Optical Surface Plasmon Research Articles

Fiber optic coupled surface plasmon resonance sensor based Ag-TiO2 films for hydrogen detection

We propose and demonstrate the fiber optic Surface Plasmon Resonance (SPR) for hydrogen sensing based on Ag/TiO2 at the telecommunications wavelength of 1550 nm . The sensor using TiO2 as a sensitive layer for hydrogen detection consists of a multilayer film of 45 nm Ag/110 nm TiO2 deposited on the coupling prism substrate. An intensity interrogation SPR with Kretschmann configuration is designed, where SPR phenomenon will occur at the interface of the Ag/TiO2 film, and the hydrogen concentration will be detected by measuring the change in the reflected intensity. The sensitivity of the sensor is optimal at an Ag/TiO2 thickness. Simulation and experimental results demonstrate that the fiber-optic SPR sensor developed provides hydrogen sensing and has a high sensitivity to a hydrogen concentration ranging between 14.7% and 25% Hydrogen in Air, reaching 523nW/%.

V groove fiber plasmonic sensor with facile resonance tunability

A compact and ultra-convenient fiber optic surface plasmon resonance sensor is proposed here, deploying a V groove fiber. The open V groove simultaneously acts as a microfluidic channel and core, when it is filled with analytes having high refractive index (RI) whereas plasmons are generated by placing a gold nanowire inside the groove. The characteristics of the sensor have been analyzed using the finite element method and the results demonstrate maximum possible wavelength sensitivity of 20,400 nm/RIU, amplitude sensitivity 700 RIU−1 with corresponding wavelength resolution in the order of 10−6 RIU. Further, the sensor is capable of detecting a wide analyte RI ranging from 1.455 to 1.5 and provides easy tunability of both plasmonic resonance and mode loss without modifying the fiber geometry. So, the proposed sensor could be a potential alternative to the state of art high RI fiber sensors due to its convenient design, easy fabrication procedure, and competitive sensing performance.

Fiber optic surface plasmon resonance based disposable probe for the detection of phosphate ion in soil

Fabrication and characterization of a fiber optic surface plasmon resonance (SPR) based phosphate ion sensor utilizing the coating of cobalt oxide (CoO) over the gold coated unclad core of the fiber have been carried out. The interaction between CoO layer and incoming phosphate ion changes the effective refractive index of the CoO layer which affects the resonance wavelength in the SPR spectrum. The performance of the sensor has been evaluated in acidic solution (pH 4) of inorganic phosphate salt (KH2PO4). The sensor probe has been found to be irreversible implying one time use of the probe or disposable probe. However, the probe works for 0–100 ppm (0–1.03 mM) concentration range of the phosphate ion (H2PO4-). The sensor possesses maximum sensitivity of 0.3155 nm/ppm with 4.96 ppm as the limit of detection. The sensor is highly selective, fast in response and is suitable to determine the phosphate ion concentration in soil. Since the probe has been fabricated on optical fiber it has the advantages of simplicity, miniaturization and low cost.

Graphene oxide biohybrid layer enhances sensitivity and anticorrosive properties in refractive index sensor

Graphene-based materials are capable of enhancing the refractometric response of prism- and optical fiber-based surface plasmon resonance (SPR) sensors; however, complicated multistep and time-consuming attaching processes could limit their practical applications. Herein, for the first time, we demonstrate the immobilization of graphene oxide (GO) submicrometric sheets onto the surface of a gold-coated single-mode fiber using a coating of fungal self-assembling proteins, the hydrophobins (HFBs), as an adhesive nanolayer. Hetero-core fiber tip SPR structures used in this study, consisting of a mirrored multimode–single-mode fiber structure coated with different thin layers (a chromium layer of 3 nm and a gold layer of 30 nm on top) exhibited a refractive index sensitivity (SRI) of 1842 nm RIU−1 (RIU: refractive index unit) at a refractive index (RI) of 1.36. Self-assembly of GO over the SPR fiber tip via HFB, offered an enhancement of up to 20% in the SRI. Moreover, this HFB-GO coating prevented degradation of the Al thin film mirror caused by corrosive salt-water solutions. The process is very simple, harmless, rapid (around 15 min) and scalable, as it is mostly based on one plasma treatment, which can be performed in large chambers and two dip coating steps, in liquid baths. All these features make the use of self-assembled bio/non-bio hybrid coating a green industrial method to improve the performance of SPR fiber biosensors, if compared with traditional chemical methods. Materials applied in this technology, fungal proteins and derivatives of graphite, are sustainable and largely available.

