Buruli ulcer (BU), a necrotizing skin disease caused by Mycobacterium ulcerans, remains a neglected tropical disease with complex environmental and vector-mediated transmission dynamics. Motivated by the potential interaction between chronic BU infection, environmental contamination, and cancer-associated immunosuppression, this study develops an integrated mathematical model describing the coupled dynamics of Buruli ulcer and BU–cancer co-infection. The proposed framework incorporates dual transmission pathways, an environmental infectious reservoir, and immunosuppression-mediated progression to the co-infected class. The basic reproduction number [Formula: see text] is derived using the next-generation matrix approach, and the local and global stability properties of the disease-free and endemic equilibria are investigated. Bifurcation analysis is performed to examine threshold behavior near [Formula: see text], while numerical simulations are used to illustrate the qualitative dynamics of the model under representative baseline parameter values. Global sensitivity analysis based on the Latin Hypercube Sampling–Partial Rank Correlation Coefficient (LHS–PRCC) method identifies the environmental contamination rate, Buruli ulcer recovery rate, and progression to the co-infected compartment as the parameters exerting the greatest influence on disease dynamics. The proposed framework provides theoretical insights into the interaction between environmental persistence, Buruli ulcer transmission, and cancer-associated immunosuppression, and may serve as a basis for future epidemiological investigations and model refinement.
A hybrid metasurface absorber (MSA) based on a central-bar-coupled split-disk dimer is proposed and numerically investigated for high-resolution refractive-index sensing in the near-infrared spectral region. The metasurface consists of silicon nitride dielectric resonators integrated with a gold plasmonic layer, enabling strong electromagnetic confinement, enhanced light-matter interaction, and ultra-narrow resonant features within the 1000-1400 nm wavelength range. The optimized structure supports multiple resonant modes under both x- and y-polarized excitation, producing sharp reflection dips with full-width-at-half-maximum values as low as 0.58 nm and quality factors reaching 2007. Refractive-index sensing performance was evaluated by varying the aqueous superstrate refractive index from 1.33 to 1.35, resulting in bulk sensitivities up to 860 nm/RIU under normal incidence. The angular response was further analyzed for incidence angles up to 5°, revealing polarization-dependent resonance splitting and the emergence of additional high-Q resonant branches under oblique excitation. Several angularly induced resonances exhibit narrower linewidths than those observed at normal incidence while preserving high refractive-index sensitivity up to 870 nm/RIU. Electric-field distributions confirm strong field localization near the dielectric boundaries and coupling regions, validating the hybrid resonant mechanism responsible for the enhanced spectral selectivity and sensing performance. The proposed MSA provides a promising platform for compact and ultrasensitive biosensing applications.
Melatonin is a hormone that plays a role in the regulation of circadian rhythms and is also recognized for its antioxidant and cytoprotective functions. Its determination in biological samples is analytically challenging because the physiological concentration is very low, especially in saliva. Here, a competitive immunoassay based on a quartz crystal microbalance (QCM) biosensor was developed for melatonin determination. The biosensor employed a surface modified with a melatonin-albumin conjugate and a multilayer antibody amplification scheme to enhance the piezoelectric response. The assay was calibrated in the low picogram per liter range and provided a limit of detection of 0.55 pg/mL (2.37 pmol/mL) for a 25 µL sample. The analytical performance was sufficient for the determination of physiological melatonin concentrations in saliva and blood. The assay showed satisfactory selectivity against selected potential interferents and correlated strongly with a standard ELISA method, with a coefficient of determination of r2 = 0.994. Application to authentic human saliva samples confirmed the practical utility of the method, and the prepared biosensors remained stable for at least 140 days. The proposed QCM immunoassay represents a simple and sensitive alternative to conventional melatonin assays and demonstrates the potential of piezoelectric biosensing for non-invasive hormone monitoring.
Shigella is a foodborne bacterial pathogen with a low infectious dose and significant public health impact. Culture-based and molecular techniques provide reliable identification but are time-consuming. Nanoparticle-based biosensors offer sensitive, selective, and compact alternatives. Recent advances in nanoparticle-based biosensors for Shigella spp. (S. flexneri, S. sonnei, S. dysenteriae, and S. boydii) detection have been reviewed in terms of signal amplification, biorecognition, biological targets, sensor types, and performance in real food matrices. Detection strategies rely on gene-level and whole-cell recognition. Targeting virulence genes, invasion plasmid antigen H (ipaH), provides stable genus-level identification, whereas whole-cell recognition facilitates rapid detection without extensive sample preparation. Optical biosensors, including fluorescence-based methods, surface-enhanced Raman spectroscopy (SERS), and localized surface plasmon resonance (LSPR), achieve low detection limits with strong tolerance to complex food matrices. Electrochemical biosensors offer operational simplicity, portability, and suitability for food screening. Lateral flow and hybrid systems provide rapid detection through simplified assay formats and visual readout, with performance influenced by the balance between speed and sensitivity. Validation in real food matrices shows acceptable recoveries, minimal cross-reactivity, and agreement with reference methods. This overview provides a design-oriented framework for nanoparticle-based biosensor selection in food safety by integrating nanomaterial function, biosensor design, and performance characteristics.
Virus-specific antibody responses, including binding antibodies and neutralizing antibodies (nAbs), are important indicators of antiviral immune status after infection or immunization. They provide complementary information on antiviral humoral immunity after infection or vaccination. Antigen-binding antibodies indicate previous exposure and the magnitude of the immune response, whereas receptor-blocking and functional neutralization assays assess whether antibodies interfere with viral entry or infection. Conventional neutralization assays, such as plaque reduction neutralization tests and pseudovirus neutralization tests, provide functional information but are labor-intensive, time-consuming, biosafety-restricted, and difficult to deploy for large-scale or decentralized monitoring. Paper-based biosensors, including lateral flow assays (LFAs), microfluidic paper-based analytical devices (μPADs), and paper-based ELISA, have emerged as promising point-of-care tools owing to their low cost, portability, simple operation, and compatibility with visual or digital readouts. This review critically evaluates these platforms according to whether they measure antigen-binding antibodies, receptor-blocking activity, surrogate neutralization, or functional neutralization and summarizes the applications of these three platforms for monitoring antibody responses against SARS-CoV-2, influenza, dengue, Zika, and monkeypox viruses. Unlike previous reviews that mainly focus on general paper-based biosensor design or conventional nAb assays, this review emphasizes the distinction between antigen-binding, receptor-blocking, and surrogate neutralization readouts, and critically discusses how paper-based signals should be interpreted in relation to functional immunity. We further analyze key translational challenges, including quantitative accuracy, antigen cross-reactivity, standardization, clinical validation, regulatory positioning, and real-world implementation. Future development should combine multiplex detection, standardized calibration, digital and AI-assisted interpretation, and clinically validated assay formats. Paper-based biosensors have considerable potential for decentralized antibody monitoring and public health surveillance, but their clinical utility depends on clear assay positioning and validation against appropriate functional or reference methods.
