Surface Plasmon Resonance Probe Research Articles

A comparative study of ZnO, AZO, TiO2, Sb2O3, and SnO2 nanomaterials coated SPR based fiber optic refractive index sensors for chemical sensing application

This paper presents a comprehensive investigation of Surface Plasmon Resonance (SPR) based fiber optic sensors tailored for precise detection of refractive index (RI) variations in acetone and ethanol solutions. The sensor probe design incorporates a nanostructure comprising a metal layer (Ag, Al, or Cu) and a metal oxide sensing layer (ZnO, AZO, TiO2, Sb2O3, SnO2) over the fiber core. Employing the Transfer Matrix Method (TMM), optimal layer thicknesses were determined, with a combination of 50 nm Ag and 20 nm metal oxide demonstrating maximum sensitivities. The sensor probes were fabricated using the Radio Frequency (RF) sputtering technique, and their uniformity, elemental composition, and optical properties were assessed through Field Emission Scanning Electron Microscope (FESEM) and ellipsometer analyses.The sensor response of the probes is 12 %, 7.1 %, 10.8 %, 6.08 %, and 11.34 % for acetone and 11.9 %, 9.2 %, 12 %, 7.89 %, and 12.48 % for ethanol. Sensitivities ranged from 2.7 nm/v% to 2.84 nm/v% for acetone and 1.90 nm/v% to 3.02 nm/v% for ethanol, with the SnO2-coated probe exhibiting the highest sensitivity. Further sensitivity enhancement was achieved by introducing a bimetal layer (50 nm Ag/5 nm Sb/20 nm SnO2), resulting in a 15 % increase for ethanol compared to the Ag/SnO2-based SPR probe.

Plasmonic sensor combined with a microcuvette device for monitoring molecule binding processes at ultra-low concentrations

A novel sensing strategy is presented to monitor receptor-target pair interactions at ultra-low concentrations without functionalization processes. The biosensing is made by a sensitive chip and a surface plasmon resonance (SPR) probe connected in series, both built up on multimode plastic optical fibers (POFs). The SPR probe is a conventional D-shaped POF platform, while the capture platform consists of three microholes, containing a few hundred nanoliters each, made in the core of a modified POF. The microholes are filled with a specific receptor solution, which selectively captures the target present in the samples dropped over the filled microholes. Any variation occurring in the microholes due to the molecule binding processes changes the mode profile of the propagated light in the POF's core, modifying the plasmonic effects proportionally to the phenomena under scrutiny. As a proof of concept, the interactions of two receptor-target pairs, estradiol and cortisol to the respective receptors, namely Estrogen Receptor alpha protein (ER) and Glucocorticoid Receptor (GR), were monitored over time in the attomolar range. The receptor-target pair interactions are observed at ultra-low concentrations (order of aM) by monitoring the resonance wavelength shift over time. The proposed sensing approach stands for a novel class of laboratory instrumentation with unprecedented capabilities in terms of compactness, ultra-high sensitivity and low-cost.

Wedged Fiber Optic Surface Plasmon Resonance Sensor for High-Sensitivity Refractive Index and Temperature Measurements

Here, we experimentally demonstrate a wedged fiber optic surface plasmon resonance (SPR) sensor enabling high-sensitivity temperature detection. The sensing probe has a geometry with two asymmetrical bevels, with one inclined surface coated with an optically thin film supporting propagating plasmons and the other coated with a reflecting metal film. The angle of incident light can be readily tuned through modifying the beveled angles of the fiber tip, which has a remarkable impact on the refractive index sensitivity of SPR sensors. As a result, we measure a high refractive index sensitivity as large as 8161 nm/RIU in a wide refractive index range of 1.333-1.404 for the optimized sensor. Furthermore, we carry out a temperature-sensitivity measurement by packaging the SPR probe into a capillary filled with n-butanol. This showed a temperature sensitivity reaching up to -3.35 nm/°C in a wide temperature range of 20 °C-100 °C. These experimental results are well in agreement with those obtained from simulations, thus suggesting that our work may be of significance in designing reflective fiber optic SPR sensing probes with modified geometries.

