Giant Infrared Sensitivity of Surface Plasmon Resonance-Based Refractive Index Sensor

Surface plasmons (SPs), the coherent charge density oscillations of the electrons bound to the metal-dielectric interface, are dominating the research field of optics. One of the ubiquitous applications of SPs is in sensing. In the present work, we have theoretically studied a couple of surface plasmon resonance (SPR)-based fiber-coupled ultra-sensitive refractive index sensors working in the infrared (IR) region. Either of the copper (Cu) and aluminum (Al) is used as surface plasmon exciting layers in these sensing probes. On the top of the metal layer, field-enhancing graphene and silicon layers are considered. The probes are characterized in terms of sensitivity and detection accuracy (DA). The sensitivities of Cu- and Al-based optimized probes are obtained respectively to be 23.50 and 24 μm/refractive index unit (RIU). To ensure the probes’ compatibility with bio-samples, an extra bio-recognition layer of graphene has been considered over the silicon layer which resulted into the respective sensitivities of 20 and 19.50 μm/RIU for Cu- and Al-based probes with appreciably good DAs.     

Tuning the Fano Resonance Between Localized and Propagating Surface Plasmon Resonances for Refractive Index Sensing Applications

Localized and propagating surface plasmon resonances are known to show very pronounced interactions if they are simultaneously excited in the same nanostructure. Here, we study the Fano interference that occurs between localized surface plasmon resonance (LSPR) and propagating surface plasmon polariton (SPP) modes by means of phase-sensitive spectroscopic ellipsometry. The sample structures consist of periodic gratings of gold nanodisks on top of a continuous gold layer and a thin dielectric spacer, in which the structural dimensions were tuned in such a way that the dipolar LSPR mode and the propagating SPP modes are excited in the same spectral region. We observe pronounced anti-crossing and strongly asymmetric line shapes when both modes move to each other’s vicinity, accompanied of largely increased phase differences between the respective plasmon resonances. Moreover, we show that the anti-crossing can be exploited to increase the refractive index sensitivity of the localized modes dramatically, which result in largely increased values for the figure-of-merit which reaches values between 24 and 58 for the respective plasmon modes.     

Localized Surface Plasmon Resonance-Based Fiber Optic U-Shaped Biosensor for the Detection of Blood Glucose

In the present study, we report the first fiber optic glucose sensor utilizing localized surface plasmon resonance of metal nanoparticles. The fiber was bent in the form of a U-shaped probe for point detection and sensitivity enhancement. The probe was prepared by first attaching gold nanoparticles on the optical fiber core and then immobilizing glucose oxidase over it. The sensor operates in the intensity modulation scheme in which the absorbance is measured with respect to the changes in the glucose concentration. The presence of glucose in the vicinity of the sensing region changes the refractive index of the film due to the chemical reactions with glucose oxidase. The absorbance of the metal nanoparticle changes significantly due to local refractive index change. The fiber optic U-shaped probes of different bending radii were fabricated and it has been found that the probe with bending radius around 0.982?mm possesses the maximum sensitivity. The response of the sensor is fast and requires very small volume of sensing sample (??150???l) which makes it more suitable for commercialization and better than present commercial sensors, which require about 1.5?ml of blood for the detection of glucose.     

Highly Sensitive Refractive Index Sensing with Surface Plasmon Polariton Waveguides

Two prototypical transducer structures are proposed, including a single-waveguide (SW) and Mach–Zehnder interferometer (MZI), implemented with surface plasmon polariton waveguides. Formulas of the output power with structural parameters are deduced respectively. The sensitivities are found to be proportional to S ₁ for SW and S ₂ for MZI, which are dependent on waveguide parameters. Maximizing S ₁ or S ₂ maximizes the corresponding sensitivity, leading to optimized waveguide designs and preferred operating wavelengths. Sensitivity parameters S ₁ and S ₂ are calculated for fundamental modes of V grooves, triangular wedges, and dielectric-loaded surface plasmon polariton waveguides (DLSPPWs), as a function of measured material refractive index n _c (n _c ?=?1.3～1.6, representative refractive index of biochemical matter), at wavelength λ?=?1.55 μm. Finally, the sensitivity S ₂ is analyzed as a function of work wavelength for DLSPPWs with different ridge thickness and specific fluidic SPP waveguide for biochemical sensing is presented. The results offer foundations for application of surface plasmon polariton waveguides in biochemical sensing.     

