Search Results (23)

Biomolecule detection is pivotal in disease diagnosis. In this study, we present a novel aptamer–antibody sandwich module integrated with an imaging weak measurement system to enhance the sensitivity and specificity of biomolecule detection. The feasibility of this approach is demonstrated using CA125. CA125 is a glycoprotein tumor marker widely used for ovarian cancer diagnosis and monitoring, with its level changes closely associated with disease progression. Given its clinical significance, developing highly sensitive and specific CA125 detection methods is crucial for precision medicine. The dual-recognition mechanism combines the high affinity of aptamers and the specificity of antibodies, significantly improving detection performance while utilizing antibodies for signal amplification. In the presence of CA125, the anti-CA125 aptamer immobilized on the chip surface captures the target, which is then specifically bound by the CA125 antibody, forming the aptamer–CA125–antibody complex. This interaction induces a change in the refractive index of the chip surface, which is detected by the imaging weak measurement system and ultimately manifested as a variation in light intensity in the resulting images. The method achieves the highly sensitive detection of CA125 in the 0.01 mU/mL range to 100 U/mL, with preliminary results showing a detection resolution of 3.98 μU/mL and high specificity against non-target proteins. Additionally, detecting CA125 in serum samples further validates the feasibility of the method’s applicability in complex biological matrices. The proposed method offers significant advantages, including high sensitivity, high specificity, label-free, multiplexed detection, low cost, and real-time detection, making it a promising platform for bio-molecule detection with a wide range of applications. Full article

This paper explores the use of superluminal ionization fronts to accelerate and amplify electromagnetic radiation. These fronts are defined as optical boundaries between two regions of a gas, the neutral region and the plasma region, characterized by two different values of the refractive index. For that reason, the front velocity is not necessarily related to the motion of material particles, such as neutral atoms, ions and electrons, which can stay at rest. The fronts can therefore become superluminal without violating causality. In recent years, different experimental configurations, such as the flying focus, showed that it is possible to create superluminal fronts in the laboratory. These fronts can easily be described theoretically in a special reference frame, called the time frame, which is used here. In this frame, superluminal fronts reduce to time refraction, a process that is symmetrical to the well-known optical refraction. It is shown that propagation through such fronts can lead to considerable frequency shifts and energy amplification of probe laser beams. This could eventually be used to develop new sources of tunable radiation. Full article

Rare-earth-doped optical fibres are widely used in lasers and amplifiers. The incorporation of ytterbium and aluminium oxide in a high doping concentration has led to the fabrication of a multi-mode (MM) optical fibre. Within this research, the design, preparation and calculation for the production of a fibre with a targeted 45 μm core diameter are explored. By Energy Dispersive X-ray (EDX) analysis, the doping concentrations of the elements in the core have been measured as 60.4 at.% Al and 1 at.% Yb. Supporting micrographs are used for confirming the core/cladding ratio. Based on the atomic percentage concentration, the calculated refractive index of the multi-element core has an n = 1.61 and an NA = 0.678. Characterisation of the fibre, including absorption and emission cross-section analysis, was performed in order to prove the ability of the fibre to be used for amplification as well as lasing applications. Full article

In this paper, we study the features of the resonant response of a system consisting of two subwavelength one-dimensional periodic structures, considering the dispersion of the refractive index in the presence of optical PT-symmetry for TM polarization. For the considered structure in the green wavelength range, two possible resonance lines were identified at 514.86 nm and 518.5 nm. Ultra-narrow resonances (FWHM of 0.00015 nm) have been obtained for transmitted and reflected waves, and a significant enhancement of the resonant response has been achieved (up to 10⁵ times). The dependence of the system’s optical response on the relative position of its two sub-wavelength gratings and the magnitude of the amplification coefficient of the active part was investigated. This can be used to tune the spectral characteristics of filters, modulate the optical radiation, and create optomechanical sensors such as strain gauges. Full article

