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.

Protein rotational kinetics are essential for understanding macromolecular behavior in crowded environments, yet measuring these dynamics at solid-liquid interfaces remains a significant challenge due to low signal strengths. Here, we experimentally demonstrate a label-based optical technique for measuring rotational diffusion kinetics using an all-dielectric multilayer stack that sustains both transverse electric and transverse magnetic polarized surface electromagnetic waves. We introduce the concept of Fluorescence Recovery after Orientational Photobleaching, a rotational analogue to the standard translatory fluorescence recovery after photobleaching technique, which utilizes anisotropic photobleaching via resonant transverse electric excitation followed by real-time monitoring of the orientational relaxation towards isotropy. Our ratiometric analysis of the transverse electric and magnetic polarized fluorescence components allows for a distance-independent estimation of the rotational friction coefficient. Applying this method to covalently bound neutravidin, we observe a rotational friction coefficient (about 5.8E-18 J s) significantly higher than in bulk solutions, highlighting the impact of surface anchoring and molecular crowding. The proposed approach provides a robust, high-sensitivity platform for resolving biomolecular dynamics in complex interfacial environments.

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 detection of water and food contaminants is contributing to reach the Global Goals and the 2030 Agenda for Sustainable Development (especially Goal 2 “Zero hunger” and Goal 6 “Clean water and sanitation”: ensure availability and sustainable management of water and sanitation for all). The widespread presence of contaminants has created an urgent need for analytical tools that are sensitive, specific, accurate, rapid, and easy-to-use to support legislative efforts and enable early warnings. Optical biosensors have emerged as powerful alternatives to traditional methods, which are often time-consuming and labor-intensive. Herein, we review the recent advances in the development of biosensors based on several optical techniques for the detection of food and water contaminants. In our excursus, all the main classes of biological and biomimetic recognition elements are presented ranging from traditional antibodies and molecularly imprinted polymers to DNAzyme and nanobodies. Through a critical analysis of the latest optical biosensor innovations, we explore their current limitations and potential, emphasizing the need to transition these strategies from research to practical applications. This work highlights the synergy of sensing mechanisms, nanomaterials, and technologies in creating advanced optical devices that are cost-effective, miniaturized, accurate, multi-parameter, and integrated, with the goal of bridging the gap between laboratory research and market-ready solutions.

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.

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.

This study explores the potential of Bloch surface waves (BSWs) at the interface of a finite one-dimensional photonic crystal (1D-PC) and vacuum, exploiting spectroscopic ellipsometry in a range that encompasses the mid-infrared (4000 cm-1 to 200 cm-1). BSWs can be excited in both σ and π polarizations, which in the ellipsometric configuration can be detected at the same time, presenting distinct advantages for sensor applications targeting the growth of thin solid films and molecular monolayers, surface-adsorbed gas molecules, and liquid droplets. Compared to other sensing techniques exploiting mid-infrared vibrational absorption lines for chemical-specific sensitivity, like waveguides, nano-antenna arrays, metasurfaces, attenuated total reflectance (ATR) in crystals or in optical fibers, the present approach features high field enhancements, strong field confinement, and large quality factors of the resonances, all while relying on a rather simple and potentially low-cost configuration. The 1D-PCs were fabricated by depositing alternated homogeneous layers out of CaF2 and ZnS with a geometry tailored to sustain BSW with a suitable dispersion in the 5000 cm-1 to 1250 cm-1 range. For the first time to our knowledge, we report the characterization of a sensor based on BSWs in the mid-infrared region using an ellipsometric approach to detect complex reflectivity. Our spectral analysis of mid-infrared 1D-PCs showed clear signatures of σ and π-polarized BSWs and guided modes. Although preliminary, our approach could lead to the development of innovative sensors, enhancing the capabilities of IR ellipsometry by utilizing BSWs in 1D-PCs.

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.

BackgroundDuring targeted treatment, HER2-positive breast cancers invariably lose HER2 DNA amplification. In contrast, and interestingly, HER2 proteins may be either lost or gained. To longitudinally and systematically appreciate complex/discordant changes in HER2 DNA/protein stoichiometry, HER2 DNA copy numbers and soluble blood proteins (aHER2/sHER2) were tested in parallel, non-invasively (by liquid biopsy), and in two-dimensions, hence HER2-2D.MethodsaHER2 and sHER2 were assessed by digital PCR and ELISA before and after standard-of-care treatment of advanced HER2-positive breast cancer patients (n=37) with the antibody-drug conjugate (ADC) Trastuzumab-emtansine (T-DM1).ResultsAs expected, aHER2 was invariably suppressed by T-DM1, but this loss was surprisingly mirrored by sHER2 gain, sometimes of considerable entity, in most (30/37; 81%) patients. This unorthodox split in HER2 oncogenic dosage was supported by reciprocal aHER2/sHER2 kinetics in two representative cases, and an immunohistochemistry-high status despite copy-number-neutrality in 4/5 available post-T-DM1 tumor re-biopsies from sHER2-gain patients. Moreover, sHER2 was preferentially released by dying breast cancer cell lines treated in vitro by T-DM1. Finally, sHER2 gain was associated with a longer PFS than sHER2 loss (mean PFS 282 vs 133 days, 95% CI [210-354] vs [56-209], log-rank test p=0.047), particularly when cases (n=11) developing circulating HER2-bypass alterations during T-DM1 treatment were excluded (mean PFS 349 vs 139 days, 95% CI [255-444] vs [45-232], log-rank test p=0.009).ConclusionsHER2 gain is adaptively selected in tumor tissues and recapitulated in blood by sHER2 gain. Possibly, an increased oncogenic dosage is beneficial to the tumor during anti-HER2 treatment with naked antibodies, but favorable to the host during treatment with a strongly cytotoxic ADC such as T-DM1. In the latter case, HER2-gain tumors may be kept transiently in check until alternative oncogenic drivers, revealed by liquid biopsy, bypass HER2. Whichever the interpretation, HER2-2D might help to tailor/prioritize anti-HER2 treatments, particularly ADCs active on aHER2-low/sHER2-low tumors.Trial registrationNCT05735392 retrospectively registered on January 31, 2023 https://www.clinicaltrials.gov/search?term=NCT05735392

