Refractive Index Biosensor Research Articles

Sensitivity Enhancement of Group Refractive Index Biosensor through Ring-Down Interferograms of Microring Resonator.

In recent years, silicon-on-insulator substrates have been utilized for high-speed and low-power electronic components. Because of the high refractive index contrast of the silicon wire, its photonic device footprint can be significantly reduced. Moreover, the silicon photonic process is compatible with a complementary metal-oxide-semiconductor fabrication, which will benefit the high-density optoelectronic integrated circuits development. Researchers have recently proposed using the microring resonator (MRR) for label-free biosensing applications. The high-quality factor caused by the substantial electric field enhancement within the ring makes the MRR a good candidate for biomolecule detection under low analyte concentration conditions. This paper proposes an MRR chip to be a biosensor on the silicon platform through the relative displacement between the spatial ring-down interferograms at various cladding layers. The higher-order ring-down of the spatial interference wave packet will enhance the biosensing sensitivity after optimizing the coupling, MRR length, and the optical source bandwidth at the fixed optical waveguide loss. Finally, a typical sensitivity of 642,000 nm per refractive index unit is demonstrated under 0.1 μW minimum optical power detection for an MRR with a 100 μm radius. Higher sensitivity can be executed by a narrow bandwidth and lower silicon wire propagation loss.

Simulating a graphene-based acousto-plasmonic biosensor to eliminate the interference of surrounding medium.

The presence of species other than the target biomolecules in the fluidic analyte used in the refractive index biosensor based on the surface plasmon resonances (SPRs) can lead to measurement ambiguity. Using graphene-based acousto-plasmonic biosensors, we propose two methods to eliminate any possible ambiguity in interpreting the measured results. First, we take advantage of the dynamic tunability of graphene SPRs in the acousto-plasmonic biosensor with a surface acoustic wave (SAW) induced uniform grating, performing measurements at different applied voltages. Second, a single measurement employing a similar biosensor but with SAW-induced dual-segment gratings. The numerical results show the capability of both methods in decoupling the effect of the target analyte from the other species in the fluid, enabling interpreting the measurement results with no ambiguity. We also report the results of our numerical investigation on the effect of measuring parameters like the target layer effective refractive index and thickness, and the fluid effective refractive index, in addition to the controlling parameters of the proposed acousto-plasmonic biosensor, including graphene Fermi energy and electrical signaling on the sensing characteristics. Both types of proposed biosensors show promising features for developing the next generation lab-on-a-chip biosensors with minimal cross-sensitivities to non-target biomolecules.

Surface Plasmon Resonance–Based Refractive Index Biosensor: an External Sensing Approach

A surface plasmon resonance (SPR)-based sensor founded on photonic crystal fiber (PCF) is suggested and numerically analyzed in the manuscript. The refractive index (RI) detecting SPR-based sensor has the ability to identify the analyte range from 1.33 to 1.4. Pure silica is used as a base material and it has high RI value than the analyte RI. Furthermore, an analyte layer and chemically stable gold (Au) layer are also placed at the sensor design. The simulations are done based on the finite element method (FEM). Here, the scaled-down approach has the necessity to increase phase matching point within the core mode and surface plasmon polariton (SPP) mode which tends to the sensor to reach high sensitivity response. At the intersect point of core and SPP mode, the loss curve shows a maximum peak value. The suggested sensor shows the highest wavelength sensitivity (WS) response of 35,943.22 nm/RIU, amplitude sensitivity (AS) response of 2321.36 RIU−1, sensor resolution of 9.04 × 10−6 RIU, and figure of merit (FOM) value of 600. It is noted that all the optical parameters show better performance analysis. Furthermore, an external sensing approach provides more fabrication feasibility which marks the offered sensor more suitable for practical experimentation. Besides, the investigated sensor provides the maximum and rapid sensing performance that will be helpful for microfluidic analyte detection, detection of biomolecules, medical diagnostics, virus detection, security, and bio-imaging.