Cancer Detection with Surface Plasmon Resonance-Based Photonic Crystal Fiber Biosensor

Plasmonics - In this study, early cancer detection of a single living cell is investigated by employing a surface plasmon resonance (SPR)-based photonic crystal fiber (PCF) biosensor structure. The...     

Extra-broad Photonic Crystal Fiber Refractive Index Sensor Based on Surface Plasmon Resonance

Plasmonics - We propose and investigate a photonic crystal fiber (PCF) refractive index sensor with triangular lattice and four large-size channels based on surface plasmon resonance. In such...     

Highly Sensitive Surface Plasmon Resonance Based D-Shaped Photonic Crystal Fiber Refractive Index Sensor

In this article, a D-shaped photonic crystal fiber based surface plasmon resonance sensor is proposed for refractive index sensing. Surface plasmon resonance effect between surface plasmon polariton modes and fiber core modes of the designed D-shaped photonic crystal fiber is used to measure the refractive index of the analyte. By using finite element method, the sensing properties of the proposed sensor are investigated, and a very high average sensitivity of 7700 nm/RIU with the resolution of 1.30 × 10^?5 RIU is obtained for the analyte of different refractive indices varies from 1.43 to 1.46. In the proposed sensor, the analyte and coating of gold are placed on the plane surface of the photonic crystal fiber, hence there is no necessity of the filling of voids, thus it is gentle to apply and easy to use.     

Scaling of Surface Plasmon Resonances in Triangular Silver Nanoplate Sols for Enhanced Refractive Index Sensing

The plasmonic spectra of solution phase ensembles of triangular silver nanoplates have been analysed in order to examine the fundamental properties underlying their size-dependent enhanced refractive index sensitivities. Linewidth studies highlight variations in the response of these solution phase nanostructures to those previously reported for single immobilized triangular nanostructures. The observation of insignificant broadening of the resonance linewidth for larger edge length nanoplates highlights minimal contribution of radiative damping processes at these dimensions. Comparative single nanoplate studies using discrete dipole approximations were performed to analyse the dephasing processes contributing to these reduced linewidths and to determine the key parameters defining the underlying plasmonic response. These single nanoplate approximations highlight the dominance of absorption processes over radiative processes and demonstrate that this dominance can be attributed to the platelet nature/geometry of the nanoplates. These calculations indicate that the higher aspect ratio allows for the maintenance of coherent plasmon oscillations as the edge length of the triangular platelet increases within the sols. Thickness studies verify that this reduction in radiation damping is due to high aspect ratio and can act to confine electromagnetic fields at the nanoplate surface, thereby increasing near-field enhancement and hence the resultant plasmonic refractive index sensitivity.     

Surface Plasmon Resonance-Based Tapered Fiber Optic Sensor: Sensitivity Enhancement by Introducing a Teflon Layer Between Core and Metal Layer

Surface plasmon resonance (SPR)-based tapered fiber optic sensor with Teflon as a dielectric sandwiched between metal and tapered fiber core is proposed. The sensitivity of the sensor has been maximized using different combinations of metal and Teflon layer thicknesses for a given taper ratio. The study shows that the sensitivity of the sensor with the introduction of dielectric (Teflon) increases with the increase in the taper ratio. The maximum sensitivity achieved for a given taper ratio is around 15 times higher than the general SPR-based fiber optic sensor.     

Highly Sensitive Refractive Index Sensor Based on Four-Hole Grapefruit Microstructured Fiber with Surface Plasmon Resonance

Plasmonics - A highly sensitive refractive index (RI) sensor based on four-hole grapefruit fiber with surface plasmon resonance (SPR) has been proposed and theoretically investigated. By coating...     

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.     

Refractive Index Sensor Using Long-Range Surface Plasmon Resonance with Prism Coupler

Plasmonics - Long-range surface plasmon resonance (LRSPR)-based sensors exhibit high sensitivity as compared to the conventional SPR sensors due to low losses. A high refractive index prism and low...     

