Magnetoelectric Core–Shell Nanoparticles for Biomedical and Bioelectronic Applications: Materials, Transduction Mechanisms, Surface Engineering, and Translational Perspectives

Magnetoelectric materials couple magnetic and electrical order parameters and can convert remotely applied magnetic fields into localized electrical responses. At the nanoscale, this functionality is commonly pursued through core–shell architectures in which a magnetostrictive or magnetic core is mechanically coupled to a piezoelectric or ferroelectric shell. The resulting strain-mediated transduction is attractive for biomedical and bioelectronic applications because magnetic fields penetrate biological tissue with comparatively low attenuation, whereas the generated electrical signals can interact directly with charged biomolecules, cell membranes, ion channels, and electroactive tissues. This review critically evaluates magnetoelectric core–shell nanoparticles from a broad biomedical and bioelectronic perspective. The physical basis of direct and converse magnetoelectric coupling is first discussed, with emphasis on nanoscale boundary conditions, magnetic-domain state, ferroelectric polarization, interfacial strain transfer, ionic screening, and nonlinear field dependence. Representative magnetic-core/piezoelectric-shell material families, including ferrite-based, multiferroic-oxide, lead-free piezoelectric, PZT-containing, and polymer-integrated architectures, are compared in terms of magnetic response, piezoelectric activity, chemical stability, biocompatibility, toxicity, and processability. Particular attention is given to CoFe2O4–BaTiO3 (CFO-BTO) as a benchmark magnetoelectric core–shell system, while alternative material combinations are comparatively discussed to reflect the broader diversity of the field. Synthesis and processing strategies, structural and physicochemical characterization, surface engineering, and local or macroscopic magnetoelectric measurement methods are examined together with the artifacts that can complicate quantitative interpretation. Particular attention is paid to particle size, shell thickness, crystallinity, aggregation, colloidal stability, surface chemistry, biomolecular functionalization, and their influence on magnetoelectric performance and biological interactions. The available literature demonstrates substantial progress in magnetically triggered drug delivery and cancer therapy, wireless neural and cardiac stimulation, tissue engineering, immunomodulation, wound healing, multimodal imaging, and related bioelectronic applications. Biosensing is also considered an important emerging direction; however, direct quantitative detection of proteins, nucleic acids, pathogens, and cancer biomarkers using isolated core–shell magnetoelectric nanoparticles remains comparatively underdeveloped. The review therefore distinguishes experimentally established biomedical and bioelectronic functionalities from less mature biosensing concepts and identifies the measurement, safety, clinically relevant magnetic-field exposure, scalable manufacturing, device-integration, and regulatory challenges that must be addressed for translation. A practical roadmap is proposed for developing reproducible, lead-free, biologically stable, and quantitatively characterized magnetoelectric nanoparticle platforms for next-generation wireless biomedical and bioelectronic technologies.