Magnetic nanoparticles (MNPs) represent a class of small particles typically with diameters ranging from 1 to 100 nanometers. These nanoparticles are composed of magnetic materials such as iron, cobalt, nickel, or their alloys. The nanoscale size of MNPs gives them unique physicochemical (physical and chemical) properties not found in their bulk counterparts. Their versatile nature and unique magnetic behavior make them valuable in a wide range of scientific, medical, and technological fields. Over the past decade, there has been a significant surge in MNP-based applications spanning biomedical uses, environmental remediation, data storage, energy storage, and catalysis. Given their magnetic nature and small size, MNPs can be manipulated and guided using external magnetic fields. This characteristic is harnessed in biomedical applications, where these nanoparticles can be directed to specific targets in the body for imaging, drug delivery, or hyperthermia treatment. Herein, this roadmap offers an overview of the current status, challenges, and advancements in various facets of MNPs. It covers magnetic properties, synthesis, functionalization, characterization, and biomedical applications such as sample enrichment, bioassays, imaging, hyperthermia, neuromodulation, tissue engineering, and drug/gene delivery. However, as MNPs are increasingly explored for in vivo applications, concerns have emerged regarding their cytotoxicity, cellular uptake, and degradation, prompting attention from both researchers and clinicians. This roadmap aims to provide a comprehensive perspective on the evolving landscape of MNP research.

Blood cell separation is a critical process for many clinical and research applications. Among the various techniques employed for blood cell isolation, magnetic techniques are very attractive due to their multiple benefits, i.e. high efficiency, simplicity, low-cost, and no need for expensive equipment or trained operators. Microfluidic devices integrating magnetophoresis have demonstrated promising results for high-throughput separation, with some achieving separation rates of over 10⁸ cells per hour. However, there are many different approaches that can be used for blood magnetic separations, with the selection depending on the sample properties, target cells and purpose of the isolated fractions. This critical review examines recent advances (2014–2025) in magnetic techniques for separating blood cells. Both labeled and label-free approaches are analyzed, with a focus on their performance and impact on cellular function, highlighting their strengths, limitations, and potential for future development in clinical research applications. Among the labeled approaches, positive selection methods have been shown to achieve high purities for various cell types; nevertheless, these techniques might affect cell functionality after separation. Therefore, negative selection can be used for the separation of cells when cellular functionality needs to be preserved. Moreover, label-free techniques, primarily focused on red blood cells (RBCs) separation, can be used for blood cell isolation by leveraging the cells' intrinsic magnetic properties. These methods showed potential for continuous, high-purity RBCs separation, with some devices achieving over 95% recovery and purity. This work aims to provide valuable guidelines for the appropriate selection of magnetic technologies for blood separations to accomplish the successful implementation of magnetophoresis in clinical practice.

Magnetic resonance imaging (MRI) is a non-invasive and non-ionizing imaging modality that provides high-resolution images of internal organs such as the breast, brain, and cardiovascular system, enabling three-dimensional visualization of soft tissues. While MRI offers excellent soft tissue contrast, its sensitivity can be further enhanced using contrast agents, and many clinical applications rely on exogenous agents to improve detection and diagnostic accuracy. Two primary classes are used clinically: paramagnetic substances, exemplified by gadolinium (Gd), which predominantly shorten longitudinal ( T ₁ ) relaxation, and superparamagnetic iron oxide nanoparticles (SPIONs), which exert strong effects on transverse ( T ₂ ) relaxation. The performance and safety of these agents are strongly influenced by their pharmacokinetics and biodistribution, including rapid recognition and clearance by the reticuloendothelial system, which can both enable liver–spleen imaging and limit target-specific contrast in other organs. In this review, we first summarize the fundamental principles of MRI contrast generation, with an emphasis on relaxation mechanisms relevant to magnetic nanoparticles (MNPs). We then discuss the use of MNPs as contrast agents in representative biomedical applications, focusing on cardiac, breast, and brain MRI and illustrating how organ-specific physiology constrains nanoparticle design and performance. Finally, we examine biocompatibility and safety considerations for both Gd-based agents and SPIONs, highlighting current regulatory concerns, open questions regarding long-term toxicity, and key challenges that must be addressed to translate next-generation nanoparticle-based MRI contrast agents into routine clinical practice.

