Magnetic nanoparticles enable clinically relevant in vitro diagnosis of β-lactam allergy.

β-lactam antibiotics are the leading cause of drug-induced hypersensitivity reactions. Yet available in vitro diagnostics still show limited sensitivity, specificity and reproducibility. In this work, we report the use of magnetic silica-coated nanoparticles functionalized with dendrimeric antigen conjugates (DeAn@Np) for an improved in vitro detection of β-lactam-specific IgE. These nanoparticles possess a high surface area and combine the chemical versatility of silica with the magnetic properties of iron oxide, enabling efficient magnetic separation and reducing assay handling times compared with centrifugation-based workflows. The chosen nanoparticle size (30 nm) was evaluated in immunoassays using sera from 50 amoxicillin-allergic patients and 44 tolerants, achieving 98% sensitivity and outperforming both conventional RAST (38%) and commercial ImmunoCAP (17%) in this cohort, with sensitivity gains of up to 60% (p < 0.0001). Remarkably, DeAn@Np discriminates effectively between selective and cross-reactive allergic patients, minimizing false positives and negatives with a 100% of specificity compared to conventional RAST (70.4%) (p = 0.005). These results highlight the potential of DeAn@Np as a sensitive and modular platform for β-lactam allergy diagnosis, combining improved analytical performance with practical advantages for future translational immunodiagnostic applications and safer penicillin allergy delabelling. Beyond drug allergy, these modular dendrimer-based magnetic nanoparticles can be extended to other antibody targets, offering a versatile strategy for immunodiagnostic applications.