Fiber Optic Surface Plasmon Resonance Sensor Research Articles

Rapid detection of Escherichia coli using fiber optic surface plasmon resonance immunosensor based on biofunctionalized Molybdenum disulfide (MoS2) nanosheets

The molybdenum disulfide (MoS2) nanosheets functionalized fiber optic surface plasmon resonance (SPR) immunosensor has been reported for the sensitive detection of Escherichia coli (E. coli). The MoS2 nanosheets were prepared by chemical exfoliation method. The synthesised nanostructures were characterized for their structural, morphological and optical properties. The E. coli monoclonal antibodies were successfully immobilized on the MoS2 functionalized sensing platform via hydrophobic interactions. An alternative method simplifying the antibodies immobilization process by functionalization of 2D nanomaterial (MoS2 nanosheets) for rapid (~15 mins) bacterial quantification is presented in this study. The immunosensor uses wavelength interrogation method and a strong linear relationship (R2 = 0.994) was observed between spectral response of immunosensor and different concentration of E. coli. The nonspecificity and cross-reactivity studies of the developed immunosensor were investigated with detection of Salmonella Typhimurium and Staphylococcus aureus. To demonstrate the practical application, spiked samples of water and orange juice were analysed with acceptable recovery results. The label-free immunosensor exhibits better performance, detection limit (94 CFU/mL), high sensitivity (2.9 nm/1000 CFU mL−1; 3135 nm/RIU) and profound specificity as compared to conventional fiber optic SPR sensor (detection limit: 391 CFU/mL, sensitivity: 0.6 nm/1000 CFU mL−1; 1646 nm/RIU). This sensing platform shows promising applications in regular water and food quality monitoring for various pathogenic microorganisms.

Design and Optimization of Surface Plasmon Resonance Sensor Based on Polymer-Tipped Optical Fiber

In this study, a novel surface plasmon resonance (SPR) sensor based on a single-mode polymer-tipped optical fiber (PTOF) is designed and optimized. The refractive index (RI) measurement is achieved by exciting SPR at the interface between gold film and TiO2 layer coated on the polymer-tip. Finite-difference time-domain (FDTD) method based commercial optiFDTD software is used to optimize the design of the proposed sensor for a better performance related to the materials of the metal film, the shape of polymer-tips, and the thickness of TiO2 layer. The results show that the sensitivity of optimal single-mode PTOF SPR sensor reaches 3798 nm/RIU when analyte RI is 1.333, and reaches 5708 nm/RIU when analyte RI is 1.383. Compared with conventional optical fiber SPR sensors, the single-mode PTOF SPR sensor proposed in the paper is simpler in fabrication, smaller in size, and higher in sensitivity, which has broad application prospect in biomedical sensing.

Fiber optic SPR sensor for human Immunoglobulin G measurement based on the MMF-NCF-MMF structure

Abstract A sensitive, simple fiber optic surface plasmon resonance (SPR) sensor based on the MMF-NCF-MMF structure is proposed in this work. The structure of the sensing part is constructed by a section of noncore fiber (NCF) sandwiched between two multimode fibers (MMF). Gold film with a thickness of 50 nm was uniformly sputtered on the outside surface of the NCF. SPR phenomenon was stimulated and experimentally verified when light propagates at the interface between the dielectric and the gold layers. The length of the NCF section was optimized by experiments and determined to be 12 mm. The refractive index (RI) sensitivity of the SPR sensor is 3475.1 nm/RIU in the RI range of 1.343–1.373. For the realization of human Immunoglobulin G detection, the surface of this SPR sensor needs to be biomodified. A simple process of polyelectrolyte self-assembled multilayers (PSAMs) deposition cycled four times utilizing diallyldimethyl ammonium chloride (PDDA) and styrenesulfonate sodium salt (PSS). And we choose goat anti-human immunoglobulin G-human immunoglobulin G as a bioconjugated pair to examine the bio-sensing effectiveness of this SPR sensor, the maximum sensitivity of Immunoglobulin G (IgG) detection and the limit of detection (LOD) is calculated to be 57.06 nm/(mg/ml) and 1.75 μg/ml, respectively. The proposed sensor is simple, easy to fabricate, low loss, cost-effective and can be used in numerous chemical and biological analyses.

