Bioapplications of magnetic nanobars: Nanowarming and bioidentification

This chapter discusses the design of magnetic nanobars (MNBs) for optimal rewarming of cryopreserved biospecimens inside alternating magnetic fields (AMF) and also methods to use these same MNBs as in situ labels for specimen identification. MNBs are very short magnetic nanowires (MNWs) with large areas in their hysteresis loops. This area (multiplied by frequency) is the theoretical maximum heating rate that any magnetic material can achieve. Why is it important to start with high theoretical heating rates? The dominant criteria for rewarming cryopreserved specimens are uniform heating (to avoid thermal stress fractures, achieved by well dispersed nanoparticle heaters) and rapid heating (to avoid crystallization, achieved by high heating rates). High heating rates are achieved by rectangular hysteresis loops that have large areas, which are equal to 4 × saturation magnetization (Ms) × coercive field (Hc). That is, high-moment materials with Hc tailored to match the field amplitude of any specific clinically available AMF will convert the most magnetic energy into thermal energy. First, this chapter discusses initial heating experiments and then design of optimal heaters using simulations followed by experimental verification. Second, this chapter explores the possibility to use the MNBs as in situ barcodes for specimens because MNBs will be perfused in and around each specimen as it is cryopreserved. Two techniques are proposed to ID specimens before warming them: magnetometry and ferromagnetic resonance identification (FMR-ID). Magnetometry involves measuring magnetization under a specific sequence of applied magnetic fields to detect the magnetization signatures of each MNB type. FMR-ID involves measuring the absorption of high frequency AC signals during application of DC magnetic fields where the absorption occurs at unique frequency-field pairs for each MNB type. FMR is then shown to enable quality control for as-synthesized MNBs before further processing. A side application Si-integrated vertical vias is briefly introduced. Last but definitely not least, nanoscale iron cobalt (FeCo), iron gallium (FeGa or Galfenol), and Ni have been shown to be more biocompatible than nano-silica. All of these factors clearly enable the prospect of safely and securely rewarming biospecimens.