Abstract Superparamagnetic nanoparticles, exposed to an external variable magnetic field, undergo rapid excitation/relaxation. So-called soft magnets, typically iron-based, rapidly and completely relax when the magnetic field returns to zero. Instead, cobalt-based (CoB) hard magnets retain residual magnetization, a characteristic related with the procedure for nanoparticles (NPs) production. Many researchers are still attracted by the potential of CoB NPs for theranostics as multifaced signal probes for imaging, microrobots, enhanced thermo/radiation therapy, and drug release. Since iron oxide NPs are the only magnetic NPs approved for human use, they are of reference for analyzing the potential of the disregarded CoB NPs. In vitro observed toxicity of CoB NPs, largely attributable to cobalt ions and other chemical species released by dissolution, excluded them from further investigations in humans. Nevertheless, experimental evidences documenting the in vivo toxicity of engineered CoB NPs remain very few. The surface functionalization adds newer properties and could improve the biocompatibility of NPs, critical for the clinical exploitation. In our opinion, it would be worth to further exploit the potential of finely tunable properties of CoB NPs in in vivo systems in order to establish a systematic database of properties and effects suitable for human application. Graphical abstract

中文翻译：

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钴磁性纳米粒子作为治疗诊断：可以想象还是可以忘记？

摘要 暴露于外部可变磁场的超顺磁性纳米颗粒会经历快速激发/弛豫。所谓的软磁体，通常是铁基的，当磁场恢复为零时，会迅速完全松弛。相反，钴基 (CoB) 硬磁体保留剩余磁化强度，这是与纳米颗粒 (NP) 生产过程相关的特征。CoB NPs 作为多面信号探针用于成像、微型机器人、增强热/放射治疗和药物释放的潜力仍然吸引了许多研究人员。由于氧化铁 NP 是唯一被批准用于人类使用的磁性 NP，因此它们可作为分析被忽视的 CoB NP 潜力的参考。体外观察到的 CoB NPs 的毒性，主要归因于溶解释放的钴离子和其他化学物质，将它们排除在对人类的进一步研究之外。然而，记录工程化 CoB NPs 体内毒性的实验证据仍然很少。表面功能化增加了新的特性，可以提高 NPs 的生物相容性，这对临床开发至关重要。在我们看来，为了建立适合人类应用的特性和效果的系统数据库，进一步开发 CoB NPs 在体内系统中可微调特性的潜力是值得的。图形概要 在我们看来，为了建立适合人类应用的特性和效果的系统数据库，进一步开发 CoB NPs 在体内系统中可微调特性的潜力是值得的。图形概要 在我们看来，为了建立适合人类应用的特性和效果的系统数据库，进一步开发 CoB NPs 在体内系统中可微调特性的潜力是值得的。图形概要