A portable optical fiber biosensor for the detection of zearalenone based on the localized surface plasmon resonance

Abstract With the continuous improvement of people's living standards, food safety issues have gradually become one of the main concerns. Rapid and accurate detection of zearalenone (ZEN) in food has attracted broad research interest. In this work, a low-cost, portable, and reusable optical fiber-based localized surface plasmon resonance (LSPR) biosensor for ZEN was developed. Gold nanoparticles around 25 nm were synthesized and coated on the cross-section of the end of an optical fiber, and then the ZEN nucleic acid aptamer was modified to form the LSPR biosensor for ZEN detection. Results showed that there was a good relationship between ZEN concentrations and the redshifts of LSPR peak in the range of 1 ∼ 480 ng/mL, the limit of detection was 0.102 ng/mL. Moreover, the sensing interface could be easily regenerated by cutting and polishing the end of the optical fiber, indicating that the LSPR biosensor was reusable. It also has exceptional high selectivity for ZEN and good recovery and repeatability, which has a good prospect for the on-site ZEN monitoring.

Fabrication and measurement of fiber optic localized surface plasmon resonance sensor based on gold nanoparticle dimer

Fiber optic localized surface plasmon resonance (FO LSPR) sensors capable of portable, real-time, and remote sensing are emerging with the progress of lab-on-fiber technology. However, the small area of the substrate by the optical fiber often restricts the sensitivity of the FO LSPR sensors. To improve the performance of the FO LSPR sensors, it is necessary to enhance the interactions between incident light and plasmonic nanostructures within a defined region. Dimer in which two nanoparticles are arranged with nanometer spacing can effectively increase the light-nanostructure interactions. It is well known that the nanogap made in the assembled nanoparticles significantly enhances the intensity of the electromagnetic field in the confined area by the hot spot effect. We fabricate the dimers of gold nanoparticles on the optical fiber with benzenethiol using a method that reduces the repulsive force between the nanoparticles. In the dimers, the strong plasmonic interaction between the two nanoparticles produces a longitudinal plasmon coupling band, which is compared to the transverse plasmon band by the monomer-based FO LSPR sensor with a similar density of gold nanoparticles. In the proposed sensor, the longitudinal band displays approximately 9.1 times improved sensitivity. When two types of sensors are applied to the biosensor application, the dimer-based FO LSPR sensor also proves an improved limit of detection of about 2.6 times. This method is expected to become a milestone in the field of measurement for small molecules and low concentration through the advancement of the yield and density of dimers.

A polyaniline/platinum coated fiber optic surface plasmon resonance sensor for picomolar detection of 4-nitrophenol

The paper reports for the first time an innovative polyaniline (PANI)/platinum (Pt)-coated fiber optic-surface plasmon resonance (FO-SPR) sensor used for highly-sensitive 4-nitrophenol (4-NP) pollutant detection. The Pt thin film was coated over an unclad core of an optical fiber (FO) using a DC magnetron sputtering technique, while the 4-NP responsive PANI layer was synthetized using a cost-effective electroless polymerization method. The presence of the electrolessly-grown PANI on the Pt-coated FO was observed by field-emission scanning electron microscopy and subsequently evidenced by energy dispersive X-ray analysis. These FO-SPR sensors with a demonstrated bulk sensitivity of 1515 nm/RIU were then employed for 4-NP sensing, exhibiting an excellent limit-of-detection (LOD) in the low picomolar range (0.34 pM). The proposed sensor’s configuration has many other advantages, such as low-cost production, small size, immunity to electromagnetic interferences, remote sensing capability, and moreover, can be operated as a “stand-alone device”, making it thus well-suited for applications such as “on-site” screening of extremely low-level trace pollutants.

Surface plasmon resonance based fiber optic potassium ion disposable sensing probe for soil testing

Fabrication and characterization of a fiber optic surface plasmon resonance (SPR) based potassium ion (K+) sensor utilizing the coating of dicyclohexeno-18-crown-6 ionophore incorporated in plasticized PVC membrane along with lipophilic pH sensitive dye chromoionophore-I over the silver coated unclad core of the fiber have been carried out. The interaction between ion selective cocktail layer and incoming K+ changes the effective refractive index of the sensing layer which affects the resonance wavelength in the SPR spectrum. To achieve best sensor performance, the thickness of the sensing layer has been optimized. The sensor probe has been found to be irreversible due to the very strong interaction between ionophore and target K+. The ring type structure of ionophore used provides a close fit to the incoming K+ and hence interacts strongly with it which makes K+ incapable of leaving the cavity of the ionophore. The washing of sensor probe with DI water could not break this bonding. This results in one time use of the probe or disposable type sensor probe. However, the probe works for 0 to 180 µg/mL concentration range of K+. The sensor is highly selective to K+ and is not affected by nitrate, phosphate, calcium and sodium ions and can be used to check the concentration of K+ in soil. In addition, the sensor possesses a response time of around 50 sec. Since the probe has been fabricated on optical fiber it has various advantages such as miniaturization, low cost, fast response, capability of real time monitoring and remote sensing.

