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Monitoring gluten levels in foods labelled as gluten-free or low-gluten — i.e. containing less than 20 ppm and 100 ppm of gluten, respectively — is crucial for preventing celiac disease-related disorders. Due to their inherent complexity, the standard analytical techniques to assess the gluten content in food are not suitable for on-site measurements, whose need is widely recognized. In this context, we developed a rapid and cost-effective biosensor based on core-satellite magnetic particles (CSMPs) — magnetic cores coated with gold nanoparticles (AuNPs) — further functionalized with anti-gliadin antibodies. The study demonstrates that a 0.016% concentration of the surfactant Tween-20 can induce the spontaneous formation of stable CSMP clusters in dispersion. These clusters, composed of weakly interacting functionalized CSMPs, undergo fragmentation in the presence of gliadin, which specifically binds to the antibodies on the CSMPs. This process results in a colour change, which is measurable by a UV–VIS spectrophotometer. Gliadin extraction was achieved by treating the sample with a non-toxic ethanol-water mixture (60%), sufficient to induce a measurable colour change in the presence of gluten contamination, with a limit of detection (LOD) of 8 ppm, which is lower than low limit established for gluten-free food.

Abstract Magneto‐plasmonic particles, comprising gold and iron oxide, exhibit substantial potential for biosensing applications due to their distinct properties. Gold nanoparticles (AuNPs) provide plasmonic features, while iron oxide composites, responsive to an external magnetic field, significantly reduce detection time compared to passive diffusion. This study explores core@satellite magneto‐plasmonic particles (CSMPs), featuring magnetic nanoparticle clusters and numerous satellite‐like AuNPs, to amplify the optical response on a nanostructured gold surface. Using a sandwich scheme, target analytes are detected as hybrid nanoparticles bind to the pre‐immobilized target on the AuNPs surface, inducing changes in the immunosensor's extinction spectrum. Application of an external magnetic field notably enhances biosensor response and sensitivity, reducing assay time from hours to minutes. Leveraging the properties of CSMPs, the immunosensor detects specific immune protein at low concentrations within minutes. CSMPs hold considerable promise for precise and sensitive analyte detection, offering potential applications in rapid testing and mass screening.

We consider extensions of General Relativity based on the non-local function f(R,□−1R), where R is the Ricci curvature scalar and the non-locality is due to the term □−1R. We focus on cosmological minisuperspaces and select viable models by the Noether Symmetry Approach. Then we find viable exact solutions pointing out the role of non-locality in cosmology.

The optical response of different configurations of functionalized gold nanoparticles (f-AuNPs) and SARS-CoV-2 virions is simulated in order to explore the behavior of a colloidal solution containing 105–1013 virions/ml. The analysis herein reported is carried out for three concentration regimes: (i) low (≲108 virions/ml), (ii) intermediate (∼109–1010 virions/ml), and (iii) high (≳1011 virions/ml). Given the high binding effectiveness of f-AuNPs to virions, three different configurations are expected to arise: (i) virions completely surrounded by f-AuNPs, (ii) aggregates (dimers or trimers) of virions linked by f-AuNPs, and (iii) single f-AuNP surrounded by virions. It is demonstrated that 20 nm diameter gold nanoparticles functionalized against all three kinds of SARS-CoV-2 proteins (membrane, envelope, and spike) allow one to reach a limit of detection (LOD) of ∼106 virions/ml, whereas the use of only one kind of f-AuNP entails a ten-fold worsening of the LOD. It is also shown that the close proximity (∼5 nm) of the f-AuNP to the virions assumed throughout this analysis is essential to avoid the hook effect, thereby pointing out the importance of realizing an apt functionalization procedure that keeps thin the dielectric layer (e.g., proteins or aptamers) surrounding the gold nanoparticles.

In the last few decades, plasmonic colorimetric biosensors raised increasing interest in bioanalytics thanks to their cost-effectiveness, responsiveness, and simplicity as compared to conventional laboratory techniques. Potential high-throughput screening and easy-to-use assay procedures make them also suitable for realizing point of care devices. Nevertheless, several challenges such as fabrication complexity, laborious biofunctionalization, and poor sensitivity compromise their technological transfer from research laboratories to industry and, hence, still hamper their adoption on large-scale. However, newly-developing plasmonic colorimetric biosensors boast impressive sensing performance in terms of sensitivity, dynamic range, limit of detection, reliability, and specificity thereby continuously encouraging further researches. In this review, recently reported plasmonic colorimetric biosensors are discussed with a focus on the following categories: (i) on-platform-based (localized surface plasmon resonance, coupled plasmon resonance and surface lattice resonance); (ii) colloid aggregation-based (label-based and label free); (iii) colloid non-aggregation-based (nanozyme, etching-based and growth-based).