Mid infrared sensing structure based on a metal–insulator–metal waveguides with a triangular-shaped resonator

We designed a high sensitivity plasmonic sensor based on a metal–insulator–metal bus waveguide coupled with a triangular ring-shaped resonator (TRSR) containing silver nanorods working in the mid-infrared region having multiple modes. We applied the two-dimensional finite element method (FEM) for transmittance, electric and magnetic fields, plasmon modes, and sensing performance investigation. The highest sensitivity for aqueous solutions (1.31≤n≤1.41) is relevant for extended applications to biosensing, while geometrical optimization is still possible for higher sensitivity. The developed structure receives the high sensitivity and figure of merit ranging in 1000∼6000 nm/RIU (refractive index unit) and 11.67∼66.67 1/RIU for modes 1–7, respectively. Moreover, the designed structure can serve as the refractive index biosensors, significantly enhancing the sensitivity by 300% compared to its common one.

FEM analysis of a λ3/125 high sensitivity graphene plasmonic biosensor for low hemoglobin concentration detection.

A highly sensitive plasmonic refractive index biosensor for hemoglobin protein detection in blood is presented in the near-infrared region. The proposed Au split-ring resonator structure with an extra arm is used to increase electric field enhancement intensity in the vicinity of the nanostructure, which excites localized surface plasmon resonances in the metal-dielectric interface and leads to unity absorption. The footprint of the proposed structure is λ3/125 (λ denoting center wavelength). Through the results from the finite element method (FEM), by variation of the spacer material, and inserting a graphene layer between the spacer and the gold nanostructure, maximum sensitivities of 1804.1 nm/RIU and 2448.45 nm/RIU are achieved, respectively.

High contrast and sensitive near-infrared refractive index sensors based on metal-dielectric-metal plasmonic metasurfaces

We report a numerical study of metal-dielectric-metal (MDM) plasmonic metasurface-based refractive index sensors that have high contrast and sensitivity in the near-infrared region. The MDM plasmonic metasurface is formed by stacking up silver (Ag) subwavelength disk array on thin silica (SiO2) spacer-layer and Ag film (acting as a reflector) on a silicon substrate. The MDM plasmonic metasurfaces with various heights, Ag disk diameters and SiO2 spacer-layer thicknesses are designated and numerically investigated using a finite-difference time-domain method. As results have shown, the optical properties of the device are weakly dependent on the height of Ag disks, but strongly dependent on the size of Ag disks and SiO2 spacer-layer thickness. By looking at the field distribution at the resonance, the strong confinement of incident light localized inside the SiO2 spacer-layer, thus extremely low reflection closed to 0%, corresponding to the absorption of up to 100% and high quality-factor (Q-factor) of ∼180 have been achieved. Because of operating in the near-infrared range, the proposed MDM plasmonic metasurface has low Ohmic loss, and then the refractive index biosensor based on that shows the figure-of-merit (FOM) to have the contrast and selectivity higher than that of other established MDM plasmonic biosensors. The sensitivities of 1109 nm/RIU and 1290 nm/RIU according to FOMs of 38.8 and 95.3, which correspond to the vapor and liquid sensors, respectively, have been achieved. Our systematic investigation provides useful guidelines for designing MDM plasmonic metasurface sensing devices.

Refractive index sensor for sensing high refractive index bioliquids at the THz frequency

