This study presents a rigorous comparative analysis of two label-free optical biosensing platforms, Bloch surface wave (BSW) and microring resonator (MRR), for the detection of SARS-CoV-2 antibodies in human serum. To ensure direct comparability, a new BSW readout system was established alongside an existing MRR platform, allowing assays to be conducted under nearly identical experimental conditions. Both sensors were functionalized with various SARS-CoV-2 Spike and Nucleocapsid protein variants to capture specific host antibodies. The results demonstrate that both platforms provide rapid, quantitative, and sensitive detection of anti-Spike and anti-Nucleocapsid antibodies without the need for secondary labels. Furthermore, the platforms show excellent agreement with longitudinal serology benchmarks and high repeatability across different biochip batches. This work establishes both BSW and MRR technologies as powerful, low-cost candidates for next-generation clinical diagnostics and serological surveillance.

Surface functionalization plays a decisive role in the performance of biosensors, as it governs the efficiency and stability of biomolecule immobilization at the sensor interface and, consequently, the overall performance of the biosensing platforms. In this work, we present a comparative study of three organosilane chemistries - APTES, APDMS, and CPTES - applied to a SiO2 terminated 1D photonic crystal able to sustain Bloch surface waves and designed to operate as optical biosensors in both label free and fluorescence enhanced modes. Each chemistry was evaluated through a standardized label-free protocol based on the interaction between immobilized SARS CoV 2 spike protein and its corresponding antibodies, enabling quantitative assessment of binding efficiency, nonspecific adsorption, and signal repeatability. CPTES exhibited the most favorable balance between specific signals, reduced variability, and low nonspecific adsorption. The three chemistries were subsequently tested in fluorescence mode for the detection of anti SARS CoV 2 IgG antibodies in human serum, demonstrating the suitability of BSW enhanced fluorescence for rapid serological analysis. Overall, the study identifies CPTES as the most robust and reproducible functionalization strategy among the three investigated for BSW biosensing and highlights the potential of the platform for fast, sensitive detection of clinically relevant antibodies.

Surface functionalization is a pivotal step in the development of biosensors, as it directly influences the immobilization efficiency of biological recognition elements and, consequently, the overall performance of the biosensing platforms. In this study, we employed the Taguchi method to systematically optimize the functionalization parameters of a silicon oxide surface using an organosilane compound. The biosensing platform is based on a one-dimensional photonic crystal structure capable of sustaining Bloch surface waves, which enable highly sensitive optical detection. The use of the Taguchi orthogonal array design allowed us to efficiently explore a limited and representative set of parameter combinations, significantly reducing experimental complexity. Once the optimal functionalization conditions were identified, the biosensors were applied to the analysis of human serum samples (diluted 1:50) collected from both COVID-19 patients and healthy individuals. The system demonstrated the ability to specifically detect IgM antibodies related to SARS-CoV-2 virus, which are typically present in trace amounts. This work presents the first Taguchi-based optimization of a surface functionalization strategy via label-free molecular interactions for biosensing. The approach provides a platform for both optimization and sensitive detection of clinically relevant biomarkers, with clear diagnostic potential.

Alzheimer's disease (AD) is a progressive neurological disorder that gradually impairs all cognitive functions. The diagnosis typically requires a combination of cognitive assessments, neuroimaging techniques, and biomarker analysis. In healthy neurons, Tau protein stabilizes microtubules, which are vital for maintaining the structure and proper functioning of nerve cells. However, elevated levels of Tau in cerebrospinal or other body fluids can be related to the progression of Alzheimer's disease. This study introduces an optical technique that employs a dual label-free and fluorescence operation mode to detect Tau protein in both standard running buffer and cerebrospinal fluid. This innovative method enables label-free analysis of the bio-conjugation process on biochips used for resolved fluorescence-based Tau detection. This work successfully demonstrates Tau protein detection in both matrixes, achieving an outstanding limit of detection of 2.4 pM in cerebrospinal fluid. Moreover, the analysis of the dose-response curve allows to estimate the dissociation constant (K-D = 18 nM) for Tau interactions, yielding values that are in excellent agreement with existing literature using other techniques. These aspects highlight the added value of this technique, providing a valuable tool for investigating Alzheimer's-related biomarkers, as demonstrated in this study with Tau protein.

