Search Results (23)

The SARS-CoV-2 spike (S1) protein facilitates viral entry through binding to angiotensin-converting enzyme 2 (ACE2), but it also contains an Arg–Gly–Asp (RGD) motif that may enable interactions with RGD-binding integrins on ACE2-negative cells. Here, we provide quantitative evidence for this alternative binding pathway using a live-cell, label-free resonant waveguide grating (RWG) biosensor. RWG technology allowed us to monitor real-time adhesion kinetics of live cells to RGD-displaying substrates, as well as cell adhesion to S1-coated surfaces. To characterize the strength of the integrin–S1 interaction, we determined the dissociation constant using two complementary approaches. First, we performed a live-cell competitive binding assay on RGD-displaying surfaces, where varying concentrations of soluble S1 were added to cell suspensions. Second, we recorded the adhesion kinetics of cells on S1-coated surfaces and fitted the data using a kinetic model based on coupled ordinary differential equations. By comparing the results from both methods, we estimate that approximately 33% of the S1 molecules immobilized on the Nb₂O₅ biosensor surface are capable of initiating integrin-mediated adhesion. These findings support the existence of an alternative integrin-dependent entry route for SARS-CoV-2 and highlight the effectiveness of label-free RWG biosensing for quantitatively probing virus–host interactions under physiologically relevant conditions without the need of the isolation of the interaction partners from the cells. Full article

This investigation presents an overview of various optical biosensors utilized for the detection of cancer cells. It covers a comprehensive range of technologies, including surface plasmon resonance $\left(SPR\right)$ sensors, which exploit changes in refractive index $\left(RI\right)$ at the sensor surface to detect biomolecular interactions. Localized surface plasmon resonance $\left(LSPR\right)$ sensors offer high sensitivity and versatility in detecting cancer biomarkers. Colorimetric sensors, based on color changes induced via specific biochemical reactions, provide a cost-effective and simple approach to cancer detection. Sensors based on fluorescence work using the light emitted from fluorescent molecules detect cancer-specific targets with specificity and high sensitivity. Photonics and waveguide sensors utilize optical waveguides to detect changes in light propagation, offering real-time and label-free detection of cancer biomarkers. Raman spectroscopy-based sensors utilize surface-enhanced Raman scattering $\left(SERS\right)$to provide molecular fingerprint information for cancer diagnosis. Lastly, fiber optic sensors offer flexibility and miniaturization, making them suitable for in vivo and point-of-care applications in cancer detection. This study provides insights into the principles, applications, and advancements of these optical biosensors in cancer diagnostics, highlighting their potential in improving early detection and patient outcomes. Full article

Based on the finite element method, the modulation of the bending wave bandgap and bending waveguide of locally resonant phononic crystal (PnC) plates via a thermal environment is investigated. First, the finite element model of the PnC subjected to a thermal field is introduced; then, the modulation behavior of the bending wave bandgap of the PnC under thermal flux is illustrated; finally, the tunable waveguide of the bending waveguide of the PnC supercell is proposed to be realized by setting up a local heat source. The results show that the injected heat flux causes the PnC unit cell band structure to move toward the low-frequency region while the relative bandgap width increases. The linear defect state of the PnC supercell structure is realized by introducing a local heat source, and a new band is added to the bending wave bandgap of the original supercell. The transmission loss of the bending wave is significantly higher than that of the bending wave bandgap of the supercell in the frequency interval of the linear defect of the supercell, and the frequency response vibrational modes of the supercell structure validate the feasibility of the thermally controlled bending waveguide. This method provides a flexible and efficient control strategy for the frequency tuning of the bending wave bandgap and waveguide. Full article

The study of infected biological cells is crucial in modern biomedical research. This work presents a passive sensing approach using optical resonators, designed to detect malignant diseases within a refractive index (RI) range of 1 to 1.5. A comprehensive theoretical analysis is conducted, yielding an expected limit of detection (LoD) ranging from 0.03 nm/RIU to 0.92 nm/RIU. Furthermore, an in-depth investigation of DNA hybridization is performed, incorporating a 1.8 nm linker layer at the analyte boundary. The refractive indices of single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA) are 1.456 and 1.529, respectively. The novelty of this work lies in the renaturation process of ssDNA to dsDNA, demonstrated through a labeled sensing modality with a measurable shift in the resonance wavelength spectrum. The proposed surface-functionalized resonators, designed using Silicon-on-Insulator (SOI) technology, include (a) a Rectangular Waveguide-based Ring Resonator (RWRiR), (b) a Rectangular Waveguide-based Racetrack Resonator (RWRaR), (c) a Slot Waveguide-based Ring Resonator (SWRiR), and (d) a Slot Waveguide-based Racetrack Resonator (SWRaR). Among these, the SWRiR exhibits the best performance for DNA sensing, achieving a quality factor (Q-factor) of 2216.714, a sensitivity (S) of 54.282 nm/RIU, and a normalized sensitivity (S’) of 0.0349. Full article