Graphene-MoS2 Hybrid Structure Enhanced Fiber Optic Surface Plasmon Resonance Sensor

Plasmonics - In this paper, a fiber optic surface plasmon resonance sensor based on graphene-MoS2 hybrid structure is presented. The wavelength interrogation method is employed to analyze the...     

Surface Plasmon Resonance Based Fiber Optic Ammonia Sensor Utilizing Bromocresol Purple

In this paper, a surface plasmon resonance (SPR) based fiber optic ammonia gas sensor has been designed and fabricated using bromocresol purple (BCP) as sensing element. The sensor works under wavelength modulation scheme. The detection of ammonia gas has been carried out at room temperature. Three different kinds of film coating configurations, namely silver + BCP, gold + BCP, and silver + silicon + BCP on the unclad portion of the fiber have been used for studying the role of each layer. Further, to optimize the performance of the sensor, the films of varying thicknesses were coated using thermal evaporation technique. Experiments have been performed for the ammonia concentrations ranging from 0 to 150 ppm around the probe. To record the SPR spectrum, light from a polychromatic source is launched in the fiber and the spectrum is recorded at the other end of the fiber. The spectrum has a peak at lower wavelength while a dip at the higher wavelength. The dip corresponds to SPR while the peak appears to be due to fluorescence properties of the dye. It has been observed that as the ammonia gas comes in contact of the BCP layer, it changes the refractive index of the BCP dye which, in turn, changes the resonance wavelength. Further, the change in refractive index increases as the concentration of ammonia gas increases up to certain concentration of ammonia after that it saturates. Silicon layer has been shown as a protection layer for silver and gold from oxidation and acts as a tuner of wavelength. The proposed ammonia sensor has small response as well as recovery time.     

Refractive Index Sensor Based on Surface Plasmon Resonance Excitation in a D-Shaped Photonic Crystal Fiber Coated by Titanium Nitride

Plasmonics - In this paper, a plasmonic refractive index sensor using a D-shaped photonic crystal fiber coated by titanium nitride has been proposed. The interaction and interplay between fiber...     

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.     

Surface Phonon Resonance Assisted Refractive Index Sensing in Mid-Infrared Wavelength Range

We propose a highly sensitive refractive index sensor based on the surface phonon resonance (SPhR) in the mid-IR spectral range. Surface phonon polaritons (SPhPs) are formed on polar dielectrics such as SiC in mid-IR wavelength range and can be excited with the help of a metallic grating at specific wavelength termed as resonance wavelength. The resonance wavelength of SPhP is significantly affected by the refractive index of the analyte medium placed over the grating. This forms the basis of a refractive index sensor. We have numerically evaluated the performance of such an SPhP-based refractive index sensor by using rigorous coupled wave analysis (RCWA) in terms of sensitivity, detection accuracy, and quality factor. The quality factor and detection accuracy of the sensor formed on SiC substrate are found to be 225.1 RIU^–1 (inverse of refractive index unit) and 6.75, respectively. We have also extended the study for other polar dielectric substrates cBN and GaN and observed considerable enhancement in the performance of the sensor for GaN. The values of quality factor and detection accuracy could be increased to 361.2 RIU^–1 and 10.84, respectively, by using GaN substrate. The proposed sensor finds applications in refractive index sensing of liquids and biomolecules having refractive index in the range 1.33–1.36.

     

Materials Effect in Sensing Performance Based on Surface Plasmon Resonance Using Photonic Crystal Fiber

Plasmonics - This article explores the effect of sensing performances with subject to change in different types of material and this study is carried out by the support of plasmon-coated photonic...     

Influence of Design Parameters on the Performance of a Surface Plasmon Sensor Based Fiber Optic Sensor

In the present work, the influence of two key design parameters, namely, fiber core diameter and sensing region length on the performance of a fiber optic surface plasmon resonance sensor, was experimentally observed. The sensor was designed with a multimode optical fiber of numerical aperture 0.40 and a thin silver layer of 50 nm thickness. The performance evaluation was carried out in terms of three performance parameters: sensitivity, signal-to-noise ratio and resolution. It was found that performance of the sensor tends to improve if fiber of large core diameter is used. Further, sensing region length should be taken as small as possible to attain highly sensitive and accurate sensing procedure. The experimental results are explained in terms of related physical background and mathematical expressions.