In this paper, a highly sensitive and low loss refractive index (RI) biosensor for high RI bio-analytes detection, such as for cholesterol, nicotine, and bacillus bacteria, is proposed. A novel, to the best of our knowledge, decagonal structure with porous core photonic crystal fiber (PC-PCF) is introduced. The porous core consists of a rectangular sensing hole. The analytes to be sensed are considered in liquid form and infiltrated into the sensing holes, which makes the sensing process simpler and more straightforward. Cladding of the PC-PCF consists of multilayer circular air holes arranged in a decagonal pattern. For durability and stability of the sensor, TOPAS is used as the fiber material. A perfectly matched layer is used for boundary conditions. The correlation among optical power, material, and structural properties is analyzed by the finite element method. The sensing performance of the designed sensor is observed at THz frequency (1.4–3.8 THz). The results under high RI of the analytes (1.52–1.55) are as follows: maximum sensitivity of 98.31% for x polarization and 98.26% for y polarization, very low confinement loss of 1.5 × 10 − 14 d B / m , narrow effective mode area of 1.92 × 10 − 7 m 2 , minimum effective material loss of 0.000164 c m − 1 , and very low waveguide dispersion of 0.002 ± 0.05 ps/THz/cm. In addition, the effect of variation of structural parameters on sensor performance is also analyzed. The proposed PC-PCF-based biosensor can be very useful for sensing higher RI biochemical analytes.

Self-Referenced Refractive Index Biosensing with Graphene Fano Resonance Modes.

A hybrid structure composed of periodic monolayer graphene nanoribbons and a dielectric multilayer structure was designed to generate a Fano resonance (FR). The strong interaction between the surface plasmon resonance of graphene and the dielectric waveguide mode results in the FR. The finite element method is utilized to investigate the behaviors of the FR, and it matches well with the theoretical calculations using rigorous coupled wave theory. The results demonstrate that the profile of the FR can be passively tuned by the period of the graphene nanoribbons and actively tuned by the Fermi level of the graphene. The decoupled nature of the FR gives it potential applications as a self-calibrated refractive index biosensor, and the sensitivity can reach as high as 4.615 μm/RIU. Thus, this work provides a new idea for an excellent self-referencing refractive index biosensor.

Theoretical Model for a Highly Sensitive Near Infrared Biosensor Based on Bloch Surface Wave with Dirac Semimetal.

In this work, we present a theoretical model of a near-infrared sensitive refractive index biosensor based on the truncate 1D photonic crystal (1D PC) structure with Dirac semimetal. This highly sensitive near-infrared biosensor originates from the sharp reflectance peak caused by the excitation of Bloch surface wave (BSW) at the interface between the Dirac semimetal and 1D PC. The sensitivity of the biosensor model is sensitive to the Fermi energy of Dirac semimetal, the thickness of the truncate layer and the refractive index of the sensing medium. By optimizing the structural parameters, the maximum refractive index sensitivity of the biosensor model can surpass 17.4 × 103/RIU, which achieves a certain competitiveness compared to conventional surface plasmon resonance (SPR) or BSW sensors. Considering that bulk materials are easier to handle than two-dimensional materials in manufacturing facilities, we judge that 3D Dirac semimetal and its related devices will provide a strong competitor and alternative to graphene-based devices.

Sensitive Hemoglobin Concentration Sensor Based on Graphene-Plasmonic Nano-structures.

In this paper, half-cylindrical-shaped rods are arranged in a row in order to form hemoglobin concentration sensors. The proposed structures can effectively detect hemoglobin concentrations in blood samples. Five individual structures based on graphene-plasmonic combinations are proposed and investigated. The proposed structures are made of different layers of Au, Ag, SiO2, and graphene. Different plates and cylindrical-shaped graphene layers are introduced in the structures to improve the functionality (absorption peak value and wavelength) of the absorber (sensor). Adding more Au layers strengthens the confinement of the incident electromagnetic waves and improves the absorption factor. Also, in the proposed structures, for improving the results, the effects of the chemical potential of graphene layers and “G” (graphene layer thicknesses) on the absorption peak and wavelength are considered. The final suggested structure indicates unity absorption peak and thus can be utilized in wide ranges of applications. As a refractive index bio-sensor, the structure is considered for detecting hemoglobin concentrations in blood samples which indicates a reasonable sensitivity factor of 570 nm/RIU.