Light propagation in multimode fibers is known to experience various nonlinear effects, which are being actively studied. One of the interesting effects is the brightness enhancement at the Raman conversion of the multimode beam in graded index (GRIN) fiber due to beam cleanup at Raman amplification and mode selective feedback in the Raman laser cavity based on fiber Bragg gratings (FBGs) with special transverse structure. It is also possible to explore random distributed feedback based on Rayleigh backscattering on natural refractive index fluctuations in GRIN fibers, but it is rather weak, requiring very high power multimode pumping for random lasing. Here, we report on the first realization of femtosecond pulse-inscribed arrays of weak randomly spaced FBGs in GRIN fibers and study Raman lasing at its direct pumping by highly multimode (M²~34) 940-nm laser diodes. The fabricated 1D–3D FBG arrays are used as a complex output mirror, together with the highly reflective input FBG in 1-km fiber. Above threshold pump power (~100 W), random lasing of the Stokes beam at 976 nm is obtained with output power exceeding 28 W at 174 W pumping. The beam quality parameter varies for different arrays, reaching M²~2 at the linewidth narrowing to 0.1–0.2 nm due to the interference effects, with the best characteristics for the 2D array. Full article

Since the global outbreak of coronavirus disease 2019 (COVID-19), it has spread rapidly around the world. The nucleocapsid (N) protein is one of the most abundant SARS-CoV-2 proteins. Therefore, a sensitive and effective detection method for SARS-CoV-2 N protein is the focus of research. Here, we developed a surface plasmon resonance (SPR) biosensor based on the dual signal-amplification strategy of Au@Ag@Au nanoparticles (NPs) and graphene oxide (GO). Additionally, a sandwich immunoassay was utilized to sensitively and efficiently detect SARS-CoV-2 N protein. On the one hand, Au@Ag@Au NPs have a high refractive index and the capability to electromagnetically couple with the plasma waves propagating on the surface of gold film, which are harnessed for amplifying the SPR response signal. On the other hand, GO, which has the large specific surface area and the abundant oxygen-containing functional groups, could provide unique light absorption bands that can enhance plasmonic coupling to further amplify the SPR response signal. The proposed biosensor could efficiently detect SARS-CoV-2 N protein for 15 min and the detection limit for SARS-CoV-2 N protein was 0.083 ng/mL, with a linear range of 0.1 ng/mL~1000 ng/mL. This novel method can meet the analytical requirements of artificial saliva simulated samples, and the developed biosensor had a good anti-interference capability. Full article

Geophysical techniques were employed to analyze one of the landslides that affected the main access road to Pujilí (Ecuador). A passive seismic technique was utilized to test a total of 70 horizontal to vertical spectral ratio (HVSR) points, complemented by an active seismic-refraction profile and a multichannel analysis of surface waves (MASW) survey. The results from the active geophysical surveys facilitated the determination of the shear-wave-velocity value for the surface materials that were in motion. However, the HVSR provided the fundamental frequency f_o and amplification A_o values of the ground. The Nakamura (1989) relationship was applied to obtain the thickness of the sediments over a compact material from the fundamental frequency of the terrain in a two-layer model. Additionally, constrained models of the shear-wave velocity (V_s) distribution in the landslide area, obtained from the active seismic surveys, were used to invert the ellipticity curves. The results from this inversion were compared with those obtained by applying the Nakamura equation. The landslide-rupture surface was delineated for each type of analysis, which verified the correlation and minimal differences between the results of the three proposed studies, thus validating the procedure. The directivity of the microtremor HVSR signals was also analyzed, demonstrating a relationship with the internal structure of the sliding material. Furthermore, the ability to slide concerning the K_g parameter (vulnerability index, Nakamura, 1989) was studied. The usefulness of the directivity analysis in defining the internal structures in landslide materials and in determining the areas with the most significant instability was demonstrated. Overall, the HVSR is considered valuable when conducting early landslide studies and is helpful in determining the rupture plane while remaining a simple, fast, and economical technique. Full article

In this paper, an analysis of gain properties of a single primitive cell of a one-dimensional photonic crystal with parity–time symmetry is demonstrated for the first time. The proposed simple model makes it possible to study the transmission and amplification properties of the investigated cell made of a wide range of optical materials, taking into account the refractive index of the surrounding medium. This analysis is carried out with the use of a transfer matrix method. The obtained characteristics allow indicating the optimal size of the studied structure providing wave amplification, i.e., a transmittance greater than unity. In this case, the increase in the wave intensity in the gain layer exceeds its decrease in the loss layer. This effect is illustrated with the distributions of the electromagnetic field of waves propagating inside the cell. Full article