Optical fiber SPR magnetic field sensor based on photonic crystal fiber with the magnetic fluid as cladding

In this paper, a novel optical fiber surface plasmon resonance (SPR) magnetic field sensor is proposed and experimentally demonstrated. The structure is fabricated by splicing a section of photonic crystal fiber between two multimode fibers. After the structure is coated with 10 nm Cr and 50 nm Au, the high refractive index (RI) sensitivity, from 1973.72 nm RIU−1 to 3223.32 nm RIU−1 in the range of 1.3326–1.3680, verifies the SPR sensor, which is higher than the structure based on single mode fiber with the same coating. In addition, the microscopic mechanism of the tunable characteristics of magnetic fluid RI with the ambient magnetic field is simulated by the molecular dynamics method. To measure the external magnetic field, the sensing region of the SPR sensor is fully inserted in a capillary tube, which is filled with magnetic fluid and sealed with UV glue. A maximum sensitivity of 4.42 nm mT−1 is achieved in the range of 0–24 mT, experimentally. Due to high sensitivity, simple manufacturing and compact size, the proposed sensor possesses attractive application prospects in environmental monitoring, power transmission and biomedical applications.

Tuning the Sensitivity of a Fiber-Optic Plasmonic Sensor: An Interplay Among Gold Thickness, Tapering Ratio and Surface Roughness

The performance of a multimode fiber optic surface plasmon resonance (FO-SPR) sensor has been studied, both theoretically and experimentally, as a function of three crucial parameters - metal layer thickness, tapering ratio (TR) and fiber surface roughness. A combined approach is adopted to investigate the effect of these three parameters on FO-SPR sensor performance instead of considering them individually. Intriguingly, the three parameters are found to be highly correlated and their combined effect significantly influences the FO-SPR sensitivity. It is observed that optimum gold thickness to attain maximal sensitivity varies for different tapering ratios. Moreover, increasing the tapering ratio does not always increase the sensitivity as claimed in previous studies, but instead depends on the fiber surface roughness generated during chemical etching. The optimized FO-SPR sensor exhibits a high sensitivity of 4714 nm RIU <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> with standard glycerol solution in the refractive index (RI) range of 1.372-1.388. Furthermore, the optimized FO-SPR sensor has been employed for label-free detection of bovine serum albumin (BSA) and parathion pesticide. The system is able to detect BSA concentration as low as 1.5 pM and the parathion pesticide is detected at 0.1 ppb levels.

A reflective optical fiber SPR sensor with surface modified hemoglobin for dissolved oxygen detection

A new dissolved oxygen sensor based on optical fiber surface plasmon resonance (SPR) theory and the mechanism of oxygen transporting by hemoglobin was proposed and demonstrated. Gold film was coated on the surface of the optical fiber sensing area, and hemoglobin was modified on the surface of the gold film. The experimental results show that the sensor has good linearity and the limit of detection (LOD) of the sensor is 0.03 mg/L. In addition, in order to enhance the sensitivity of the sensor, the carbon nanotubes were modified on the surface of the gold film of the fiber, and then the hemoglobin was modified in the outermost layer. Through experiments, it was found that the sensitivity of the sensor which modified with carbon nanotubes is 2.8-folds higher than that only modified hemoglobin, the linearity is better, and the LOD is reduced to 0.01 mg/L.

Theoretical investigation of a multi-channel optical fiber surface plasmon resonance hydrogen sensor

We investigate the use and operation of an optical fiber surface plasmon resonance multi-channel hydrogen sensor. The sensor consists of two or more Ag/SiO 2/Pd multilayer structures coated at different locations along the cladding stripped core of an optical fiber. We demonstrate how the sensing response in one channel affects that in others by investigating the effects of the thicknesses of each layer on the sensor sensitivity, detection accuracy and figure of merit. We describe the individual roles of each layer in terms of the sensing and find that the parameter causing the largest degree of crosstalk between the channels is the thickness of the Ag layer which must be very carefully chosen as a result. We find that changes in the SiO 2 and Pd layer thicknesses largely impact the channel in which the change is made so that there is a lot of freedom in choosing these. Finally, we demonstrate measurable operation from three, four, and six-channel sensors and illustrate the fundamental limitations which determine the number of channels which can be used in sensors based on this type of multilayer.