Fiber optic surface plasmon resonance sensor for detection of E. coli O157:H7 based on antimicrobial peptides and AgNPs-rGO

A fiber optic surface plasmon resonance (FOSPR) sensor was developed for detection of Escherichia coli O157:H7 (E. coli O157:H7) in water and juice, based on antimicrobial peptides (AMP), Magainin I, as recognition elements and silver nanoparticles-reduced graphene oxide (AgNPs-rGO) nanocomposites assisted signal amplification. The uniform AgNPs-rGO was fixed on the surface of optical fiber and covered with gold film. Not only was the SPR response greatly enhanced, but also the AgNPs was prevented from being oxidized. The FOSPR showed a sensitivity of about 1.5 times higher than that fabricated only with gold film. In the assay, Magainin I, immobilized on the surface of gold film, could specifically capture E. coli O157:H7, resulting in the wavelength shift of the SPR absorption peak. Under the optimized conditions, the SPR resonance wavelength exhibited a good linear relationship with natural logarithm of the target bacteria concentration in the range of 1.0 × 103 to 5.0 × 107 cfu/mL with the detection limit of 5.0 × 102 cfu/mL (S/N = 3). The FOSPR sensor showed good specificity for E. coli O157:H7 detection compared to other bacteria similar to the target bacterial species. Furthermore, the FOSPR sensor was successfully applied to the detection of E. coli O157:H7 in water, fruit and vegetable juice with the satisfactory recoveries of 88–110%. This assay for E. coli O157:H7 detection possesses high sensitivity, good selectivity, reproducibility and stability. In addition, the AMP based SPR biosensing methodology could be extended to detect a wide variety of foodborne pathogens. Therefore, the versatile method might become a potential alternative tool in food analysis and early clinical diagnosis.

Chalcogenide fiber-optic SPR chemical sensor with MoS2 monolayer, polymer clad, and polythiophene layer in NIR using selective ray launching

Abstract Surface plasmon resonance (SPR) based chalcogenide fiber-optic sensor with polymer clad and MoS2 monolayer is simulated and analyzed in near infrared (NIR) for detection of mixture of alcohols (ethanol and methanol) dissolved in water solution. The proposed fiber optic sensor is analyzed under angular interrogation method, which is based on selective ray (on-axis) launching of monochromatic light into the fiber core at varying angle followed by measuring the loss of power (in dB) after passing through the SPR probe region. The performance of the sensor is analyzed in terms of its figure of merit (FOM). The sensor’s specificity towards alcohols along with considerably larger FOM is achieved by utilizing a polythiophene (PT) layer. The results indicate that longer NIR wavelength (λ) provides superior sensing performance. The sensor’s performance is better for larger volume fraction of methanol in the water solution. The proposed fiber optic SPR sensor has the capability of providing much greater FOM compared with the previously-reported SPR sensors.

Fluoride Fiber-Optic SPR Sensor With Graphene and NaF Layers: Analysis of Accuracy, Sensitivity, and Specificity in Near Infrared

Surface plasmon resonance (SPR) based fluoride fiber-optic sensor with graphene and sodium fluoride layers is simulated and analyzed in near infrared (NIR) for detection of alcohols. Through this paper, the fluoride fiber has been employed for the first time in SPR sensing application. The proposed fiber optic sensor is analyzed under angular interrogation method, which is based on on-axis launching of monochromatic light into the fiber core at varying angle followed by measuring the power transmitted through the SPR probe region. The sensor's specificity towards alcohols plus a significantly increased sensitivity and accuracy are ensured by a polythiophene layer. The results indicate that longer NIR wavelength (λ) provides superior sensing performance. Further, the proposed sensor's performance can be significantly enhanced by tuning the chemical potential (μ) of graphene monolayer. In summary, monochromatic light of λ = 1550 nm and 0.65 eV <; μ <; 0.70 eV provides substantially high performance in terms of sensitivity, accuracy, and figure of merit. The proposed sensor has the capability to provide significantly better performance than previously-reported SPR sensors.

Boronic Acid Functionalized Au Nanoparticles for Selective MicroRNA Signal Amplification in Fiber-Optic Surface Plasmon Resonance Sensing System.

MicroRNA (miRNA) regulates gene expression and plays a fundamental role in multiple biological processes. However, if both single-stranded RNA and DNA can bind with capture DNA on the sensing surface, selectively amplifying the complementary RNA signal is still challenging for researchers. Fiber-optic surface plasmon resonance (SPR) sensors are small, accurate, and convenient tools for monitoring biological interaction. In this paper, we present a high sensitivity microRNA detection technique using phenylboronic acid functionalized Au nanoparticles (PBA-AuNPs) in fiber-optic SPR sensing systems. Due to the inherent difficulty directly detecting the hybridized RNA on the sensing surface, the PBA-AuNPs were used to selectively amplify the signal of target miRNA. The result shows that the method has high selectivity and sensitivity for miRNA, with a detection limit at 2.7 × 10-13 M (0.27 pM). This PBA-AuNPs amplification strategy is universally applicable for RNA detection with various sensing technologies, such as surface-enhanced Raman spectroscopy and electrochemistry, among others.