A fiber-optic biosensing platform based on ultra-narrowband cladding mode resonances was developed on a high-reflectivity fiber Bragg grating (FBG) for targeting biomolecular detection. The multiple cladding modes with a high sensitivity to the refractive index (RI) were excited in the FBG by coupling between the forward-propagating guided core mode of the multimode fiber and the backward-propagating guided cladding mode of the FBG without any damage to the fiber structure or any change to the standard FBG manufacturing process. The full width at half maximum and the Q-factor of the typical cladding mode resonance operation of the proposed sensor are 80 pm and 19,270, respectively, which are better than those of most fiber-optic biosensors reported to date. In addition, the FBG sensor demonstrated a high sensitivity in protein detection and a high selectivity in serum sample assays. The sensitivity of this sensor was further increased simply by coating it with graphene oxide (GO) sheets on the sensing surface without using a signal amplification strategy. Furthermore, an ultra-low limit of detection (LOD) of 32 pM was obtained by the GO-coated FBG sensor for IgG detection. The proposed FBG sensor provides a competitive fiber-optic platform for biomolecular detection. It has a great potential for applications in label-free biosensing. Full article

Vortex beams carrying orbital angular momentum (OAM) have increasingly attracted attention in the field of optical communication. However, transmission is still an issue due to transmission loss, especially in optical fibers. In this work, we proposed, designed, and fabricated micro spiral phase plates (SPPs) directly on an end facet of a piece of PbSe-doped ring-core fiber (RCF) through two-photon polymerization, realizing the integration of OAM beam generation, transmission, and amplification. The prepared RCF comprises a double-clad structure with a core-clad refractive index difference of 2.2% and the fluorescence range is 1150 nm–1700 nm. The intensity distribution of the OAM beam and the spiral interference fringes were obtained, which indicated that the OAM mode ($\left|l\right|=1, 2, 3, 4$) was generated and transmitted directly within the fiber. The small-signal amplification of four OAM modes was accomplished at 1550 nm under a pump power of 634 mW. The on–off gain is >13.2 dB for all modes and the differential mode gain (DMG) is <1.7 dB. The SPP-carrying RCF structure demonstrates the integration of generation, transmission, and amplification of higher-order OAM modes in all-fiber systems. Full article

In this work, a novel idea of optical switch design based on guided mode resonance in the photonic crystal structure is numerically investigated. The designed switching device work on the principle of optical amplification and wavelength shift of data signal with the help of a control signal. The data signal can be coupled into the waveguide using guided-mode resonance, whereas, a control signal is index-coupled into the waveguide to influence the data signal. The optical switching action is optimized by introducing a photonic crystal cavity and varying the number of photonic crystal elements, where the resonant wavelength, reflection peaks, linewidth, and quality factor of the data signal can be adjusted. The device is based on low refractive index contrast dielectric materials compatible with fiber optic communication and can operate in a near-infrared range of around 1.55 μm. The numerical simulations are carried out in an open source finite-difference time-domain-based software. An optical switching action is achieved with 7% amplification in the data signal at a central wavelength of 1.55 µm with a maximum shift of the wavelength of 0.001 µm. The proposed device can be easily implemented in cascade designs of programmable photonic and optical switching circuits. Full article

In this work, we investigated a platform for real-time emulsion droplet detection and size measurement in optofluidic platforms. An 8.2 µm core diameter input optical fiber and a multi-mode Gradient Refractive Index (GRIN) output fiber were integrated into an acrylic microfluidic channel platform consisting of three layers. Water-in-oil emulsions were investigated, since relevant applications have emerged in the recent past for these types of emulsions, such as drug encapsulation as well as droplet-based Polymerase Chain Reaction (PCR) amplification of DNA, among others. The main contribution of this work is in understanding the main physical phenomena (i.e., total internal reflection, refraction, and interference) behind the complex transmittance pattern obtained for these droplets. For this purpose, a frequency domain electromagnetic wave propagation modelling of the structure using the Finite Element Method (FEM) was used along with experimental measurements. Full article

