One potential cancer treatment selectively deposits heat to the tumor through activation of magnetic nanoparticles inside the tumor. This can damage or kill the cancer cells without harming the surrounding healthy tissue. The properties assumed to be most important for this heat generation (saturation magnetization, amplitude and frequency of external magnetic field) originate from theoretical models that assume non-interacting nanoparticles. Although these factors certainly contribute, the fundamental assumption of ‘no interaction’ is flawed and consequently fails to anticipate their interactions with biological systems and the resulting heat deposition. Experimental evidence demonstrates that for interacting magnetite nanoparticles, determined by their spacing and anisotropy, the resulting collective behavior in the kilohertz frequency regime generates significant heat, leading to nearly complete regression of aggressive mammary tumors in mice.

Magnetic nanoparticles can create heat that can be exploited to treat cancer when they are exposed to alternating magnetic fields (AMF). At a fixed frequency, the particle heating efficiency or specific power loss (SPL) depends upon the magnitude of the AMF. We characterized the amplitude-dependent SPL of three commercial dextran-iron oxide nanoparticle suspensions through saturation to 94 kA/m with a calorimeter comprising a solenoid coil that generates a uniform field to 100 kA/m at ∼150 kHz. We also describe a novel method to empirically determine the appropriate range of the heating curve from which the SPL is then calculated. These results agree with SPL values calculated from the phenomenological Box-Lucas equation. We note that the amplitude-dependent SPL among the samples was markedly different, indicating significant magneto-structural variation not anticipated by current models.

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The assembly of magnetic cores into regular structures may notably influence the properties displayed by a magnetic colloid. Here, key synthesis parameters driving the self‐assembly process capable of organizing colloidal magnetic cores into highly regular and reproducible multi‐core nanoparticles are determined. In addition, a self‐consistent picture that explains the collective magnetic properties exhibited by these complex assemblies is achieved through structural, colloidal, and magnetic means. For this purpose, different strategies to obtain flower‐shaped iron oxide assemblies in the size range 25–100 nm are examined. The routes are based on the partial oxidation of Fe(OH)2, polyol‐mediated synthesis or the reduction of iron acetylacetonate. The nanoparticles are functionalized either with dextran, citric acid, or alternatively embedded in polystyrene and their long‐term stability is assessed. The core size is measured, calculated, and modeled using both structural and magnetic means, while the Debye model and multi‐core extended model are used to study interparticle interactions. This is the first step toward standardized protocols of synthesis and characterization of flower‐shaped nanoparticles.