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.

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.

The study of the interaction of fibronectin and phosphorylcholine molecules with surfaces is of high relevance to understand the biological performance of bioactive coatings. To accomplish this task, one-dimensional photonic crystals supporting Bloch surface waves were interrogated in label-free and enhanced fluorescence operation modes. In particular, the enhanced fluorescence mode offers the possibility to confirm the presence of proteins with a sharp improvement of the resolution. Bioactive coatings based on fibronectin/ phosphorylcholine have thus the potential to not only enhance the body acceptance of implanted devices, but also extend the lifetime of such devices.

The growing need for new and reliable surface sensing methods is arousing interest in the electromagnetic excitations of ultrathin films, i.e., to generate electromagnetic field distributions that resonantly interact with the most significant quasi-particles of condensed matter. In such a context, Bloch surface waves turned out to be a valid alternative to surface plasmon polaritons to implement high-sensitivity sensors in the visible spectral range. Only in the last few years, however, has their use been extended to infrared wavelengths, which represent a powerful tool for detecting and recognizing molecular species and crystalline structures. In this work, we demonstrate, by means of high-resolution reflectivity measurements, that a one-dimensional photonic crystal can sustain Bloch surface waves in the infrared spectral range from room temperature down to 10 K. To the best of our knowledge, this is the first demonstration of infrared Bloch surface waves at cryogenic temperatures. Furthermore, by exploiting the enhancement of the surface state and the high brilliance of infrared synchrotron radiation, we demonstrate that the proposed BSW-based sensor has a sensitivity on the order of 2.9 cm-1 for each nanometer-thick ice layer grown on its surface below 150 K. In conclusion, we believe that Bloch surface wave-based sensors are a valid new class of surface mode-based sensors for applications in materials science.

We propose a rapid serologic test based on disposable nano-photonic biochips for SARS-CoV-2 related antibodies. The label-free sensograms showed that positive and negative human serum samples were discriminated, enabling real-time and fast label-free detection.

Human epidermal growth factor receptor 2 (HER2) over-expression occurs in 15–20% of breast cancers and it is generally associated with a dismal prognosis. In this work, we report on the use of one-dimensional photonic crystal biochips to detect clinically relevant concentrations of HER2 in human plasma samples. To this aim, we optimized an optical read-out system, combining both label-free and fluorescence detection, which makes use of biochips tailored with specific proteins for specific biological recognition. Our biochips were used to discriminate HER2 positive/negative human plasma samples providing a solid and reliable tool for clinical diagnostics.

In the last decade, among the various cerebral ischemia biomarkers, microRNAs (miRNAs, MW 7-10 kDa) have recently attracted the attention of researchers. These are short endogenous biomolecules of noncoding ribonucleic acids that negatively regulate gene expression. The presence of miRNAs in blood and the ability to measure their level in a non-invasive way, the so-called liquid biopsy approach, has opened new doors in the search for peripheral biomarkers for the diagnosis and prognosis of diseases such as hemorrhagic stroke. In order to perform liquid biopsy, Bloch surface waves supported by one dimensional photonic crystals are exploited to enhance and redirect the fluorescence arising from a sandwiched miRNA recognition assay. Besides, the sensing elements consist of disposable and low-cost plastic biochips coated with a 1DPC. The assay format consists of a first partial hybridization of an oligonucleotidic probe, immobilized onto the 1DPC surface in five regions, with the miRNA target (miR-16-5p, hemorrhagic stroke biomarker) to be revealed in a complex biological medium. The protocol is then completed with a second partial hybridization of the miRNA target with a second synthetic oligonucleotide conjugated with an organic dye. This last step permits to specifically introduce fluorescence where the sandwich assay is accomplished. Thanks to the present technique, we are able to detect miRNA target solutions with a limit of detection of 32 ng/mL in less than 60 minutes. In conclusion, since the recommended therapeutic window is very limited, biomarkers for cerebral ischemia/hemorrhage have the potential to speed-up diagnosis and the assignment of treatments.