The emergence of Coronavirus Disease in 2019, driven by the novel pathogen SARS-CoV 2, has posed a profound challenge to global health. In this context, we employed a combined label-free and fluorescence-based approach to investigate the interaction between two forms of the SARS-CoV-2 spike protein: the receptor-binding domain and the trimeric form. This study utilized one-dimensional photonic crystals supporting Bloch surface waves as optical biosensors. Through the analysis of label-free signals from spike protein probes and ACE-2 molecules, crucial data were gathered, including surface mass coverage and molecular density. The adaptability of this method holds great potential for advancing diagnostic tools and enhancing the understanding of disease biomarkers. These findings provide novel insights into the molecular interactions at the core of the COVID-19 pandemic, deepening our knowledge on the receptor-binding processes involved during SARS-CoV-2 outbreak.

Two-dimensional transition metal dichalcogenides (TMDs) like WS2 and WSe2 demonstrate strong light-matter interactions, including exciton formation, pronounced photoluminescence, and enhanced second-harmonic generation. Van der Waals epitaxy allows for the growth of these semiconducting monolayers on diverse substrates with minimal lattice mismatch effects, enabling scalable integration into photonic integrated circuits (PICs). Encapsulation in tailored dielectrics not only optimizes optical coupling for atomically thin TMDs but also can shield them from environmental degradation. This study systematically investigates thin and scalable dielectric encapsulation for CVD-grown WS2 and WSe2, focusing on their impact on material structure, excitonic behavior, and nonlinear optical response. A range of oxide thin films (SiO2, Al2O3, and TiO2) and deposition methods (atomic layer deposition-ALD and physical vapor deposition-PVD) compatible with PIC foundry technology are explored. Oxide growth rates via ALD and PVD are higher on WS2 surfaces than WSe2, though faster growth can lead to reduced uniformity. While the thin oxide encapsulation has minimal effect on the phonon spectra of WS2 and WSe2, it enhances second-harmonic efficiency as oxide surface roughness increases. WSe2 exciton spectra remain largely unaffected, whereas WS2 excitonic peaks broaden and redshift with higher oxide dielectric constants. This study emphasizes the potential and key considerations for incorporating CVD-grown WS2 and WSe2 into foundry-ready thin dielectrics for photonic applications, confirming that these TMD materials remain stable and controllable under the applied processes. (c) 2025 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

In this study, we present an innovative approach for the detection of Tau protein, a key biomarker of Alzheimer disease, using enhanced fluorescence detection. The methodology utilizes a bio-conjugation process to adapt 1D photonic crystal surface for precise molecular recognition. Our results demonstrate the successful detection of Tau protein in a simple environment, with a detection limit of 0.5 ng/mL and a quantification limit of 1.2 ng/mL. This work introduces optical disposable biochips as a novel diagnostic tool for Alzheimer disease and related neurodegenerative disorders, addressing critical challenges in biomarker detection and paving the way for advancements in therapeutic development.

Accurate and sensitive antibody detection remains critical for advanced COVID-19 diagnostics and monitoring SARS-CoV-2 immunity. This study presents a highly sensitive technique for detecting anti-SARS-CoV-2 antibodies in human serum using an integrated photonic sensing platform. The platform utilizes disposable one-dimensional photonic crystal biochips engineered to sustain Bloch Surface Waves. The biochips are integrated into a custom-made optical set-up, which is capable of dual-mode detection: label-free refractometry and label-based fluorescence. Tests on human serum, including negative controls and positive samples from a recovered COVID-19 patient, confirmed the platform’s effective performance. In fluorescence mode, clear discrimination between positive and negative samples was achieved down to a 1:104 serum dilution, with an optimal operating range centered around 1:103 dilution. These results demonstrate the potential of the technique as a highly sensitive and versatile platform for antibody detection, with significant relevance for advanced COVID-19 diagnostics.