Optical fiber SPR biosensor complying with a 3D composite hyperbolic metamaterial and a graphene film

In the present study, an optical fiber surface plasmon resonance (SPR) biosensor was developed for measuring time- and concentration-dependent DNA hybridization kinetics. Its design complies with a 3D Au / Al 2 O 3 multilayer composite hyperbolic metamaterial (HMM), a graphene film, and a D-shaped plastic optical fiber. According to the numerical simulation and the experimental demonstration, the SPR peak of the designed biosensor can be effectively altered in the range of visible to near-infrared by varying the HMM structure. The sensitivity of the appliance was shown to achieve a value of up to 4461 nm/RIU, allowing its applicability for bulk refractive index sensing. Furthermore, a biosensor designed in this work displayed high-resolution capability (ranging from 10 pM to 100 nM), good linearity, and high repeatability along with a detection limit down to 10 pM, thus suggesting a vast potential for medical diagnostics and clinical applications.

Simply and cost-effectively fabricated AuNP-based fusion spliced transmissive optical fiber LSPR probes.

The transmissive optical fiber localized surface plasmon resonance (LSPR) sensor has become an effective tool in refractive index sensing because of its compact structure, high sensitivity and strong designability. However, its special structure with the sensing region in the middle of the optical fiber leads to the shortcomings of difficult preparation and poor reproducibility, which greatly restricts its application scopes. In order to solve such problem, we design gold nanoparticle (AuNP)-based fusion spliced transmissive optical fiber LSPR probes, which are fabricated via the fusion splicing between the surface modified combination tapered optical fiber and another multimode quartz optical fiber but are totally different from other fabrications of the reported transmissive optical fiber LSPR probes. The fiber probe fabrication is rather simple and cost-effective, only relying on the procedures of combination tapered optical fiber preparation, surface modification and probe fusion splicing, and except for the probe fusion splicing, the other procedures can be mass prepared thus maintaining high efficiency and good reproducibility in fiber probe fabrications. Moreover, according to the experimental verifications, the proposed fiber probes can reach rather high sensitivity in refractive index sensing with high accuracy and good stability in both static and dynamic detecting modes. Therefore, the AuNP-based fusion spliced transmissive optical fiber LSPR probe is a preferred solution for refractive index sensing and can be widely used in various applications.

An Enhanced Plastic Optical Fiber-Based Surface Plasmon Resonance Sensor with a Double-Sided Polished Structure.

An enhanced plastic optical fiber (POF)-based surface plasmon resonance (SPR) sensor is proposed by employing a double-sided polished structure. The sensor is fabricated by polishing two sides of the POF symmetrically along with the fiber axis, and a layer of Au film is deposited on each side of the polished region. The SPR can be excited on both polished surfaces with Au film coating, and the number of light reflections will be increased by using this structure. The simulation and experimental results show that the proposed sensor has an enhanced SPR effect. The visibility and full width at half maximum (FWHM) of spectrum can be improved for the high measured refractive index (RI). A sensitivity of 4284.8 nm/RIU is obtained for the double-sided POF-based SPR sensor when the measured liquid RI is 1.42. The proposed SPR sensor is easy fabrication and low cost, which can provide a larger measurement range and action area to the measured samples, and it has potential application prospects in the oil industry and biochemical sensing fields.

FO-SPR biosensor calibrated with recombinant extracellular vesicles enables specific and sensitive detection directly in complex matrices.

Extracellular vesicles (EVs) have drawn huge attention for diagnosing myriad of diseases, including cancer. However, the EV detection and analyses procedures often lack much desired sample standardization. To address this, we used well‐characterized recombinant EVs (rEVs) for the first time as a biological reference material in developing a fiber optic surface plasmon resonance (FO‐SPR) bioassay. In this context, EV binding on the FO‐SPR probes was achieved only with EV‐specific antibodies (e.g. anti‐CD9 and anti‐CD63) but not with non‐specific anti‐IgG. To increase detection sensitivity, we tested six different combinations of EV‐specific antibodies in a sandwich bioassay. Calibration curves were generated with two most effective combinations (anti‐CD9/Banti‐CD81 and anti‐CD63/Banti‐CD9), resulting in 103 and 104 times higher sensitivity than the EV concentration in human blood plasma from healthy or cancer patients, respectively. Additionally, by using anti‐CD63/Banti‐CD9, we detected rEVs spiked in cell culture medium and HEK293 endogenous EVs in the same matrix without any prior EV purification or enrichment. Lastly, we selectively captured breast cancer cell EVs spiked in blood plasma using anti‐EpCAM antibody on the FO‐SPR surface. The obtained results combined with FO‐SPR real‐time monitoring, fast response time and ease of operation, demonstrate its outstanding potential for EV quantification and analysis.