A high-sensitivity refractive index biosensor based on Si nanorings coupled to plasmonic nanohole arrays for glucose detection in water solution

In this paper, a refractive index biosensor is proposed which employs Si photonic nanorings coupled to ring-shaped plasmonic nanohole arrays (PNA) on a hybrid substrate to facilitate sensing of different glucose concentrations in water solution. The proposed structure can be used as a single-mode refractive index biosensor with a high sensitivity of 1278 nm/RIU, a figure of merit (FoM) of 168.1 RIU−1, and good detection accuracy of 0.13 nm−1. The sensitivity and FoM values of the proposed structure are highest in comparison with many reported structures in recent years, while it uses a simple structural topology. The effects of various structural parameters on the reflection spectrum and sensing performance are comprehensively surveyed using the 3D FDTD method. Using the proposed structure, the strength of the interaction between the applied light and the analyte is effectively enhanced and the propagation loss is relatively reduced. Hence, the designed structure is an appropriate candidate for ultrasensitive biosensing applications.

Highly sensitive and tunable refractive index biosensor based on phase change material

Sensitivity is very important while designing any biosensor. We present a tunable and highly sensitive absorbing metasurface for sensing hemoglobin biomolecules. The metasurface is based on phase change material made using different alloy combinations of Ge2Sb2Te5 (GST). Hemoglobin biomolecules are sensed using the perfect absorbing metasurfaces. Three metasurfaces made up of C-shape split-ring resonator and thin wire are investigated. The biosensor is investigated for different phases of GST material and tuning is observed for amorphous GST (aGST) and crystalline GST (cGST). The results are presented in the form of absorption, electric field, and magnetic field. The absorption results for different angles show that the metasurface is angle sensitive. The results are also observed for different geometrical parameters like GST material thickness and gold metasurface thickness. The proposed perfect absorbing sensitive metasurface based on phase-changing material can be used for sensing hemoglobin in biomedical applications.

Design of novel sensitive terahertz metamaterial absorbers based on graphene-plasmonic nanostructures

In this paper, four different configurations of sensitive metamaterial absorbers based on graphene-plasmonic combinations are designed and proposed. The nanostructures are made of graphene, SiO2, aluminum and gold layers on a silicon substrate. Graphene-ring shaped structures with diagonal strips in vertical and horizontal directions are considered in the structures which greatly affect the absorption characteristics (absorption peak value and wavelength). Aluminum layer is used in the structure to prevent the transmission of light throughout some layers and improve the absorption factor. To promote the functionality of the structures, effects of the structural parameters (R1 and R2) and chemical potentials (Ef1, Ef2, Ef3 and Ef4) on the absorption peak are also studied. The four individual configurations with different layers and strip directions demonstrate distinct and different wavelength ranges; structure-1: 45–60 µm, structure-2: 50–70 µm, structure-3: 70–85 µm, and structure-4: 80–100 µm. Thus, they can be utilized for wide categories of applications. Sensitivities of 1500 nm/RIU, 2250/RIU, 3750 nm/RIU and 4850 nm/RIU are obtained for four types, respectively. The proposed structures can be categorized as refractive index biosensors, which indicate acceptable sensitivities and can be used for detection of different elements like hemoglobin and glucose in blood samples.

Refractive index biosensing using near-UV metal–dielectric–metal nanostructured arrays: fabrication and simulation