The overexpression and/or amplification of the HER2/neu oncogene has been proposed as a prognostic marker in breast cancer. The detection of the related peptide HER2 remains a grand challenge in cancer diagnosis and for therapeutic decision-making. Here, we used a biosensing device based on Bloch Surface Waves excited on a onedimensional photonic crystal (1DPC) as valid alternative to standard techniques. The 1DPC was optimized to operate in the visible spectrum and the biosensor optics has been designed to combine label-free and fluorescence operation modes. This feature enables a real-time monitoring of a direct competitive assay using detection mAbs conjugated with quantum dots for an accurate discrimination in fluorescence mode between HER2-positive/ negative human plasma samples. Such a competitive assay was implemented using patterned alternating areas where HER2-Fc chimera and reference molecules were bio-conjugated and monitored in a multiplexed way. By combining Label-Free and fluorescence detection analysis, we were able to tune the parameters of the assay and provide an HER2 detection in human plasma in less than 20 min, allowing for a cost-effective assay and rapid turnaround time. The proposed approach offers a promising technique capable of performing combined labelfree and fluorescence detection for both diagnosis and therapeutic monitoring of diseases.

There is an ongoing critical discussion about whether long-term durability of polymer optics can be guaranteed after passing accelerated tests, as the degradation mechanisms are very complex. Thick scratch resistant antireflective coatings AR-hard and antireflective nanostructured coatings AR-plas had been developed several years ago. The polymer substrates are exposed to plasma emissions and ion bombardment both during coating and structuring. On the other hand, cycloolefin-based polymers may undergo structural changes induced by plasma. For the present study, it was possible to re-examine coated samples a long time after their production. Various AR coatings and different cyclic olefin polymers were re-evaluated in terms of their optical properties and coating adhesion.

Light-absorbing black coatings are indispensable for many different optical applications. Thin-film interference coatings can be flexibly adapted to different wavelengths. To generate an effective (> 99 %) light absorption of an interference coating, the interference effect needs to be combined with a well-defined absorption of the layer's material. On this basis, different black absorber coatings were developed and deposited on optical components for actual applications. A wideband black absorber for 400 -1000 nm wavelength on a space spectrometer slit, a bi-directional black coating for a single wavelength in the VIS, which can be wet-chemically etched for micro-patterning, and a black aperture for NIR and SWIR light on the exit face of a dispersion prism are presented.

Transparent and conductive oxides offer metal-like conductivity and high transmission in the visible spectrum. However, they suffer from reflection losses at the film interface due to their high refractive index. A method for producing an ITO nanostructure through plasma etching in a conventional deposition plant equipped with an APS plasma source is presented, resulting in conductive nanostructures with an effective refractive index as low as 1.3. This nanostructure was combined with an AR coating achieving minimal reflectance while maintaining a conductive surface that enables the removal of surface charges as it is needed in AR coatings for quantum computing applications.

ERBB2 is a member of the tyrosine kinase receptor family, a major cancer driver, and a recognized therapeutic target in many cancers, most importantly breast cancer. Its presence in soluble form in blood correlates with tumor expression and may have implications for diagnostic and therapeutic decisions. Herein, we develop a new approach that makes use of a direct competitive ERBB2 assay and 1-D photonic crystal-based biochips. Such biochips permit to operate in a combined label-free/fluorescence mode enabling ERBB2 biosensing in lysates from selected breast cancer cells, either ERBB2-positive (SK-BR 3, BT474) or ERBB2-negative (T47D). Moreover, our biochips allow the collection of enhanced fluorescence spectra, providing a highly specific ERBB2 detection in the three model cell lines. The main advantage of the assay developed in this work lies in the single-step detection procedure that reduces assay turnaround time to less than 20 min. This latter feature confirms the great potential of the technique in the rapid detection of ERBB2 in complex biological media.