Mechanically hot-pressed flattened plastic optical fiber-based SPR sensor and its RI sensing

This paper presents a surface plasmon resonance (SPR) sensor based on a flattened plastic optical fiber (POF) for refractive index (RI) sensing. The flattened POF is fabricated by mechanical hot pressing. Afterwards, a thin film of Ag and Au is first deposited on one side of the flat surface to excite the SPR effect. The results show that the flattened POF-based SPR probe coated with the Au film has a sharper SPR peak and a narrower peak width than the probe coated with Ag film. To improve the SPR effect, two flat surfaces of the flattened POF are coated with metal film (Ag and Au). It was found that the sensor showed better RI sensing performance compared to the sensor with only one flat surface coated with metal film. For the flattened POF with two flat surfaces coated with Ag film, achieving the highest RI sensitivity of 2507 nm/RIU in the RI range of 1.33–1.39. The proposed sensor is a low-cost solution for RI measurement with potential applications in the medical and biochemical fields.

Polarization-Multiplexed Incoherent Broadband Surface Plasmon Resonance: A New Analytical Strategy for Plasmonic Sensing.

Surface plasmon resonance (SPR) is an interfacial phenomenon, and the plasmonic sensors are based on the optical excitation of the collective oscillations of free electrons at a metal-dielectric interface. Here, we present the new development of an incoherent broadband (IBB)-SPR probe combining the wavelength interrogation technique with polarization-multiplexing (PM). The performance characteristics of the so-called PMIBB-SPR strategy was validated for the detection of nonenzymatic aqueous urea samples as a representative example for plasmonic sensing with an excellent wavelength and phase sensitivities of 0.1363 nm/mM and 10.34597 mM/deg, respectively. We further explored the missing link between plasmonic polariton resonance (PPR) and polarization modulation via the measurements of the Stokes parameters of the reflected light. This deepens our understanding of the fundamentals of polarization-multiplexed SPR phenomenon at the interface. This study thus paves the way to develop a new-generation analytical technique with the aim of tracking various real-time chemical and biological molecular interactions occurring at the interfaces.

Sensitivity-enhanced fiber-optic surface plasmon resonance sensor utilizing Cu/WS2/PAAG composite film for pH measurement

In this paper, we reported a composite optical fiber probe structure based on a Cu/WS2 coated surface plasmon resonance (SPR) coreless fiber and a microfiber Fiber Bragg Grating (FBG), which can be used for the simultaneous detection of pH and temperature by assembling Polyacrylamide Gel (PAAG) film and Polydimethylsiloxane (PDMS) coating, respectively. The simulation and experimental results show that WS2 nanofilm can effectively enhance the refractive index (RI) sensitivity of 50 nm-Cu film coated optical fiber SPR probe. Due to the swelling ratio of PAAG is regulated by the pH of liquid solution, the sensitivity of pH detection can reach − 4.42 nm/pH in the pH range of 1–9. The temperature response of the pH probe is one of the main factors leading to the pH detection error, and the experimental result is as high as 76.60 pm/°C in the range of 20–60 °C. The temperature sensitivity of the FBG can be increased from 10.4 pm/°C to 85.67 pm/°C by chemical corrosion and covering PDMS coating for temperature compensation.

Plastic Optical Fiber Based SPR Sensor for Simultaneous Measurement of Refractive Index and Liquid Level

In this work, a plastic optical fiber (POF) based surface plasmon resonance (SPR) sensor is proposed and demonstrated for simultaneous measurement of refractive index (RI) and liquid level. The sensor probe is fabricated by polishing the POF and drilling several micro-holes with equal pitch along the fiber axial, after depositing a layer of gold film on the polished region, the SPR probe is obtained. The effects of the micro-hole on the sensing performance are investigated and the structural parameters of the micro hole are optimized. Experimental results show that the changes of the liquid RI can be detected by monitoring the wavelength position of the SPR peak, and the liquid level can be measured by monitoring the deepness of the SPR peak. An RI sensitivity of 2024.41 nm/RIU was obtained in the RI range of 1.335-1.40, and a resolution of 5 mm and measurement range of 25 mm for liquid level measurement were achieved for the probe. The proposed sensor is compact in size and has a very small cross sensitivity for the RI and liquid level measurement, which is useful in the biomedical and industrial sensing fields.

