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.

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.

Red blood cell (RBC) function is significantly altered in sickle cell disease (SCD) due to the polymerization of sickle hemoglobin (HbS) into polymers under deoxygenated conditions leading to the formation of sickle shaped RBCs. Since magnetophoretic mobility is inversely proportional to hemoglobin (Hb) oxygen saturation, we investigated whether magnetophoresis could distinguish RBCs from healthy donors and those from sickle cell patients. Single-cell magnetophoretic mobilities were measured for 4 healthy and 5 SCD samples using cell tracking velocimetry (CTV) under controlled partial pressures of oxygen (pO₂). Preliminary cell separations were also performed using a Miltenyi LS column under air-saturated conditions. The concentrations and magnetophoretic mobilities of the feed, eluted, and captured cell fractions were quantified with a Coulter Counter and CTV. At a pO₂ of 10 mmHg, sickle RBCs showed statistically significant differences in magnetophoretic mobility compared to healthy RBCs, consistent with known differences in oxygen–Hb equilibria. The magnetophoretic mobility reflects the oxygen–Hb equilibrium and can discriminate sickle from healthy RBCs at low pO₂. Separation studies highlight additional complexity in bulk separation under air-saturated conditions, where both magnetism and sickle cell adhesion contribute. These results demonstrate the potential of magnetophoresis to selectively isolate sickle RBCs, which could advance SCD diagnostics, transfusion processing, and research into HbS-containing cells.

Sickle cell disease (SCD) is a complex condition that results in low oxygen affinity and oxidative damage within red blood cells (RBCs), which contributes to serious complications such as vaso-occlusive episodes (VOEs). Given the well-established theoretical and experimental evidence that oxygenated hemoglobin is diamagnetic, whereas deoxygenated hemoglobin and methemoglobin are paramagnetic, this study aims to investigate whether RBCs from patients with SCD exhibit progressively increased magnetic susceptibility in correlation with disease severity. In this study, we employed cell tracking velocimetry (CTV) to perform single-cell analysis of RBC magnetic properties under both oxygenated and deoxygenated states. CTV quantifies the oxygen saturation of each cell by measuring their magnetically induced cell velocities in conjunction with known cell properties. Subsequent statistical analysis revealed that although the mean oxygen saturation of the RBCs from patients with SCD did not differ significantly from that of healthy donors, the magnetic velocities at the 1st and 99th percentile of RBC samples from patients with SCD were significantly reduced and elevated, respectively. These elevated and reduced velocities correlate directly to the magnetic susceptibility of the cell, which corresponds to the hemoglobin state. Moreover, we identified a correlation (P< .01) between magnetic heterogeneity in the top and bottom 1% and pain severity, particularly in patients with SCD experiencing acute VOEs. This study underscores the potential of RBC magnetic properties as biophysical markers for identifying the pain severity in patients with SCD and opening avenues for personalized therapeutic interventions.

The precise isolation and analysis of rare cells from blood are crucial for biomedical research and clinical diagnostics. This review examines recent advancements in magnetic-based separation techniques, focusing on their efficiency in capturing rare cells such as circulating tumor cells (CTCs), circulating fetal cells, and diseased red blood cells (RBCs). These methods use magnetophoresis under external magnetic fields for highly specific isolation with minimal contamination, offering advantages over traditional techniques in speed, cost-effectiveness, and robustness. Magnetic separation is categorized into label-based methods, which use immunomagnetic nanoparticles (IMNs) to target specific cell markers, and label-free methods, which exploit differences in magnetic susceptibility. Both approaches have achieved up to 99% efficiency in isolating diseased RBCs and CTCs. However, challenges remain in improving purity, scalability, and clinical applicability. A key limitation of label-based methods is the need to detach cells from magnetic beads without compromising viability. Label-free technologies, such as magnetic levitation, enable ligand-free separation based on density and susceptibility. Future research should focus on optimizing paramagnetic media, integrating machine learning for enhanced accuracy, and developing high-gradient magnetic fields (~1,000 T/m) to improve efficiency. Advancements in IMNs with stronger magnetic properties will further enhance separation performance, driving clinical translation.