The monitoring of anthropogenic CO2 by satellites (part of Copernicus, the European Union's Earth Observation and Monitoring program) requires a special dispersive spectrometer.As a highly efficient light dispersing element, a Prism-Grating Prism (PG-P) optical element will operate in the program, mentioned above.Anti-reflection (AR) coatings and light blocking apertures are requested to suppress optical losses, to reduce stray light and to shape the beam.Beside the AR-coatings, deposition of "black" aperture as a coating directly on the PG-P element, allows to abstain a mechanical aperture.Thereby, reduced number of elements in the optical setup and therefore reduced payload of the satellite can be achieved.For this purpose, an antireflective coating inside a clear aperture combined with a light blocking and absorbing aperture-coating outside the clear aperture was realized.The developments shown in this contribution were performed for the application wavelength of 1590 -1675 nm.

We present the design, manufacturing and characterization results of a customized high-resolution echelle grating. The grating was manufactured at Fraunhofer IOF and delivered to the NIRPS (Near Infrared Planet Searcher Instrument) consortium. The technology workflow for the manufacturing of the echelle grating is relying on wet-chemical etching, applied to crystalline silicon substrates, which enables the creation of highly determined micro-facets and surfaces over macroscopic dimensions. The echelle’s grating period and plateau size within one period are established based on electron-beam lithography. A binary pattern in a hard mask material is performed by dry-reactive ion etching while transferring the pattern in the silicon substrate is achieved by wet-chemical etching with potassium hydroxide. The grating is designed to operate at a blaze angle of 76° in a wavelength band of 0.9μm – 1.8μm. A gold coating is applied to increase the diffraction efficiency to about 70%; verified at wavelengths of 1030nm and 1640nm, respectively. The overall grating size is 78mm x 284mm providing a WFE of less than 70nm (RMS) measured throughout the full aperture. In this article we present the manufacturing workflow and structural inspection results of the manufactured echelle grating, having a critical eye on the impact of sub-surface defects of the initial silicon crystal. Moreover, we present optical performance test results covering diffraction efficiency, PSF, WFE and spectral ghosts. It is concluded that the imaging properties of the manufactured grating are as good as those of a plane gold mirror reference. Additional presentation content can be accessed on the supplemental content page. Additional presentation content can be accessed on the supplemental content page.

We report on the use of biochips based on one-dimensional photonic crystals sustaining Bloch surface waves to specifically detect target miRNA that is characteristic of hemorrhagic stroke (miR-16-5p) at low concentration in a buffer solution. The biochips were functionalized with streptavidin and ssDNA oligonucleotides to enable miRNA detection. To discriminate the target miRNA from a non-specific control (miR-101a-3p), we made use of an optical platform developed to work both in label-free and fluorescence detection modes. We demonstrate that the limit of detection provided when operating in the fluorescence mode allows us to specifically detect the target miRNA down to 1 ng mL-1 (140 pM), which matches the recommendations for diagnostic miRNA assays, 5 ng mL-1. The low costs open the way towards the application of these disposable optical biochips based on 1DPC sustaining Bloch surface waves as a promising tool for early disease detection in a liquid biopsy format.

This study presents the development and characterization of a disposable biochip for the detection of antibodies against the SARS-CoV-2 spike protein, a well-known target for vaccine and therapeutic development. This biochip is based on a one-dimensional photonic crystal (1DPC) deposited on a plastic substrate and designed to sustain Bloch surface waves (BSW) in the visible range. The experimental phase was carried out using the biochip in conjunction with a custom-made optical read-out platform capable of real-time refractometric detection and fluorescence-based end-point measurements. Our biochip was functionalized by immobilizing the receptor-binding domain of the spike protein onto the surface using a silanization process. Human serum samples, including a negative control and a positive sample from a recovered COVID-19 patient, were tested on the biochip. The experimental results show that the biochip discriminates between positive and negative samples in a label-free refractometric mode down to a 1:10 dilution of the sera and in quantum dot amplified refractometric and fluorescence mode down to 1:100 dilution. The results demonstrate the potential of the disposable biochip for sensitive and specific detection of COVID-19 antibodies.