Although the characteristics of the traveling 10-day waves (10DWs) above the middle stratosphere have been well explored, little research has been performed on the counterpart in the troposphere and lower stratosphere (TLS). In the present study, we use radiosonde observations and MERRA-2 data from 2020 to characterize traveling 10DWs in mid-latitudes in the TLS. Single-site observations in both hemispheres show that strong 10DW activities are always accompanied by strong eastward jets (10–13 km). MERRA-2 data indicate that in the troposphere, the eastward-propagating modes with larger wavenumbers, i.e., E3, E4, E5 and E6 are dominant, while in the lower stratosphere, the eastward- and westward-propagating modes with small zonal wavenumbers, e.g., 1 and 2, are dominant. Further research on E3, E4, E5 and E6 modes in the troposphere of both hemispheres shows that all the wave activities are positively correlated to the background zonal wind. The refractive index squared reveals that a strong eastward jet is suitable for these four modes to propagate. However, just above the jet, the eastward wind decreases with altitude, and a thick evanescence region emerges above 15 km. E3, E4, E5 and E6 10DWs cannot propagate upward across the tropopause; as such, this can explain why these four modes are weak or even indiscernible in the stratosphere and above. In the troposphere, E5 10DW at 32° S was the most dominant mode in 2020. A case study of the anomalously strong E5 10DW activity on 12 May 2020 indicates that the wave amplification resulted from the upward and equatorward transmission of wave energy flows. Moreover, the tropopause and equatorial region can prevent the propagations of wave energy flows of E5 10DW. The upward-propagating wave energy is deposited near the tropopause, resulting in significant short-term variability in the tropopause height. Full article

Botulinum neurotoxins (BoNT) are the most potent toxins, which are produced by Clostridium bacteria and cause the life-threatening disease of botulism in all vertebrates. Specifically, animal botulism represents a serious environmental and economic concern in animal production due to the high mortality rates observed during outbreaks. Despite the availability of vaccines against BoNT, there are still many outbreaks of botulism worldwide. Alternative assays capable of replacing the conventional in vivo assay in terms of rapid and sensitive quantification, and the applicability for on-site analysis, have long been perused. Herein, we present a simple, highly sensitive and label-free optical biosensor for real-time detection of BoNT serotype C using a porous silicon Fabry–Pérot interferometer. A competitive immunoassay coupled to a biochemical cascade reaction was adapted for optical signal amplification. The resulting insoluble precipitates accumulated within the nanostructure changed the reflectivity spectra by alternating the averaged refractive index. The augmented optical performance allowed for a linear response within the range of 10 to 10,000 pg mL⁻¹ while presenting a detection limit of 4.8 pg mL⁻¹. The practical aspect of the developed assay was verified using field BoNT holotoxins to exemplify the potential use of the developed optical approach for rapid bio-diagnosis of BoNT. The specificity and selectivity of the assay were successfully validated using an adjacent holotoxin relevant for farm animals (BoNT serotype D). Overall, this work sets the foundation for implementing a miniaturized interferometer for routine on-site botulism diagnosis, thus significantly reducing the need for animal experimentation and shortening analysis turnaround for early evidence-based therapy. Full article

Although the angular distribution of noise gratings in holographic photopolymer is understood to arise from Bragg matching, the details of scatter strength and dynamics are not fully understood. This confounds development of materials and recording techniques that minimize haze. Here, the kinetics are studied using a multi-physics numerical approach coupling diffraction of light from the dynamic material including scatter centers, reactions of chemical species initiated by this light, diffusion and swelling of these constituents, and the formation of the refractive index from the resulting composition. The approach is validated in the case of two-beam transmission holography by comparison to traditional harmonic series and rigorous coupled-mode approaches. Two beam holography in the presence of scatter is then used to study haze development. This reveals that haze due to weak noise gratings grows significantly above initial scatter only in reaction-limited materials, consistent with proposed Bragg-matched amplification mechanisms. Amplified haze is found to be proportional to initial scatter, quantifying the impact of clean sample fabrication. Conversely, haze is found to grow super-linearly with sample thickness, illustrating the significant challenge for applications requiring low haze in large thickness. Full article