Graphene enhanced optical fiber SPR sensor for liquid concentration measurement

Abstract A high sensitivity optical fiber Surface Plasmon Resonance (SPR) sensor which based on coreless optical fiber, silver film and graphene, has been designed and implemented for liquid concentration detection. In this paper, Graphene is firstly verified that it can be used to enhance the evanescent field of traditional optical fiber and thus increasing sensitivity in experiment. The sensitivity of proposed sensor is 6.417 nm/%, which is higher than that of the traditional optical fiber SPR sensor according to the comparative experiments. In addition, the proposed sensor is extremely easy to make and the silver film could be protected from oxidation and damage due to the existence of graphene. Moreover, the sensor has pretty small size, immunity to electromagnetic interference, quick response speed and thus can suitable a variety of severe environments and real-time measurement.

Numerical Investigation of a Novel Microscale Swirling Jet Reactor for Medical Sensor Applications

A microscale swirler and corresponding reactor for a recent detection and analysis tool for healthcare applications, Fiber optic-surface plasmon resonance (FO-SPR), is presented in this study. The sensor is a 400 μm diameter needle that works as a detector for certain particles. Currently, the detection process relies on diffusion of particles towards the sensor and hence diagnostic time is rather long. The aim of this study is to decrease that diagnostic time by introducing convective mixing in the reactor by means of a swirling inlet flow. This will increase the particle deposition on the FO-SPR sensor and hence an increase in detection rate, as this rate strongly depends on the aimed particle concentration near the sensor. As the flow rates are rather low and the length scales are small, the flow in such reactors is laminar. In this study, robustly controllable mixing features of a swirling jet flow is used to increase the particle concentration near the sensor. A numerical analysis (CFD) is performed to characterize the flow and a detailed analysis of flow structures depending on the flow rate are reported.

Smart hydrogel-based optical fiber SPR sensor for pH measurements

A hydrogel-coated optical fiber surface plasmon resonance (SPR) sensor based on MMF-SMF-MMF structure has been fabricated for pH measurements. When the solutions with difference pH values contacting the sensing probe, the amount of the dissociated carboxylic ions in the hydrogel will change according to the pH value of the solution. This process will modify the volume and refractive index of the hydrogel, which results in a shift of the SPR wavelength. The experimental sensor is able to indicate pH variations in a wide pH range from 1 to 12, and the maximum pH sensitivity of the proposed sensor can reach 13 nm/pH at higher pH region (8–10 pH). The influence of temperature (in the range of 20 °C–40 °C) on SPR wavelength is found to be weak. Further, the sensor possesses remarkable repeatability and excellent stability. Due to the wide measuring range and simple fabrication process, the sensor is promising to be used for the pH measurements.

Boronic acid functionalized fiber-optic SPR sensors for high sensitivity glycoprotein detection

Boronic acid and its derivatives have shown special capability to cis-diols groups such as glycoprotein and carbohydrate, which has been widely investigated and applied in practical disease diagnosis. Fiber-optic surface plasmon resonance (SPR) sensors with tiny size are very accurate and convenient tools for monitoring the surface interaction in real time. In this paper, phenylboronic acids (PBA) were formed on the sensing surface by coating the fiber surface with a self-assembled monolayer (SAM) with long and short alkyl groups. Compared with commercial available 4-mercaptophenyboronic acid, PBA with long carbon chain provided more flexible space in binding process and achieved much higher sensitivity to glycoprotein. Furthermore, PBA SAM showed much stronger response for Concanavalin A (ConA) than the traditional protein-protein interaction. The limit of detection for ConA was as low as 0.29 nM by L-PBA SAM modified fiber-optic SPR sensors. Finally, we tested different regeneration solutions to remove glycoprotein from the sensor surface and found that only acidic environment was not enough and the protein denaturant such as ethanol or urea was essential for glycoprotein dissociation.

