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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The performance of the metamaterial-inspired substrate-integrated waveguide is discussed in this work, concerning a resonator misalignment potentially caused by the fabrication process. Initially, the design parameters of the aforementioned waveguide at the X-band are presented, while its optimal operation is validated to prove the effectiveness of the apparatus. Then, various significant aspects of the polynomial chaos expansion theory are briefly introduced to facilitate the sensitivity analysis due to fabrication errors. The direction of misalignment is, firstly, investigated, while the general case is, also, considered, highlighting a notable immunity, especially at lower frequencies. Additionally, a parametric examination is conducted in terms of the fabrication tolerance, measured as a percentage of the resonator unit cell. All the required simulations are conducted utilizing the non-intrusive approach of the polynomial chaos methodology via the popular Finite-Difference Time-Domain scheme.

Lossy mode resonance (LMR) has garnered significant attention in sensor applications. LMR was primarily explored in fiber-based systems, however, there has been a recent upsurge in its application within planar waveguides. This article compares the LMR phenomenon in planar waveguides with the most employed coatings in the field, specifically SnO2, TiO2, and ITO. Additionally, the experimental findings are compared with simulations conducted using the finite element method (FEM) within the COMSOL Multiphysics environment. The novelty of this research lies in the integration of both experimental results and theoretical calculations, utilizing strong FEM simulation tools, in a single study.

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.

This paper introduces a novel design of a tapered rib waveguide utilizing Hybrid Chalcogenide material. The waveguide is 4 mm in length and has a core of GAP-Se. GAP-Se is a combination of GeSe2, As2Se3, and PbSe. The upper and lower cladding are made of SiO2. The varying height of the rib layer results in a reduced effective mode area and an increased nonlinear coefficient. To achieve a desirable and intended supercontinuum spectrum in this waveguide, we utilize a pump pulse with a pulse duration of 100 fs and a power of 1 kW at a wavelength of 3.1 µm. We can change the waveguide dimensions to control and engineer the dispersion properties, which give us two zero dispersion wavelengths at 2.81 µm and 4.91 µm. As a result, we get a supercontinuum spectrum from 2.2 to 5 µm with a bandwidth of 2.8 µm. This design can be useful for different purposes such as biomedical, sensors, and optical coherence tomography. [ABSTRACT FROM AUTHOR]

• Fabrication of high energy band gap composite SiO x :TiO y layers of refractive index ca. 1.65. • Resulting composite SiO x :TiO y layers are amorphous and optically homogeneous. • Surface roughness of SiO x :TiO y layers is below 0.2 nm and autocorrelation length is ca. 7 nm. • Elaborated composite SiO x :TiO y waveguide layers have ultra-low optical losses (<0.25 dB/cm). • The influence of SiO x :TiO y waveguide layers surface parameters on optical losses have been determined. This work reports a study on low-loss waveguide layers for planar evanescent wave sensor applications. Crack-free SiO x :TiO y composite layers with refractive indices of ∼1.65, in the visible spectra range, were fabricated using a sol-gel method and a dip-coating technique. Layers of thickness in the 220–360 nm range were produced in a single coating process. By multiple coatings, SiO x :TiO y composite layers of thickness up to 1000 nm were produced. Fabricated layers demonstrated good waveguide properties in the Vis spectral range. The dispersion characteristics of the developed layers refractive index were determined using the spectroscopic ellipsometry method. Spectrophotometric tests validated their optical homogeneity. Using the Tauc method, the widths of optical band gaps were determined, and their high values (E g > 3.7 eV) attest to the amorphous nature of the layer material. The FT-IR studies testified to Si-O-Ti bonds, an attribute of amorphous SiO x :TiO y composites. The tests of surface morphology of the SiO x :TiO y layers, using atomic force microscopy, scanning electron microscopy, and optical profilometry, confirmed their high smoothness. Using the m -line method, waveguide properties and optical losses were examined. To facilitate the interpretation of the experimental results, the mode characteristics and the calculated impact of surface morphology of the waveguide layer. [ABSTRACT FROM AUTHOR]

Sepsis, a life-threatening inflammatory response, demands economical, accurate, and rapid detection of biomarkers during the critical "golden hour" to reduce the patient mortality rate. Here, we demonstrate a cost-effective waveguide-enhanced nanogold-linked immunosorbent assay (WENLISA) based on nanoplasmonic waveguide biosensors for the rapid and sensitive detection of procalcitonin (PCT), a sepsis-related inflammatory biomarker. To enhance the limit of detection (LOD), we employed sandwich assays using immobilized capture antibodies and detection antibodies conjugated to gold nanoparticles to bind the target analyte, leading to a significant evanescent wave redistribution and strong nanoplasmonic absorption near the waveguide surface. Experimentally, we detected PCT for a wide linear response range of 0.1 pg/mL to 1 ng/mL with a record-low LOD of 48.7 fg/mL (3.74 fM) in 8 min. Furthermore, WENLISA has successfully identified PCT levels in the blood plasma of patients with sepsis and healthy individuals, offering a promising technology for early sepsis diagnosis.