This paper explores the potential of phase change materials (PCM) for dynamically tuning the frequency response of a dumbbell u-slot defected ground structure (DGS)-based band stop filter. The DGSs are designed using co-planar waveguide (CPW) line structure on top of a barium strontium titanate (Ba_0.6Sr_0.4TiO₃) (BST) thin film. BST film is used as the high-dielectric material for the planar DGS. Lower insertion loss of less than −2 dB below the lower cutoff frequency, and enhanced band-rejection with notch depth of −39.64 dB at 27.75 GHz is achieved by cascading two-unit cells, compared to −12.26 dB rejection with a single-unit cell using BST thin film only. Further tunability is achieved by using a germanium telluride (GeTe) PCM layer. The electrical properties of PCM can be reversibly altered by transitioning between amorphous and crystalline phases. We demonstrate that incorporating a PCM layer into a DGS device allows for significant tuning of the resonance frequency: a shift in resonance frequency from 30.75 GHz to 33 GHz with a frequency shift of 2.25 GHz is achieved, i.e., 7.32% tuning is shown with a single DGS cell. Furthermore, by cascading two DGS cells with PCM, an even wider tuning range is achievable: a shift in resonance frequency from 27 GHz to 30.25 GHz with a frequency shift of 3.25 GHz is achieved, i.e., 12.04% tuning is shown by cascading two DGS cells. The results are validated through simulations and measurements, showcasing excellent agreement. Full article

Recently, groove gap waveguides (GGWs) have shown significant potential in power handling and bandwidth enhancement compared to conventional waveguides. In this research work, we designed and developed an innovative mushroom-unit-cell-based groove gap waveguide (MGGW) that has shown improved bandwidth compared to conventional GGW structures. The dispersion characteristics of the MGGW were analyzed through the eigenmode solver feature of Microwave Studio CST, which showed that the bandwidth was improved by 8% compared to conventional unit cells in the microwave spectrum. To validate our proposed method for the physical dimensions of unit cell structures, we developed an MGGW structure for the S band, which shows similar trends aligning with the simulation results. The measurement results are promising as a reflection coefficient of less than −20 dB was achieved over the entire band for the WR284 Electronic Industries Alliance (EIA) standard waveguide adapter. The proposed MGGW structure with improved bandwidth will open new doors for researchers to develop ultra-wide bandwidth microwave applications, i.e., filters, transmission lines, resonators, attenuators, etc. Full article

In many noise scenarios, it is necessary to ensure ventilation and noise suppression. In this paper, a ventilated acoustic metamaterial labyrinth plate (VAMLP), formed by an array of labyrinth cells (LCs), is presented. Each labyrinth cell contains four labyrinth waveguide units (WUs). Based on the impedance series principle, an analytical model of the WU was developed and validated by a numerical model and impedance-tube experiments to determine the sound transmission loss of the WU and the LC. The mechanism of the influence of thermo-viscous loss was quantitatively analyzed, and it was clarified that the VAMLP produced sound absorption due to thermo-viscous loss. The change law of impedance at the entrance of the waveguide was analyzed, revealing the noise-reduction mechanism of the labyrinth unit. Combining a BP network and an improved sparrow search algorithm (ISSA), a BP–ISSA optimization model is proposed to optimize the ventilation capacity of the labyrinth cells. The BP-network model can accurately predict the resonance frequency from the structural parameters to form the fitness function. The ISSA optimization model was constructed using the fitness function as the constraint of an equation. Finally, the combination of structural parameters with optimal ventilation capacity was obtained for a given noise frequency. Full article