Gold nanoparticles produced using NaBH4 in absence and in the presence of one-tail or two-tail cationic surfactants: Characteristics and optical responses induced by aminoglycosides

Gold nanoparticles (AuNPs), produced using sodium borohydride in water (AuNPs-H), also in the presence of the surfactants cetyltrimethylammonium bromide (AuNPs-CTAB) and didecyldimethylammonium bromide (AuNPs-D10AB), were characterized and investigated in terms of their optical localized surface plasmon resonance (LSPR) response. The automation of the syntheses improved reproducibility of AuNPs. CTAB was chosen as a model one-tail surfactant capping agent for AuNPs and D10AB (two-tail surfactant) was employed for the first time, as a capping agent for AuNPs. Thus, it was possible to carry out a comparative study for the production of AuNPs, varying the surfactant concentration levels from 1.0 × 10−2 to 1 × 10-4 mol L-1. The LSPR profiles were monitored in function of the time, taking into account storage conditions (at 4 °C and at 27 °C). A more unstable behavior was observed for the AuNPs produced in the presence of D10AB at 1.0 × 10-4 mol L-1, which suggested the disassembling of AuNPs over time. The catalytic activity of the AuNPs was evaluated in the presence of 4-nitrophenol, and the most effective kinetics were observed for systems containing the one-tail surfactant CTAB, at 1.0 × 10−2 mol L-1 (8 min), and for AuNPs-H, which has no organic coating, (6 min). Finally, the evaluation of the optical response from AuNPs was conducted with four aminoglycosides (AMG), indicating that these surfactants prevent interaction between AMG and the surface of the nanoparticles since at higher concentrations of CTAB or D10AB there is no significant variation in the LSPR spectral band in presence of AMG. In contrast, strong interaction, observed as variation of LSPR band, was found for the AuNPs-H-AMG systems.

Plasmonics: A Necessity in the Field of Sensing-A Review (Invited)

ABSTRACT Surface plasmon resonance (SPR) and surface plasmon polariton (SPP) is substantially developing optical sensing approaches that have been working in a wide range of applications, such as biological and chemical analyte detection, bioimaging, food safety, and environmental monitoring to security. Recently, optical fiber-based Surface plasmon resonance (SPR) sensors has gained much attention due to the invention of Photonic crystal fiber (PCF) and microstructured optical fiber (MOF) which offer compact size and light regulatory competencies in unmatched ways. Moreover, the field of sensing has witnessed another type of plasmonic sensors which are based on metal-insulator-metal (MIM) waveguide structure utilizing surface plasmon polariton (SPP) phenomena. This review paper provides an insight into the technological growths in plasmonic sensors based on optical fibers and the MIM platform. We believe that this paper is one of its kind which provides a diverse range of novel plasmonic sensor structures to its readers.

High sensitivity cascaded helical-core fiber SPR sensors

The distributed optical fiber surface plasmon resonance (SPR) sensors have attracted wide attention in biosensing and chemical sensing applications. However, due to the limitation of their sensing structure, it is difficult to adjust their resonant wavelength and sensitivity. Here, novel and flexible cascaded helical-core fiber (HCF) SPR sensors are proposed theoretically and experimentally for distributed sensing applications. It is shown that the resonant wavelength and sensitivity of the sensors can be conveniently controlled by adjusting the twist pitch of the helical core. A high sensitivity of 11,180 nm/RIU for refractive-index measurement ranging from 1.355 to 1.365 is realized experimentally when the twist pitch of the helical core is 1.5 mm. It is worth noting that the sensitivity can be further improved by reducing the twist pitch. For example, the sensitivity of the sensor with a twist pitch of 1.4 mm can theoretically exceed 20,000 nm/RIU. This work opens up a new way to implement multi-parameter or distributed measurement, especially to establish sensing networks integrated in a single-core fiber or a multi-core fiber.

Preparation and characterization of a silver-magnesium fluoride bi-layers based fiber optic surface plasmon resonance sensor

The influence of thickness of silver-magnesium fluoride bi-layers on the sensitivity of SPR based fiber optic sensor has been experimentally examined. The sensitivity is enhanced with increasing magnesium fluoride layer thickness up to 30 nm and decreases at values exceeding 30 nm. The optimum thickness of magnesium fluoride layer was determined to be 30 nm. A sensor fabricated from bi-layers of 40 nm thick silver and 30 nm thick magnesium fluoride demonstrated favorable sensing behavior.