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A planar waveguide (PW) immunosensor working as a polarisation interferometer was developed for the detection of mycotoxin zearalenone (ZON). The main element of the sensor is an optical waveguide consisting of a thin silicon nitride layer between two thicker silicon dioxide layers. A combination of a narrow waveguiding core made by photolithography with an advanced optical set-up providing a coupling of circular polarised light into the PW via its slanted edge allowed the realization of a novel sensing principle by detection of the phase shift between the p- and s-components of polarised light propagating through the PW. As the p-component is sensitive to refractive index changes at the waveguide interface, molecular events between the sensor surface and the contacting sample solution can be detected. To detect ZON concentrations in the sample solution, ZON-specific antibodies were immobilised on the waveguide via an electrostatically deposited polyelectrolyte layer, and protein A was adsorbed on it. Refractive index changes on the surface due to the binding of ZON molecules to the anchored antibodies were detected in a concentration-dependent manner up to 1000 ng/mL of ZON, allowing a limit of detection of 0.01 ng/mL. Structurally unrelated mycotoxins such as aflatoxin B1 or ochratoxin A did not exert observable cross-reactivity.

The main problem with optical planar waveguide is thermal stress which arises when layers inside the planar waveguide get fused together with different coefficient of thermal expansion (CTE) and due to variation in thermal properties, the problem of thermally induced strain and birefringence occurs inside the waveguide glass layer. In proposed work, the mathematical analysis of thermal induced stress and the thermal strain in waveguide glass layer is calculated. ‘C’ software is used for analysis of an optical planar waveguide to calculate the thermal stress. By using material properties of Invar (64 % iron-36 % nickel alloy) and silicon nitride (Si ) an optical planar waveguide is designed. Here when silicon nitride (Si ) is used as a cladding layer and Invar (64 % iron-36 % nickel alloy) as a core layer in an optical planar waveguide, the problem of birefringence get eradicated as zero thermal stress was achieved.

This work reports on further development of an optical biosensor for the in vitro detection of mycotoxins (in particular, aflatoxin B1) using a highly sensitive planar waveguide transducer in combination with a highly specific aptamer bioreceptor. This sensor is built on a SiO2–Si3N4–SiO2 optical planar waveguide (OPW) operating as a polarization interferometer (PI), which detects a phase shift between p- and s-components of polarized light propagating through the waveguide caused by the molecular adsorption. The refractive index sensitivity (RIS) of the recently upgraded PI experimental setup has been improved and reached values of around 9600 rad per refractive index unity (RIU), the highest RIS values reported, which enables the detection of low molecular weight analytes such as mycotoxins in very low concentrations. The biosensing tests yielded remarkable results for the detection of aflatoxin B1 in a wide range of concentrations from 1 pg/mL to 1 μg/mL in direct assay with specific DNA-based aptamers.

The development of resonance phenomena-based optical biosensors has gained relevance in recent years due to the excellent optical fiber properties and progress in the research on materials and techniques that allow resonance generation. However, for lossy mode resonance (LMR)-based sensors, the optical fiber presents disadvantages, such as the need for splicing the sensor head and the complex polarization control. To avoid these issues, planar waveguides such as coverslips are easier to handle, cost-effective, and more robust structures. In this work, a microfluidic LMR-based planar waveguide platform was proposed, and its use for biosensing applications was evaluated by detecting anti-immunoglobulin G (anti-IgG). In order to generate the wavelength resonance, the sensor surface was coated with a titanium dioxide (TiO2) thin-film. IgG antibodies were immobilized by covalent binding, and the detection assay was carried out by injecting anti-IgG in PBS buffer solutions from 5 to 20 μg/mL. The LMR wavelength shifted to higher values when increasing the analyte concentration, which means that the proposed system was able to detect the IgG/anti-IgG binding. The calibration curve was built from the experimental data obtained in three repetitions of the assay. In this way, a prototype of an LMR-based biosensing microfluidic platform developed on planar substrates was obtained for the first time.

DNA is fundamental for storing and transmitting genetic information. Analyzing DNA or RNA base sequences enables the identification of genetic disorders, monitoring gene expression, and detecting pathogens. Traditional detection techniques like polymerase chain reaction (PCR) and next-generation sequencing (NGS) have limitations, including complexity, high cost, and the need for advanced computational skills. Therefore, there is a significant demand for enzyme-free and amplification-free strategies for rapid, low-cost, and sensitive DNA detection. DNA biosensors, especially those utilizing plasmonic nanomaterials, offer a promising solution. This study introduces a novel DNA-functionalized waveguide-enhanced nanoplasmonic optofluidic biosensor using a nanogold-linked sorbent assay for enzyme-free and amplification-free DNA detection. Integrating plasmonic gold nanoparticles (AuNPs) with a glass planar waveguide (WG) and a microfluidic channel, fabricated through cost-effective, vacuum-free methods, the biosensor achieves specific detection of complementary target DNA sequences. Utilizing a sandwich architecture, AuNPs labeled with detection DNA probes enhance sensitivity by altering evanescent wave distribution and inducing plasmon resonance modes. The biosensor demonstrated exceptional performance in DNA detection, achieving a limit of detection (LOD) of 33.1 fg/mL (4.36 fM) with a rapid response time of approximately 8 min. This ultrasensitive, rapid, and cost-effective biosensor exhibits minimal background nonspecific adsorption, making it highly suitable for clinical applications and early disease diagnosis. The innovative design and fabrication processes offer significant advantages for mass production, presenting a viable tool for precise disease diagnostics and improved clinical outcomes.

