Photonic Crystal Fiber-Based Reconfigurable Biosensor Using Phase Change Material

High-performance surface plasmon resonance fiber sensor based on cylindrical vector modes

Cylindrical vector modes with azimuthal polarization and low transmission loss are proposed for the first time to be utilized in a novel design of a surface plasmon resonance (SPR) sensor based on a circular photonic crystal fiber (C-PCF). A C-PCF with a ring of air holes in the cladding is designed where a gold layer with a thickness of 44 nm is coated on the outer cladding surface. The optimal geometric parameters are determined using the finite-element method (FEM) for a high-quality TE₀₁ mode and high sensitivity of the sensor. The proposed SPR sensor shows high sensitivity for analyte refractive index (RI) ranging from n_a = 1.29 to 1.34 over the wavelength range of 1400-2000 nm. It is expected that the proposed sensor can sense low concentrations of hemoglobin, lymphocytes and monocytes of red and white blood cells which are effective in diagnosing the progress of cancer tumors. The maximum sensitivity of 13,800 nm/RIU is obtained in the refractive index environment of 1.33-1.34. The sensor resolution is of the order of 10^-6 and the amplitude sensitivity reaches its maximum of 2380 RIU^-1 at n_a = 1.30 which is the highest value ever reported. Our proposed sensor shows high sensitivity and simultaneously simple design with high performance.

Challenges and perspectives of multi-virus biosensing techniques: A review

In the context of globalization, individuals have an increased chance of being infected by multiple viruses simultaneously, thereby highlighting the importance of developing multiplexed devices. In addition to sufficient sensitivity and rapid response, multi-virus sensing techniques are expected to offer additional advantages including high throughput, one-time sampling for parallel analysis, and full automation with data visualization. In this paper, we review the optical, electrochemical, and mechanical platforms that enable multi-virus biosensing. The working mechanisms of each platform, including the detection principle, transducer configuration, bio-interface design, and detected signals, are reviewed. The advantages and limitations, as well as the challenges in implementing various detection strategies in real-life scenarios, were evaluated. Future perspectives on multiplexed biosensing techniques are critically discussed. Earlier access to multi-virus biosensors will efficiently serve for immediate pandemic control, such as in emerging SARS-CoV-2 and monkeypox cases.

Surface Plasmon Resonance-Based Gold-Coated Hollow-Core Negative Curvature Optical Fiber Sensor

The hollow-core fiber-based sensor has garnered high interest due to its simple structure and low transmission loss. A new hollow-core negative-curvature fiber (HC-NCF) sensor based on the surface plasmon resonance (SPR) technique is proposed in this work. The cladding region is composed of six circular silica tubes and two elliptical silica tubes to reduce fabrication complexity. Chemically stable gold is used as a plasmonic material on the inner wall of the sensor structure to induce the SPR effect. The proposed sensor detects a minor variation in the refractive indices (RIs) of the analyte placed in the hollow core. Numerical investigations are carried out using the finite element method (FEM). Through the optimization of structural parameters, the maximum wavelength sensitivity of 6000 nm/RIU and the highest resolution of 2.5 × 10^-5 RIU are achieved in the RI range of 1.31 to 1.36. In addition, an improved figure of merit (FOM) of 2000 RIU^-1 for Y-polarization and 857.1 RIU^-1 for X-polarization is obtained. Because of its simple structure, high sensitivity, high FOM, and low transmission loss, the proposed sensor can be used as a temperature sensor, a chemical sensor, and a biosensor.

A Multi-Parameter Integrated Sensor Based on Selectively Filled D-Shaped Photonic Crystal Fiber

We propose and numerically investigate a multi-parameter integrated sensor based on a selectively filled D-shaped photonic crystal fiber (PCF). The simple structure can be used to comprehensively detect refractive index, magnetic field, temperature, and voltage. According to the surface plasmon resonance and directional coupling effect, the PCF is coated with a gold nano-film to detect the refractive index of the external environment. In addition, magnetic fluid (water-based Fe₃O₄), toluene, and nematic liquid crystal (NLC E7) are selectively filled into different cladding air holes of the D-shaped PCF to realize the different sensing of the magnetic field, temperature, and voltage. The measurement of refractive index, magnetic field, temperature, and voltage are independent of each other, so these four parameters can be measured simultaneously. The sensing characteristics of the proposed structure are investigated systematically by the finite element method. The results show that the sensitivities of refractive index, magnetic field, temperature, and voltage are 4600 nm/RIU, 1.375 nm/Oe, 15.143 nm/°C, and 0.971 nm/V, respectively. The presented design based on materials selectively filled with D-shaped PCF might enable promising application in multi-parameter optical sensing.

Optical Fiber, Nanomaterial, and THz-Metasurface-Mediated Nano-Biosensors: A Review

The increasing use of nanomaterials and scalable, high-yield nanofabrication process are revolutionizing the development of novel biosensors. Over the past decades, researches on nanotechnology-mediated biosensing have been on the forefront due to their potential application in healthcare, pharmaceutical, cell diagnosis, drug delivery, and water and air quality monitoring. The advancement of nanoscale science relies on a better understanding of theory, manufacturing and fabrication practices, and the application specific methods. The topology and tunable properties of nanoparticles, a part of nanoscale science, can be changed by different manufacturing processes, which separate them from their bulk counterparts. In the recent past, different nanostructures, such as nanosphere, nanorods, nanofiber, core-shell nanoparticles, nanotubes, and thin films, have been exploited to enhance the detectability of labelled or label-free biological molecules with a high accuracy. Furthermore, these engineered-materials-associated transducing devices, e.g., optical waveguides and metasurface-based scattering media, widened the horizon of biosensors over a broad wavelength range from deep-ultraviolet to far-infrared. This review provides a comprehensive overview of the major scientific achievements in nano-biosensors based on optical fiber, nanomaterials and terahertz-domain metasurface-based refractometric, labelled and label-free nano-biosensors.