Hematological analysis is crucial for diagnosing and monitoring blood-related disorders. Nevertheless, conventional hematology analyzers remain confined to laboratory settings due to their high cost, substantial space requirements, and maintenance needs. Herein, we present a portable cell tracking velocimetry (CTV) device for the precise measurement of the magnetic susceptibility of biological entities at the single-cell level, focusing on red blood cells (RBCs) in this work. The system integrates a microfluidic channel positioned between permanent magnets that generate a well-defined magnetic field gradient (191.82 TA/mm²). When the cells are injected into the chamber, their particular response to the magnetic field is recorded and used to estimate their properties and quantify their intracellular hemoglobin (Hb) concentration. We successfully track over 400 RBCs per condition using imaging and trajectory analysis, enabling detailed characterizations of their physical and magnetic properties. A comparison of the mean corpuscular hemoglobin measurements revealed a strong correlation between our CTV system and standard ultraviolet–visible (UV-Vis) spectrophotometry (23.1 ± 5.8 pg vs. 22.4 ± 3.9 pg, p > 0.05), validating the accuracy of our measurements. The system’s single-cell resolution reveals population distributions unobtainable through conventional bulk analysis methods. Thus, this portable CTV technology provides a rapid, label-free approach for magnetic cell characterization, offering new possibilities for point-of-care hematological analysis and field-based research applications.

Magnetic nanoparticles (MNPs) that can support both magnetic particle imaging (MPI) and magnetic resonance imaging (MRI) are attractive for dual-modal imaging because they combine the quantitative, background-free tracer detection of MPI with the anatomical contrast of MRI. However, the MPI- and MRI-relevant performance of ferrite nanoparticles is strongly governed by core size, composition, magnetic relaxation, and biological environment. Here, we report a comparative study of four lab-synthesized, quasi-cubic MNP formulations: 30 nm Fe3O4 nanoparticles (F1), 10 nm Fe3O4 nanoparticles (F2), 30 nm Zn0.4Fe2.6O4 nanoparticles (Z1), and 10 nm Zn0.4Fe2.6O4 nanoparticles (Z2). The morphological, physicochemical, cytocompatibility, and cellular uptake properties of these nanoparticles were systematically characterized. Magnetic particle spectroscopy (MPS) was used as an MPI-relevant screening method to compare the dynamic magnetization responses of these nanoparticles under excitation fields in both water and agar phantoms. Z1 produced the strongest mass-normalized harmonic amplitudes under 7.75 kHz excitation in both water and agar phantoms, identifying it as the highest signal formulation for MPI applications. Agar embedding generally reduced the harmonic amplitudes, consistent with restriction of Brownian rotation and demonstrating that physical confinement can strongly affect the MPI-relevant tracer response. Among the 10 nm formulations, Z2 generated stronger absolute harmonic signals than F2 under both conditions and produced the second-highest harmonic amplitudes in the agar phantom. T1-weighted MRI phantom imaging further confirmed concentration-dependent signal attenuation. Z2 and F2 generated more localized hypointense contrast under T1-weighted imaging conditions, while Z1 and F1 generated susceptibility-related signal loss extending beyond the physical boundaries of the inclusions at equivalent nanoparticle concentrations. This spatially extended hypointensity can obscure boundary definition and complicate quantitative signal-intensity analysis. Overall, these findings clarify how core size and Zn substitution regulate the magnetic, biological, MPI-relevant, and MRI-relevant behavior of ferrite nanoparticles and identify Z2 as a promising balanced tracer candidate for dual-modal MPI-MRI imaging.