A label-free fiber optic SPR biosensor for specific detection of C-reactive protein

A highly sensitive and label-free fiber optic surface plasmon resonance (SPR) biosensor for specific detection of C-reactive protein (CRP) is proposed and demonstrated. We take dopamine as a cross-linking agent to immobilize the anti-CRP monoclonal antibody, which is an efficient and simple method for specific modification of the fiber optic SPR sensor. The modified sensor can successfully detect CRP specifically. We realize the fabrication of a disposable fiber optic SPR sensor for the CRP specific detection. Through optimizing the immobilization time of anti-CRP monoclonal antibody and the reaction time of antigen and antibody experimentally, the sensor shows a satisfactory linear response (R2 = 0.97) to CRP concentration within the range from 0.01 to 20 μg/ml. Moreover, the highest CRP sensitivity is obtained at 1.17 nm per lg (μg/ml). With the advantages of simple structure and easy fabrication, our sensor is convenient to be batch produced and controlled with good consistency, which is especially suitable for the fabrication of disposable biosensor. It makes sense that our detection can effectively avoid the cross pollution caused by repeated use of the sensor.

Graphene Effect on the Improvement of the Response of Optical Fiber SPR Sensor

In this paper, we present a contribution to the development of a fiber-optic surface plasmon resonance sensor coated with a silver film that is suitable for chemical and biological applications. Indeed, the importance of the choice of the metal deposited on the sensitive zone of the sensor was verified. It has been found that silver-based sensors have better sensitivity. But on the other hand, it suffers from its poor chemical stability. In order to improve sensor stability, a protective layer of graphene was added, and an optimization of the geometrical and physical properties characteristic of the new configuration was presented by using a numerical study. The results obtained show that the sensitivity of the sensor depends on a set of parameters, such as the diameter of the core ( ${D}$ ), the sensitive length ( ${L}$ ), and the thickness of the metal layer ( ${d}$ ) and its nature. The optimal choice of these parameters was fixed for the following values: $D=400~\mu \text{m}$ , $L=15$ mm, and $d=50$ nm.

Fiber-optic surface plasmon resonance sensor based on spectral phase shift interferometric measurements

We demonstrate for the first time a fiber-optic surface plasmon resonance sensor employing the interrogation method based on spectral interferometric measurements of the phase shift between fiber polarization modes. The sensor was fabricated on a specially designed birefringent D-shape fiber made of silica glass, which exhibits modal birefringence of the order of 10−5 and allows for direct deposition of a metal layer in the vicinity of the core. The sensor characteristics measured using the spectral interferometry method were compared with the reference results obtained using the conventional spectral transmission method. The two measuring techniques show similar sensitivity of 2700 nm/RIU for the refractive index of external medium equal to 1.386, however, the detection accuracy of the interferometric method is up to 3 times better.

Long range surface plasmon resonance sensor based on side polished fiber with the buffer layer of magnesium fluoride

In this paper, a theoretical analysis of figure of merit (FOM) of a surface plasmon resonance (SPR) sensor with a buffer layer of magnesium fluoride has been carried out. While the FOM is the ratio of sensitivity and full width at half maximum and it is the measurement index for the SPR performance. The numerical simulation is based on side polished single mode fiber SPR sensor with the 66.5 μm residual fiber thickness and Drude model of metal with the 50 nm gold film thickness. Meanwhile, the comparisons for traditional surface plasmon resonance sensor, symmetrical surface plasmon resonance sensor and long range surface plasmon resonance sensor have performed differently for the FOM. The effect of sensitivity, full width at half maximum and transmittance depth has also been studied. All these studies, lead to a significant analysis to achieve the best possible design of a fiber optic SPR sensor with maximum FOM while the thickness of buffer layer is 100 nm. This design is expected to play an important role on chemical sensing and biological sensing.

Graphene/Au-Enhanced Plastic Clad Silica Fiber Optic Surface Plasmon Resonance Sensor

Owing to its large surface-to-volume ratio and good biocompatibility, graphene has been identified as a highly promising candidate as the sensing layer for fiber optic sensors. In this paper, a graphene/Au-enhanced plastic clad silica (PCS) fiber optic surface plasmon resonance (SPR) sensor is presented. A sheet of graphene is employed as a sensing layer coated around the Au film on the PCS fiber surface. The PCS fiber is chosen to overcome the shortcomings of the structured microfibers and construct a more stable and reliable device. It is demonstrated that the introduction of graphene can enhance the intensity of the confined electric field surrounding the sensing layer, which results in a stronger light-matter interaction and thereby the improved sensitivity. The sensitivity of graphene-based fiber optic SPR sensor exhibits more than two times larger than that of the conventional gold film SPR fiber optic sensor. Furthermore, the dynamic response analyses reveal that the graphene/Au fiber optic SPR sensor exhibits a fast response (5 s response time) and excellent reusability (3.5% fluctuation) to the protein biomolecules. Such a graphene/Au fiber optic SPR sensor with high sensitivity and fast response shows a great promise for the future biochemical application.