Fiber-optic meta-tip with multi-sensitivity resonance dips for humidity sensing

In response to the requirements of small effective sensing volume for simultaneous interpreting of resonant peaks with different sensing sensitivities, a surface plasmon resonance (SPR) fiber-optic probe based on non-uniform Au groove array is proposed, which realizes relative humidity (RH) sensing by coating silk fibroin film. The RH meta-tip is mainly composed of multi-mode fiber (MMF), a metasurface, and silk fibroin film. The metasurface is transferred to the end face of the MMF by the “contact and separate” transfer method, and then a layer of silk fibroin is coated on the metasurface by dipping method. Because of the interaction of interference and plasma excitation, the proposed SPR probe has many resonance dips with different refractive index (RI) sensitivities, which has the potential to monitor multiple sensing parameters. Because the RI of the silk fibroin film is directly affected by the external environment RH, the phase matching conditions of the propagating surface plasmon polaritons (SPPs) change accordingly, leading to the shifts in the resonance wavelength of those dips. By further improving the functional integration of the fiber-optic SPR probe, the single-ended sensor paves the way for chemical and biological sensing.

Non-productive binding of cellobiohydrolase i investigated by surface plasmon resonance spectroscopy

Future biorefineries are facing the challenge to separate and depolymerize biopolymers into their building blocks for the production of biofuels and basic molecules as chemical stock. Fungi have evolved lignocellulolytic enzymes to perform this task specifically and efficiently, but a detailed understanding of their heterogeneous reactions is a prerequisite for the optimization of large-scale enzymatic biomass degradation. Here, we investigate the binding of cellulolytic enzymes onto biopolymers by surface plasmon resonance (SPR) spectroscopy for the fast and precise characterization of enzyme adsorption processes. Using different sensor architectures, SPR probes modified with regenerated cellulose as well as with lignin films were prepared by spin-coating techniques. The modified SPR probes were analyzed by atomic force microscopy and static contact angle measurements to determine physical and surface molecular properties. SPR spectroscopy was used to study the activity and affinity of Trichoderma reesei cellobiohydrolase I (CBHI) glycoforms on the modified SPR probes. N-glycan removal led to no significant change in activity or cellulose binding, while a slightly higher tendency for non-productive binding to SPR probes modified with different lignin fractions was observed. The results suggest that the main role of the N-glycosylation in CBHI is not to prevent non-productive binding to lignin, but probably to increase its stability against proteolytic degradation. The work also demonstrates the suitability of SPR-based techniques for the characterization of the binding of lignocellulolytic enzymes to biomass-derived polymers.Graphic abstract

Bovine Serum Albumin Protein Detection by a Removable SPR Chip Combined with a Specific MIP Receptor

Nowadays, the development of simple, fast, and low-cost selective sensors to detect substances of interest is of great importance in several application fields. Among this kind of sensors, those based on surface plasmon resonance (SPR) represent a promising category, since they are highly sensitive, versatile, and label-free. In this work, an SPR probe, based on a poly(methyl methacrylate) (PMMA) slab waveguide covered by a gold nanofilm, combined with a specific molecularly imprinted polymer (MIP) receptor for bovine serum albumin (BSA) protein, has been realized and experimentally characterized. The obtained experimental results have shown a limit of detection (LOD) equal to about 8.5 × 10−9 M. This value is smaller than the one achieved by another SPR probe, based on a D-shaped plastic optical fiber (POF), functionalized with the same MIP receptor; more specifically, the obtained LOD was reduced by about three orders of magnitude with respect to the POF configuration. Moreover, concerning the D-shaped POF configuration, no manufacturing process is present in the proposed sensor configuration. In addition, fibers are used only to connect the simple sensor chip with a light source and a detector, promoting a bio-chemical sensing approach based on disposable, low-cost, and removable chips.