This work reports the design, simulation, and fabrication of a metal–dielectric–metal (MDM) nanohole array structure toward a realization of a refractive index biosensor. The MDM nanohole array structure operating near the UV range consists of a subwavelength hole array inscribed through the upper aluminum (Al) layer positioned on a stack of a thin silica ( S i O 2 ) spacer and an Al mirror on a silicon substrate. The quality factor of the resonance at ∼ 390 n m of the present nanostructure is ∼ 1.5 t i m e s higher than the previous result owing to the larger fill factor of Al material on the upper layer. This means at the UV range, the designed nanohole array structure closely resembles the dielectric gratings in the visible range. At resonance, we numerically observed a strong confinement of incident light localized inside the subwavelength apertures and the S i O 2 spacer, and thus high absorption and directive emission of up to 99% and ∼ 8.0 d e g , respectively. The MDM nanohole array structure has been fabricated by using plasma-enhanced chemical vapor deposition combining with the focused ion beam, and its reflection experiments are in good agreement with the finite-difference time-domain simulation results. The proposed MDM nanohole array structure can be applicable for a wide variety of plasmonic sensing, in particular for refractive index biosensors. Because of working in the near-UV range, this refractive index biosensor shows the figure of merit to have a selectivity that is ∼ 4.0 t i m e s higher than that of other established plasmonic MDM biosensors.

Design and comparative analysis of aluminum-MoS2 based plasmonic devices with enhanced sensitivity and Figure of Merit for biosensing applications in the near-infrared region

Aluminum (Al)-Molybdenum Disulfide (MoS2) based plasmonic structures act as excellent biosensors when exploited in the near-infrared region. While Al is economical as well as compatible with the optoelectronic devices, MoS2 is an emerging 2D nanomaterial with the promise of initiating better plasmonic activity. Based on Kretschmann's arrangement, we have explored angular interrogation over four different combinations of heterostructures with Al as the plasmonic metal layer, at a wavelength of 1550 nm. After studying the effect of Al thickness on the conventional configuration, the intermediate layers between the metal layer and the analyte were optimized. Inclusion of graphene along with MoS2 results in better interaction with the sensing medium. The effect of including silicon is also studied for sensitivity enhancement. In addition, a comparative analysis of sensor performances of the proposed devices is presented taking into account the two important parameters i.e. sensitivity as well as the Figure of Merit (FOM). Among the optimized multi-layered MoS2 based configurations, a maximum sensitivity of about 141°/RIU is obtained along with FOM of about 335.13 RIU−1. Finally, the single-stranded DNA sensing on the proposed devices shows that the structures can be used as a highly sensitive refractive index biosensor for bio-medical applications.

The potential of terahertz sensing for cancer diagnosis

The terahertz (THz) region lies between the microwave and infrared regions of the electromagnetic (EM) spectrum such that it is strongly attenuated by water and very sensitive to water content. Here, we numerically present what is to our knowledge the detecting system based on THz reflectance spectral responses data in the diagnosis of in vivo and ex vivo of some cancer's samples such as skin, breast and colon cancer tissue samples. The numerical analysis on the use of semiconductor metamaterial design/device as a complex refractive index (CRI) biosensor have been carried out. We demonstrate the application of terahertz pulse detecting (TPD) in reflection geometry for the study of normal and cancerous biological tissues. THz radiation has very low photon energy and thus it does not pose any ionization hazard for biological tissues. The sensitivity of THz radiation to polar molecules, such as water, makes TPD suitable to study the diseases in human body. By studying the THz pulse shape in the time domain, we have been able to differentiate between diseased and normal tissue for the study of basal cell carcinoma (BCC), breast and colon cancers. These results demonstrate the potential of TPD for the study of skin tissue and its related disorders, both in vivo and ex vivo. Findings of this study demonstrate the potential of TPD to depict breast and colon cancers and both in vivo and ex vivo of skin cancer and encourage further studies to determine the sensitivity and specificity of the technique.

Design of dual polarized tetra core PCF based plasmonic RI sensor for visible-IR spectrum

In this research work, a susceptible refractive index (RI) biosensor has been presented which can operate in visible to near-infrared region, i.e (500–2000 nm) on a tetra core “photonic crystal fiber (PCF)” based on the “surface plasmon resonance (SPR).” The efficiency of the proposed RI sensor is analyzed in terms of “wavelength sensitivity (WS), amplitude sensitivity (AS), sensor resolution (SR), and linearity of the resonance wavelength.” Using amplitude interrogation method, maximum AS of 7200 RIU−1 is obtained for x−polarization and 4725 RIU−1 for y−polarization, respectively. Similarly WS of 5000 nmRIU−1 and 10000 nmRIU−1 is obtained using a wavelength interrogation method for x−andy−polarization, respectively. Maximum SR of 2.00×10−5RIU and 1.00×10−5RIU is obtained for x−polarization and y−polarization, respectively. The maximum WS, AS, and SR are obtained for the analyte having a RI value of 1.335. A linear relation between resonant wavelength and RI produces R2=0.9832 and 0.9761 for x−andy−polarization, respectively.