Due to the remarkable properties of chalcogenide (Chg) glasses, Chg optical waveguides should play a significant role in the development of optical biosensors. This paper describes the fabrication and properties of chalcogenide fibres and planar waveguides. Using optical fibre transparent in the mid-infrared spectral range we have developed a biosensor that can collect information on whole metabolism alterations, rapidly and in situ. Thanks to this sensor it is possible to collect infrared spectra by remote spectroscopy, by simple contact with the sample. In this way, we tried to determine spectral modifications due, on the one hand, to cerebral metabolism alterations caused by a transient focal ischemia in the rat brain and, in the other hand, starvation in the mouse liver. We also applied a microdialysis method, a well known technique for in vivo brain metabolism studies, as reference. In the field of integrated microsensors, reactive ion etching was used to pattern rib waveguides between 2 and 300 μm wide. This technique was used to fabricate Y optical junctions for optical interconnections on chalcogenide amorphous films, which can potentially increase the sensitivity and stability of an optical micro-sensor. The first tests were also carried out to functionalise the Chg planar waveguides with the aim of using them as (bio)sensors.

Bimetal clad planar waveguide having polyaniline polymer as a guiding layer is proposed and studied for biosensing applications. The dispersion relation and reflectivity of the proposed sensor is obtained using transfer matrix method. The sensing performance and stability of proposed waveguide-based sensor is optimized using different volume fraction of Ag–Au bimetal. The volume fraction 1 represents pure Ag metal coating waveguide that shows maximum sensing performance in our all considered cases. In this case, maximum obtain sensitivity, detection accuracy and quality parameter is 74.140, 11.199 and 559.970°/RIU respectively, at the cover refractive index 1.410. Since, resonance angle and full width at half maxima of resonance peak decreases with increase of Ag metal percentage in Ag–Au bimetal therefore the presence of Au metal decreases the sensing performance of the sensor. Hence, a small volume fraction of Au metal is recommended for higher sensitivity with stability.

Optical printed circuit board (OPCB) waveguide materials and fabrication methods have advanced considerably over the past 15 years, giving rise to two classes of embedded planar graded index waveguide based on polymer and glass. We consider the performance of these two emerging waveguide classes in view of the anticipated deployment in data center environments of optical transceivers based on directly modulated multimode short wavelength VCSELs against those based on longer wavelength single-mode photonic integrated circuits. We describe the fabrication of graded index polymer waveguides, using the Mosquito and photo-addressing methods, and graded index glass waveguides, using ion diffusion on thin glass foils. A comparative characterization was carried out on the waveguide classes to show a clear reciprocal dependence of the performance of different waveguide classes on wavelength. Furthermore, the different waveguide types were connected into an optically disaggregated data switch and storage system to evaluate and validate their suitability for deployment in future data center environments.

The sensing performance of liquid filled prism coupled standard metal clad planar waveguide sensors in presence of transition metal dichalcogenide materials are studied and compared with similar polymer waveguides. For comparison point of view, the film thickness of SiO 2 waveguide and polymer waveguides is so chosen that they have same effective refractive index. The modal equation and other necessary formulae of proposed waveguides are derived using boundary matching technique. Our analysis shows that the sensing performances of both waveguides are improved in presence of an adlayer of transition metal dichalcogenide material. In our all considered 2D materials, monolayer of WS 2 material shows maximum sensitivity and quality parameter for SiO 2 waveguide and WSe 2 material shows maximum sensitivity and quality parameter for polystyrene waveguide. Hence, Tungsten based 2D materials always give better sensing performance than the Molybdenum based 2D material in our all considered cases. Also, the analysis shows that the sensing performance of SiO 2 guiding layer waveguide is better than the polymer guiding layer waveguide. The obtain maximum sensitivity and quality parameter of our proposed SiO 2 waveguide in presence of WS 2 material is 441 0 /RIU and 2138/RIU , respectively.

The Maxwell’s equations are a basic formulation using for solve propagation equations within a waveguide. In this research, the wave propagation inside the waveguide was studied and some basic parameters of wave propagation were measured through MATLAB 2013. Silicon with a refractive index 3.46 was chosen to study this propagation and the use of core and cladding with a lower refractive index 2.46 and some parameters were extracted for the waveguide including propagation constant, cutoff wavenumber, cutoff frequency, cutoff thickness and normalized parameter. These parameters are studied at the wavelength 0.6 μm for transvers electric TE and transvers magnetic TM we changed the core thickness at wavelength constant and found that the number of modes increases as the increase of core thickness and the waveform is thinner in TM than it is in TE. We note from the measurements that the value of cutoff frequency and cutoff thickness are equal in the two types TE and TM. Moreover, when two modes (m=0, 1) and core thickness 0.24 μm the value of propagation constant in TE is equal (34.8901, 30.7737) while in TM (30.6440, 26.1967) respectively, we find that the values in TE are greater than TM. Also, the results obtained from Finite Difference Method were compared with the method used (Maxwell’s equation through wave equation solutions). This work represents a short pathway for the theoretical analysis concerning the electromagnetic waves propagating through Si planar waveguide with both modes (TE and TM) considered.