The development of carbon-encapsulated iron nanoparticles (CEINS) is of considerable interest in many areas of cancer nanotechnology, ranging from basic tumor biology to early detection and treatment of cancer. To meet these challenges, the present study was undertaken to determine the magnetic and relaxometric performance of CEINS used as a new contrast agent for magnetic resonance imaging (MRI) in preclinical phantom models. CEIN samples were synthesized using a carbon arc discharge route, and the as-synthesized nanoparticles were purified and functionalized with surface acidic groups. The presence of various Fe-bearing metallic phases reflecting the net magnetic properties of CEINS was characterized by powder X-ray diffraction (XRD), thermogravimetry (TGA), and vibrating sample magnetometry. The morphological and surface chemistry features were characterized by electron microscopy (transmission electron microscopy [TEM] and scanning electron microscopy [SEM]), Raman spectroscopy, and Fourier transform-infrared (FT-IR) spectroscopy. The textural properties of CEINS, including porosity, surface total charge density, and zeta potentials, were also measured. The as-synthesized different CEIN samples were finally examined as a potent MRI contrast drug candidate. Magnetic resonance relaxation measurements were performed in bovine gelatin-based phantom models by using a 1.5-T MRI scanner equipped with a standard radiofrequency “birdcage” type head coil. To obtain data, T1- and T2-weighted MR images were acquired using the inversion recovery spin echo (SE) and the SE protocol with multiple time of echo (TE), respectively. Chemical characterization showed similarity in morphology and textural properties between as-synthesized CEINS, purified CEINS, and CEINS functionalized with acidic groups. The as-synthesized CEINS had significantly higher Fe content and higher saturation magnetization. The analysis of the relaxometric properties of CEINS revealed that all the CEIN samples decreased T2 relaxation times on the T2-weighted images. The relaxation rate (1/T2) showed some differences between the as-synthesized, purified, and surface-functionalized CEINS containing surface carboxylic groups. Both the as-synthesized and purified CEINS slightly decreased the T1 relaxation times, which was evident through increase in the relaxation rates (1/T1). This study concludes that CEINS may represent a novel “core-shell”–type negative contrast drug candidate for MRI. It should be emphasized that all the studied CEIN samples have acceptable r2 relaxivities at the field strength of 1.5 T where most of the MRI systems operate in clinical radiology.

从基本的肿瘤生物学到癌症的早期检测和治疗，碳封装的铁纳米颗粒（CEINS）的开发在癌症纳米技术的许多领域都引起了人们的极大兴趣。为了应对这些挑战，本研究旨在确定CEINS作为临床前幻影模型中用于磁共振成像（MRI）的新造影剂的CEINS的磁性和弛豫性能。使用碳弧放电路线合成CEIN样品，然后纯化合成的纳米颗粒并用表面酸性基团进行官能化。通过粉末X射线衍射（XRD），热重分析（TGA）和振动样品磁力分析来表征反映CEINS净磁性的各种含铁金属相。通过电子显微镜（透射电子显微镜[TEM]和扫描电子显微镜[SEM]），拉曼光谱和傅里叶变换红外（FT-IR）光谱对形态和表面化学特征进行表征。还测量了CEINS的质地特性，包括孔隙率，表面总电荷密度和Zeta电位。最终，将合成后的不同CEIN样品作为强效MRI对比药物候选者进行了检查。通过使用配备标准射频“鸟笼”型头线圈的1.5-T MRI扫描仪，在基于牛明胶的幻象模型中进行磁共振弛豫测量。为了获得数据，分别使用反转恢复自旋回波（SE）和具有多次回波时间（TE）的SE协议获取了T1和T2加权MR图像。化学表征在合成的CEINS，纯化的CEINS和用酸性基团官能化的CEINS之间显示出形态和质地特性上的相似性。合成后的CEINS具有明显更高的Fe含量和更高的饱和磁化强度。CEINS弛豫特性的分析表明，所有CEIN样品在T2加权图像上均减少了T2弛豫时间。弛豫速率（1 / T2）在合成的，纯化的和表面官能化的含有表面羧基的CEINS之间显示出一些差异。合成后的CEINS和纯化的CEINS都略微缩短了T1弛豫时间，这通过弛豫率（1 / T1）的增加而明显看出。这项研究得出的结论是，CEINS可能代表MRI的新型“核-壳”型阴性对比药物候选者。