Wide-Band/Angle Blazed Dual-Mode Metallic Groove Gratings

A simple approach to acquire wide-band/angle blazing operation in 1-D metallic gratings is investigated by means of mode-matching and equivalent circuit analysis. The gratings are single-groove perfectly conducting gratings that support two propagating guided modes (opposed to typical single-mode cases). It is shown under what conditions one can achieve blazing over a wide range of frequencies and angles. Most importantly, it is identified what governs blazing, in particular the true matching condition that needs to be satisfied, and how the structures' multiple resonances play role in achieving such matching and tailoring the bandwidth. Parameters of the proposed equivalent circuit model for the case of the transverse magnetic (TM) polarization are analytically derived. The accuracy of the models is verified through a comparison against the results of full-wave simulations. The procedure to achieve wide-band/angle blazing performance is delineated, and the design parameters are explicitly given. It is shown that this structure can strongly transfer the power of the TM polarized incident wave to the -1st diffraction order with a fractional bandwidth of ≈50% at working frequency $f_{0}=10$ GHz and for -10 dB specular reflection loss, thus realizing a broadband structure. From the circuit model, an insightful discussion is presented at various mechanisms at play when Bragg and off-Bragg blazing occurs and fully justifies the behavior of the device. The proposed technique opens up new vistas in a wide range of applications, such as spectroscopy, Littrow cavities, beam splitters, refractive index biosensors, and frequency scanned antenna reflectors.

Highly Sensitive Graphene-Based Refractive Index Biosensor Using Gold Metasurface Array

In this letter, a highly sensitive refractive index biosensor applicable in medical devices is proposed. The biosensor design is analyzed for different concentrations of hemoglobin biomolecules. The 70 nm shift in the wavelength is observed for two hemoglobin biomolecules with 1.34 and 1.36 refractive index per unit (RIU). The highest sensitivity of 3500 nm/RIU is observed for these hemoglobin biomolecules. The results are analyzed for absorption, electric field and magnetic field. The design is also analyzed for different geometrical parameters like metasurface array thickness and silicon dioxide (SiO 2 ) layer thickness. The increase in metasurface array thickness reduces the absorption of the design. The increase in the thickness of SiO 2 layer increases the absorption till 0.6 μm thickness than the response remains the same for other thicknesses. The proposed highly sensitive graphene-based metasurface array biosensor is applicable in medical and biosensing photovoltaic devices.

Numerical analysis of effective refractive index bio-sensor based on graphene-embedded slot-based dual-micro-ring resonator

We propose a novel bio-sensor structure composed of slot dual-micro-ring resonators and mono-layer graphene. Based on the electromagnetically induced transparency (EIT)-like phenomenon and the light-absorption characteristics of graphene, we present a theoretical analysis of transmission by using the coupled mode theory and Kubo formula. The results demonstrate the EIT-like spectrum with asymmetric line profile. The mode-field distributions of transmission spectrum are obtained from 3D simulations based on finite-difference time-domain (FDTD) method. Our bio-sensor exhibits theoretical sensitivity of 330 nm/RIU, a minimum detection limit of [Formula: see text] RIU, the maximum extinction ratio of 4.4 dB, the quality factor of [Formula: see text] and a compact structure of [Formula: see text]. Finally, the bio-sensor’s performance is simulated for glucose solution. Our proposed design provides a promising candidate for on-chip integration with other silicon photonic element.