thin films using surface plasmon resonance technique

Indigeneously assembled surface plasmon resonance (SPR) set up has been exploited to study the magnetic field dependent optical properties of BiFeO3 thin films. BiFeO3 thin films have been deposited onto gold (Au) coated glass prism by using pulsed laser deposition technique. The surface plasmon modes in prism/Au/BiFeO3/air structure have been excited in Kretschmann configuration at the interface of Au/BiFeO3 thin films. The SPR reflectance curves obtained for prism/Au/BiFeO3/air structure were utilized to investigate the optical properties of BiFeO3 thin films at optical frequency (λ=633nm) as a function of applied magnetic field. SPR curves shows a continuous shift towards lower angles with increasing applied magnetic field, which indicate the promising application of ferromagnetic BiFeO3 film as a magnetic field sensor. Complex dielectric constant of deposited BiFeO3 film was determined by fitting the experimental SPR data with Fresnel׳s equations. The variation of complex dielectric constant and refractive index of BiFeO3 film was studied with increase in magnetic field, and the sensitivity of magnetic field sensor was found to be about 0.52RIU/T.

Optical properties of WO3 thin films using surface plasmon resonance technique

Indigenously assembled surface plasmon resonance (SPR) technique has been exploited to study the thickness dependent dielectric properties of WO3 thin films. WO3 thin films (80 nm to 200 nm) have been deposited onto gold (Au) coated glass prism by sputtering technique. The structural, optical properties and surface morphology of the deposited WO3 thin films were studied using X-ray diffraction, UV-visible spectrophotometer, Raman spectroscopy, and Scanning electron microscopy (SEM). XRD analysis shows that all the deposited WO3 thin films are exhibiting preferred (020) orientation and Raman data indicates that the films possess single phase monoclinic structure. SEM images reveal the variation in grain size with increase in thickness. The SPR reflectance curves of the WO3/Au/prism structure were utilized to estimate the dielectric properties of WO3 thin films at optical frequency (λ = 633 nm). As the thickness of WO3 thin film increases from 80 nm to 200 nm, the dielectric constant is seen to be decreasing from 5.76 to 3.42, while the dielectric loss reduces from 0.098 to 0.01. The estimated value of refractive index of WO3 film is in agreement to that obtained from UV-visible spectroscopy studies. The strong dispersion in refractive index is observed with wavelength of incident laser light.

Surface plasmon resonance investigation of optical detection in plasma-modified phospholipid layers

We herein report on a study of surface plasmon resonance (SPR) in thin gold (Au) films coated with thin layers of phospholipid material, which had been exposed to an atmospheric pressure (AP) plasma containing both pure Ar and Ar mixed with O2 (Ar/O2, 0.8%). The phospholipid material that we used for the SPR experiments was lecithin, and the AP plasma system was applied in air by means of a radio-frequency (RF) plasma generator. A thin (∼60 nm) film of Au and a thin (∼15 nm) layer of lecithin were deposited and attached to the face of a prism, and surface plasmon modes were excited along the interfaces of the prism-Au-lecithin-air system by means of prism coupling using a He-Ne Laser (632.8 nm). The experimental SPR reflectance curves of the Au-lecithin-air modes were found to be shifted towards those of the Au-air mode with increasing applications of AP RF plasma treatment. From the shifts in the SPR curves, we found that the estimated thickness of the lecithin layer treated with a pure Ar plasma showed a linear decrease with etching rate of about 3 nm per treatment while the thickness of the lecithin layer treated with a mixed Ar/O2 plasma showed a tendency to saturate following a large initial decrease (ca. 14 nm). All these results demonstrate that the use of SPR sensing could facilitate the detection of extremely small variations in plasma-treated films of biomaterials.