This paper presents a high-gain, wideband series-fed antenna designed for 5G millimeter-wave (MMW) applications. The structure employs a substrate-integrated-waveguide (SIW)-based power splitter and metamaterials (MMs). The power divider functions effectively at 27.5 GHz, exhibiting an impedance bandwidth from 26.9 to 28.6 GHz. The series-fed dipole is assembled on the SIW-based power splitter, incorporating four dipoles with varying lengths and spacing. The dipoles are connected in series on both sides, running in parallel through a microstrip line. Effectively combining the resonances of the series-fed dipoles and the SIW results in a broad impedance bandwidth, ranging from 26.9 GHz to 34.75 GHz. The design has a gain extending from 9 to 10.5 dBi within the operating bandwidth. To improve gain performance without a substantial increase in antenna size, 11 × 6 MM unit cells were positioned in front of the antenna. As a result, the proposed antenna achieves a maximum gain of 14.1 dBi at 30.5 GHz while maintaining an operational bandwidth of 7.85 GHz. Additionally, due to the arrangement of the two MM-based series-fed dipoles, the antenna exhibits symmetrical dual-beam E-plane radiation at ±20° and 28 GHz in the end-fire direction. The developed system was experimentally validated and an excellent agreement between the simulated and measured data was demonstrated. Full article

A commercially viable metal–dielectric–metal configured triple-band metamaterial absorber is offered in this paper. It is an aggregation of four compact symmetric circles, with a swastika-shaped metal structure, which are bonded by two split-ring resonators (SRRs). Copper (annealed) of electrical conductivity 5.8 × 10⁷ Sm⁻¹ is used for the ground plate and resonator portion of the top layer and an FR 4 dielectric of permittivity 4.3 is used as a substrate. The structural parameters of the unit cell were determined by a trial and error method. FIT-based 3D simulation software (CST microwave studio, 2019 version was used to characterize the proposed perfect metamaterial absorber (PMA). Three resonance peaks were observed at frequencies 3.03, 5.83 and 7.23 GHz with an absorbance of 99.84%, 99.03% and 98.26%, respectively. The numerical result has been validated by some authentic validation methods. Finally, a microwave network analyzer (PNA) of Agilent N5227 with waveguide ports were deployed for measurement. The simulation and experimental results show better harmony. The proposed PMA has a unique design and a small dimension with higher absorption compared to other contemporary studies. This special type of polarization, insensitive S- and C-band PMA, is designed for a telecommunication system via full-time raw satellite and radar feeds. Full article

Optical switching is an essential part of photonic integrated circuits and the focus of research at the moment. In this research, an optical switch design working on the phenomenon of guided-mode resonances in a 3D photonic-crystal-based structure is reported. The optical-switching mechanism is studied in a dielectric slab-waveguide-based structure operating in the near-infrared range in a telecom window of 1.55 µm. The mechanism is investigated via the interference of two signals, i.e., the data signal and the control signal. The data signal is coupled into the optical structure and filtered utilizing guided-mode resonance, whereas the control signal is index-guided in the optical structure. The amplification or de-amplification of the data signal is controlled by tuning the spectral properties of the optical sources and structural parameters of the device. The parameters are optimized first using a single-cell model with periodic boundary conditions and later in a finite 3D-FDTD model of the device. The numerical design is computed in an open-source Finite Difference Time Domain simulation platform. Optical amplification in the range of 13.75% is achieved in the data signal with a decrease in the linewidth up to 0.0079 µm, achieving a quality factor of 114.58. The proposed device presents great potential in the field of photonic integrated circuits, biomedical technology, and programmable photonics. Full article

In this work, a surface plasmon resonance (SPR) biosensor based on a spoon-shaped waveguide combined with an estrogen receptor (ERα) was developed and characterized for the detection and the quantification of estradiol in real water samples. The fabrication process for realizing the SPR platform required a single step consisting of metal deposition on the surface of a polystyrene spoon-shaped waveguide featuring a built-in measuring cell. The biosensor was achieved by functionalizing the bowl sensitive surface with a specific estrogen receptor (ERα) that was able to bind the estradiol. In a first phase, the biosensor tests were performed in a phosphate buffer solution obtaining a limit of detection (LOD) equal to 0.1 pM. Then, in order to evaluate the biosensor’s response in different real matrices related to aquaculture, its performances were examined in seawater and freshwater. The experimental results support the possibility of using the ERα-based biosensor for the screening of estradiol in both matrices. Full article