High sensitivity and ultra compact fiber-optic microtip SPR thermometer coated with Ag/PDMS bilayer film

In this paper, we report an ultra-compact reflective SPR microtip temperature probe, which can achieve 2-D spatial resolution of several microns. The pencil-shaped all-fiber microtip proposed by us is a SO2 cone-cylinder with a length of 40 μm and a gradient diameter of 2 μm-10 μm, which can be used to develop multi-type tiny functionalized sensors. Due to the strong evanescent field of the ultra-fine microtip, the surface plasmon resonance (SPR) can be effectively stimulated by depositing nano-silver (Ag) film on its surface. Owing to the high refractive index (RI) sensitivity of SPR effect and the high thermo-optic coefficient (TOC) of polydimethylsiloxane (PDMS), the temperature sensitivity of microtip SPR probe coated with PDMS micron-film can reach to 1.985 nm/°C. Teflon 1600 nano-film on the surface of the SPR thermometer can effectively enhance the non-stickiness, moisture-proof and wear resistance. The test results show that the probe is hardly disturbed by humidity. This new sensing platform can be demonstrated by assembling high-performance sensing materials and ultra-compact fiber-optic structures.

Detection of adulteration in pure honey utilizing Ag-graphene oxide coated fiber optic SPR probes.

Fiber optic surface plasmon resonance (SPR) sensor utilizing silver (Ag) and Ag-graphene oxide (GO) is designed and developed for the detection of adulteration of glucose and fructose in pure honey. The concentration range of the two adulterants in pure honey is varied from 4% to 20% with a step change of 4%. The experiments were performed with two different fiber optic probes viz. Probe 1 and Probe 2. Probe 1 is fabricated by coating 50nm Ag film on unclad optical fiber portion and Probe 2 is fabricated by modifying Ag film with GO for sensitivity improvement. The study confirms that using GO modified fiber optic probe, the sensitivity is enhanced to 24% and 37% for glucose and fructose adulterated honey samples respectively. The technique presented in this study is easy, rapid, label free and shows high prospective for the detection of adulterants in pure honey.

Experimental studies on the sensitivity of the propagating and localized surface plasmon resonance-based tapered fiber optic refractive index sensors.

In the present study, the sensitivities of the fiber optic propagating surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR)-based refractive index sensors have been evaluated experimentally for a tapered probe of different taper ratio. The tapering of the fiber probe has been carried out via a heating and stretching technique. The SPR probe has been fabricated by coating a thin film of silver over the core of the tapered optical fiber, while the LSPR probe has been prepared by the coating of the gold nanoparticles over the core of the tapered optical fiber. The increase in the taper ratio increases the sensitivity of both kinds of the probes. The experimentally obtained sensitivity has been compared with the sensitivity of the SPR-based fiber optic refractive index sensors fabricated using various techniques and reported in the literature.

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.

Magnetron Sputtering Coated Optical Fiber Probe Designs for Surface Plasmon Resonance Sensor

In this paper, we have reported the design of the surface plasmon resonance probes prepared from partially etched polymer optical probe and specially tapered single-mode fiber tip probe which are gold coated in magnetron-sputtering unit. The coating parameters and conditions are discussed in details to achieve sensitive surface plasmon resonance probes. The sensor probes work in transmission modes. The gold-coated etched in-line polymer fiber probe demonstrates high sensitivity, ∼2459 nm/RIU and working range includes visible to infrared wavelength. The fiber tip probe with very small interaction area demonstrates sensitivity, ∼166 nm/RIU. The in-line fiber probe could be used for large volume sample and the pointed fiber tip could be used for small volume samples.