A compact, flexible fiber-optic Surface Plasmon Resonance sensor with changeable sensor chips

We propose and demonstrate the concept of a novel compact, flexible fiber optic Surface Plasmon Resonance (SPR) sensor based on a double-pass Kretschmann-type configuration, where the SPR sensor chip can be replaced for various sensing applications. Simulation and experimental results demonstrate that the proposed fiber-optic SPR structure has a sensitivity to salt concentration of around 4.8μW/ppt.

Fibre Optic SPR Sensor Using Functionalized CNTs for the Detection of SMX: Comparison with Enzymatic Approach

A novel approach for the detection of sulfamethaxazole (SMX) based on fibre optic surface plasmon resonance (SPR) technique and functionalized carbon nanotubes (CNTs) is proposed for 0 to 200 μM concentration range. The probe is prepared by immobilizing functionalized CNTs over silver coated unclad core of the fibre. The sensor’s performance is compared with a fibre optic enzyme-based SPR sensor. In the enzyme-based sensor, layer of functionalized CNTs is replaced by the layer of tyrosinase enzyme embedded polyacrylamide gel. It is found that the resonance wavelength in case of enzyme-based probe and the peak absorbance wavelength in the case of CNT-based probe show a red shift as the concentration of SMX is increased. Both the probes are characterized and optimized in terms of sensitivity, limit of detection, selectivity, pH and repeatability. The maximum sensitivities for enzyme and CNT-based sensors are found to be 0.29 and 0.37 nm/μM, respectively. Further, the corresponding limits of detection (LODs) are 1.137 and 0.8918 μM, respectively. The values of LOD are compared with the values reported in the literature for SMX sensors based on other methods/techniques. The proposed sensor utilizing CNTs is found to be the best in terms of LOD. The other advantages of proposed sensor are low cost, high sensitivity and better selectivity in addition to the advantages of remote sensing, real time monitoring, miniaturized probe and ease of handling which are due to the use of optical fibre as substrate for probe fabrication.

Integration of a microfluidic polymerase chain reaction device and surface plasmon resonance fiber sensor into an inline all-in-one platform for pathogenic bacteria detection

We presented the integration of polymerase chain reaction (PCR) microdevice and surface plasmon resonance (SPR) optical fiber sensor into an inline all-in-one device for fluorophore-free detection of PCR amplification. The proposed integrated device consisted of the microfluidic PCR reactor that used channel position-dependent temperature change and the optical fiber SPR sensor with bimetallic (Ag/Al) coating. This all-in-one device performed not only the amplification of DNA of Salmonella spp. (injected volume of 20 microlitter) within 30min, but also the immediately subsequent measurement of the DNA amplicon by the SPR fiber sensor part.Results showed that the SPR sensor signal increased with the cycle number due to the amplicon refractive index smaller than the sum of its constituent dNTP molecules and its minimum resolvable DNA amplicon was that generated at the 15th cycle. The integrated device could serve as a DNA amplification-to-detection instrument. Both the label-free nature that could allow reusability of the presented device and further miniaturization of the whole system can find use in a point-of-care testing with early diagnosis genetic analysis.

Fiber Grating-Assisted Surface Plasmon Resonance for Biochemical and Electrochemical Sensing

Surface plasmon resonance (SPR) optical fiber sensors can be used as a cost-effective and relatively simple-to-implement alternative to well established bulky prism configurations for in situ high sensitivity biochemical and electrochemical measurements. The miniaturized size and remote operation ability offer them a multitude of opportunities for single-point sensing in hard-to-reach spaces, even possibly in vivo . Grating-assisted and polarization control are two key properties of fiber-optic SPR sensors to achieve unprecedented sensitivities and limits of detection. The biosensor configuration presented here utilizes a nanoscale metal-coated tilted fiber Bragg grating (TFBG) imprinted in a commercial single-mode fiber core with no structural modifications. Such sensor provides an additional resonant mechanism of high-density narrow cladding mode spectral combs that overlap with the broader absorption of the surface plasmon for high accuracy interrogation. In this paper, we briefly review the principle, characterization and implementation of plasmonic TFBG sensors, followed by our recent developments of the “surface” and “localized” affinity studies of the biomolecules for real life problems and the electrochemical actives of electroactive biofilms for clean energy resources.