A novel antenna structure is constructed from cascading multi-stage metamaterial (MTM) unit cells-based printed monopole antenna for 5G mobile communication networks. The proposed antenna is constructed from a printed conductive trace that fetches four MTM unit cells through four T-Resonators (TR) structures. Such a combination is introduced to enhance the antenna gain-bandwidth products at sub-6GHz bands after exiting the antenna with a coplanar waveguide (CPW) feed. The antenna circuitry is fabricated by etching a copper layer that is mounted on Taconic RF-43 substrate. Therefore, the proposed antenna occupies an effective area of 51 × 24 mm². The proposed antenna provides an acceptable matching impedance with S₁₁ ≤ −10 dB at 3.7 GHz, 4.6 GHz, 5.2 GHz, and 5.9 GHz. The antenna radiation patterns are evaluated at the frequency bands of interest with a gain average of 9.1–11.6 dBi. Later, to control the antenna performance, four optical switches based on LDR resistors are applied to control the antenna gain at 5.85 GHz, which is found to vary from 2 dBi to 11.6 dBi after varying the value of the LDR resistance from 700 Ω to 0 Ω, in descending manner. It is found that the proposed antenna provides an acceptable bit error rate (BER) with varying the antenna gain in a very acceptable manner in comparison to the ideal performance. Finally, the proposed antenna is fabricated to be tested experimentally in in free space and in close to the human body for portable applications. Full article

In this paper, a MEMS (Micro Electro Mechanical Systems)-based frequency-tunable metamaterial absorber for millimeter-wave application was demonstrated. To achieve the resonant-frequency tunability of the absorber, the unit cell of the proposed metamaterial was designed to be a symmetric split-ring resonator with a stress-induced MEMS cantilever array having initial out-of-plane deflections, and the cantilevers were electrostatically actuated to generate a capacitance change. The dimensional parameters of the absorber were determined via impedance matching using a full electromagnetic simulation. The designed absorber was fabricated on a glass wafer with surface micromachining processes using a photoresist sacrificial layer and the oxygen-plasma-ashing process to release the cantilevers. The performance of the fabricated absorber was experimentally validated using a waveguide measurement setup. The absorption frequency shifted down according to the applied DC (direct current) bias voltage from 28 GHz in the initial off state to 25.5 GHz in the pull-down state with the applied voltage of 15 V. The measured reflection coefficients at those frequencies were −5.68 dB and −33.60 dB, corresponding to the peak absorptivity rates of 72.9 and 99.9%, respectively. Full article

Lithium niobate (LN) is a promising optical material, its micro–nano structures have been applied to fields such as photonic crystals, nonlinear optics, optical waveguides, and so on. At present, lithium niobate structural colors are rarely studied. Although the nanograting structure was researched, it has such large full width at half-maximum (fwhm) that it cannot achieve red, green, or blue pixels or other high-saturation structural colors, thus, its color printing quality is poor. In this paper, we design and simulate lithium niobate nanodisk metasurface resonators (LNNDMRs), which are based on Mie magnetic dipole (MD) and electric dipole (ED) resonances. In addition, the resonators yield very narrow reflection peaks and high reflection efficiencies with over 80%, especially the reflection peaks of red, green, and blue pixels with fwhm around 11 nm, 9 nm, and 6 nm, respectively. Moreover, output colors of different array cells composed of single nanodisk in finite size are displayed, which provides a theoretical basis for their practical applications. Therefore, LNNDMRs pave the way for high-efficiency, compact photonic display devices based on lithium niobate. Full article

A new waveguide-based surface plasmon resonance (SPR) sensor was proposed and investigated by numerical simulation. The sensor consists of a graphene cover layer, a gold (Au) thin film, and a silicon carbide (SiC) waveguide layer on a silicon dioxide/silicon (SiO₂/Si) substrate. The large bandgap energy of SiC allows the sensor to operate in the visible and near-infrared wavelength ranges, which effectively reduces the light absorption in water to improve the sensitivity. The sensor was characterized by comparing the shift of the resonance wavelength peak with change of the refractive index (RI), which mimics the change of analyte concentration in the sensing medium. The study showed that in the RI range of 1.33~1.36, the sensitivity was improved when the graphene layers were increased. With 10 graphene layers, a sensitivity of 2810 nm/RIU (refractive index unit) was achieved, corresponding to a 39.1% improvement in sensitivity compared to the Au/SiC sensor without graphene. These results demonstrate that the graphene/Au/SiC waveguide SPR sensor has a promising use in portable biosensors for chemical and biological sensing applications, such as detection of water contaminations (RI = 1.33~1.34), hepatitis B virus (HBV), and glucose (RI = 1.34~1.35), and plasma and white blood cells (RI = 1.35~1.36) for human health and disease diagnosis. Full article