Enhancement of the SPR Effect in an Optical Fiber Device Utilizing a Thin Ag Layer and a 3092A Liquid Crystal Mixture

This paper is a continuation of previous work and shows the enhancement of the surface plasmon resonance effect in a tapered optical fiber device. The study investigated liquid crystal cells containing a tapered optical fiber covered with a silver nanolayer, surrounded by a low refractive index liquid crystal in terms of the properties of light propagation in the taper structure. Silver films with a thickness of d = 10 nm were deposited on the tapered waist area. Measurements were performed at room temperature; liquid crystal steering voltage U from 0 to 200 V, with and without any amplitude modulation with a frequency of f = 5 Hz, and the wavelength λ ranged from 550 to 1200 nm. A significant influence of the initial arrangement of liquid crystals molecules on light propagation was observed. Three types of liquid crystal cells—orthogonal, parallel, and twist—were considered. During the measurements, resonant peaks were obtained—the position of which can also be controlled by the type of liquid crystal cells and the steering voltage. Based on the obtained results, the best parameters, such as highest peak’s width reduction, and the highest SNR value were received for twisted cells. In addition, the present work was compared with the previous work and showed the possibility of improving properties of the manufactured probes, and consequently, the surface plasmon resonance effect. In the presented paper, the novelty is mainly focused on the used materials as well as suitable changes in applied technological parameters. In contrast to gold, silver is characterized by different optic and dielectric properties, e.g., refractive index, extension coefficient, and permittivity, which results in changes in the light propagation and the SPR wavelengths.

Multi-Analyte Detection Based on Integrated Internal and External Sensing Approach

Highly sensitive, simple and multiplex detection capabilities are key criteria of point-of-care (POC) diagnosis in clinical samples. Here, a simple and highly sensitive multi-analyte detection technique is proposed by using photonic crystal fiber (PCF) based surface plasmon resonance (SPR) sensor that employs both internal and external sensing approaches. The proposed sensor can detect two different analytes simultaneously by the internal and external plasmonic micro-channels. The light propagation through the sensor is controlled by the scaled-down air-holes to excite the free electrons of the plasmonic metal layers. The light-guiding and sensing properties of the sensor is numerically analyzed by using the Finite Element Method (FEM). The proposed sensor shows the maximum wavelength sensitivities (WS) of 12,000 nm/refractive index unit (RIU), and 10,000 nm/RIU, for the internal and external sensing approaches, respectively, and corresponding resolution of 8.33×10-6 RIU and 1.0×10-5 RIU. Moreover, the hybrid sensor is applicable to detect unknown analyte refractive index (RI) in the range of 1.33 to 1.40 which covers extensively investigating analytes such as viruses, different cancer cells, glucose, proteins and DNA/RNA. Due to high sensing performance with multi-analyte detection capability, the proposed sensor can play a significant role to detect bio targets at the POC platform.

Ultra Sensitive Label-Free Detection of Biomolecules Using Vertically Extended Drain Double Gate Si₀.₅Ge₀.₅ Source Tunnel FET

This work reports a vertically extended drain double gate Si_0.5Ge_0.5 source tunnel FET for the biomolecules detection using its electrical properties modulation in presence of biomolecules like cell, DNA, protein, etc. The reported biosensor has a dual source of Si_0.5Ge_0.5 and two cavities above each source-channel interface for the immobilization of biomolecules. This immobilization modulates the screening/tunneling length and energy range available for tunneling due to the dielectric constant and charge density variations of the biomolecules. The dual cavity structure increases the control of biomolecules on the source to channel tunneling probability and thus realizes an increased control on electrical performance parameters of the biosensor enabling it to have a higher sensitivity towards the biomolecules. Further, the cavity length of the reported biosensor is kept as 45 nm making it suitable for large sized biomolecules and polymers detection also. Our study demonstrates that the reported biosensor structure is resilient towards the process variations and temperature effects. Moreover, the effect of dielectric modulation and charge density modulation has also been analyzed in terms of the variation in the drive current, ON state current, threshold voltage, transconductance, and sub-threshold slope (SS). The sensitivity of the reported biosensor is also compared with the existing biosensors and it is found to be highly sensitive.

Design and Performance Analysis of Reconfigurable 1D Photonic Crystal Biosensor employing Ge2Sb2Te5 (GST) for Detection of Women Reproductive Hormones

The present research demonstrates a novel 1D photonic crystal (PhC) based reconfigurable biosensor pertaining to label-free detection of different concentrations of progesterone and estradiol, which play a vital role in developing reproductive hormones in women. The proposed sensor is designed by an alternative arrangement of Na3AlF6 and CeO2, with a central defect layer. A thin layer of novel phase change chalcogenide material (Ge2Sb2Te5) is deposited along the two sides of the defect layer to improve the sensing performance. Numerical simulation of transmission spectrum for TE mode is carried out by using the transfer matrix method (TMM). The mainstay of this research is centered on the assay of shift in the defect mode position and intensity with respect to different concentrations of analyte, by changing the phase of the GST material from amorphous to crystalline. Interestingly, we observed a high tunability in defect mode wavelength, when the phase is changed from amorphous to crystalline, which leads to accomplishment of a high sensitivity of 1.75 nm/nmol/L for progesterone and 20.5 nm/nmol/L for estradiol. Aside from sensitivity, other significant parameters like figure of merit and detection limit are computed, which give a deep insight into the sensing performance. These encouraging sensing performances pave the path for efficient detection of different concentrations of progesterone and estradiol to monitor various gynecological problems in women.