Reflectance-based low-cost disposable optical fiber surface plasmon resonance probe with enhanced biochemical sensitivity

A reflectance-based surface plasmon resonance (SPR) fiber sensor with enhanced sensitivity for biochemical sensing is reported after comparing its result with the transmittance-based SPR optical fiber sensors. The fabricated SPR sensor contains a gold-coated multimode fiber with the implementation of a standard source-sensor-spectrometer interrogation system. As the refractive index of the liquid under test is increased, a redshift of the SPR is observed. The coupling of the source to the fiber sensor is optimized by investigating the effect of an intentional misalignment in transmission-based setup. When a fiber tip coated with the silver mirror and the bifurcated fiber bundle is used, an alignment-free disposable sensor probe is achieved. A comprehensive characterization of the proposed reflectance-based SPR probe is discussed. The maximum sensitivity of 3212.19 nm/refractive index unit (RIU) is obtained.

Tuning the field distribution and fabrication of an Al@ZnO core–shell nanostructure for a SPR-based fiber optic phenyl hydrazine sensor

We report the fabrication and characterization of a surface plasmon resonance (SPR)-based fiber optic sensor that uses coatings of silver and aluminum (Al)-zinc oxide (ZnO) core–shell nanostructure (Al@ZnO) for the detection of phenyl hydrazine (Ph-Hyd). To optimize the volume fraction (f) of Al in ZnO and the thickness of the core–shell nanostructure layer (d), the electric field intensity along the normal to the multilayer system is simulated using the two-dimensional multilayer matrix method. The Al@ZnO core–shell nanostructure is prepared using the laser ablation technique. Various probes are fabricated with different values of f and an optimized thickness of core–shell nanostructure for the characterization of the Ph-Hyd sensor. The performance of the Ph-Hyd sensor is evaluated in terms of sensitivity. It is found that the Ag/Al@ZnO nanostructure core–shell-coated SPR probe with f = 0.25 and d = 0.040 μm possesses the maximum sensitivity towards Ph-Hyd. These results are in agreement with the simulated ones obtained using electric field intensity. In addition, the performance of the proposed probe is compared with that of probes coated with (i) Al@ZnO nanocomposite, (ii) Al nanoparticles and (iii) ZnO nanoparticles. It is found that the probe coated with an Al@ZnO core–shell nanostructure shows the largest resonance wavelength shift. The detailed mechanism of the sensing (involving chemical reactions) is presented. The sensor also manifests optimum performance at pH 7.

Electrically Tunable Fiber Optic Sensor Based on Surface Plasmon Resonance

The response of optical fiber surface plasmon resonance (SPR) sensor to potential is monitored in real time. The potential-induced reflectance of a gold-coated optical fiber SPR probe is dependent on potential step width and ionic strength. Wider potential step and stronger ionic strength are generally able to enhance the reflectance and accelerate the response time. The specifically adsorptive anion Cl− provides a pronounced effect on a potential-dependent SPR probe. The exclusive contact of the SPR probe with anion Cl− could significantly slow down the optical response. The work offers opportunities for optical fiber SPR probes to characterize the electrochemical application.

Boronic acid modified fiber optic SPR sensor and its application in saccharide detection

To extend the application of fiber-optic surface plasmon resonance (SPR) sensing technology, the chemical molecular, 2-(((6-aminohexyl)(benzyl)amino)methyl) phenyl boronic acid (ABA-PBA), is prepared as the recognition monolayer and immobilized on the fiber-optic SPR probe. The boronic acid moiety in ABA-PBA monolayer can covalently bond with 1, 2- or 1, 3- diols moiety of sugar. A monolayer of ABA-PBA is assembled on the SPR sensing region and confirmed by surface enhanced Raman scattering (SERS) technique. Spectrophotometric method is used to determine the pKa of ABA-PBA. The interaction between ABA-PBA monolayer and saccharide can induce the shift of resonance wavelength. By using the miniature fiber-optic SPR sensor, saccharide concentration can be monitored in real time. It shows good selectivity to fructose at low concentrations (10–50mM).