Brennan Grace, Bergamino Silvia, Pescio Martina, Tofail Syed A M, Silien Christophe
Department of Physics and Bernal Institute, University of Limerick, Limerick V94 T9PX, Ireland.
Nanomaterials (Basel). 2020 Dec 4;10(12):2424. doi: 10.3390/nano10122424.
FeO-Au core-shell magnetic-plasmonic nanoparticles are expected to combine both magnetic and light responsivity into a single nanosystem, facilitating combined optical and magnetic-based nanotheranostic (therapeutic and diagnostic) applications, for example, photothermal therapy in conjunction with magnetic resonance imaging (MRI) imaging. To date, the effects of a plasmonic gold shell on an iron oxide nanoparticle core in magnetic-based applications remains largely unexplored. For this study, we quantified the efficacy of magnetic iron oxide cores with various gold shell thicknesses in a number of popular magnetic-based nanotheranostic applications; these included magnetic sorting and targeting (quantifying magnetic manipulability and magnetophoresis), MRI contrasting (quantifying benchtop nuclear magnetic resonance (NMR)-based T and T relaxivity), and magnetic hyperthermia therapy (quantifying alternating magnetic-field heating). We observed a general decrease in magnetic response and efficacy with an increase of the gold shell thickness, and herein we discuss possible reasons for this reduction. The magnetophoresis speed of iron oxide nanoparticles coated with the thickest gold shell tested here (ca. 42 nm) was only ca. 1% of the non-coated bare magnetic nanoparticle, demonstrating reduced magnetic manipulability. The T relaxivity, r, of the thick gold-shelled magnetic particle was ca. 22% of the purely magnetic counterpart, whereas the T relaxivity, r, was 42%, indicating a reduced MRI contrasting. Lastly, the magnetic hyperthermia heating efficiency (intrinsic loss power parameter) was reduced to ca. 14% for the thickest gold shell. For all applications, the efficiency decayed exponentially with increased gold shell thickness; therefore, if the primary application of the nanostructure is magnetic-based, this work suggests that it is preferable to use a thinner gold shell or higher levels of stimuli to compensate for losses associated with the addition of the gold shell. Moreover, as thinner gold shells have better magnetic properties, have previously demonstrated superior optical properties, and are more economical than thick gold shells, it can be said that "less is more".
FeO-Au核壳磁性等离子体纳米颗粒有望将磁响应和光响应结合到一个单一的纳米系统中，促进基于光学和磁性的纳米诊疗（治疗和诊断）联合应用，例如，与磁共振成像（MRI）相结合的光热疗法。迄今为止，等离子体金壳对基于磁性应用中的氧化铁纳米颗粒核心的影响在很大程度上仍未得到探索。在本研究中，我们量化了具有不同金壳厚度的磁性氧化铁核心在一些常见的基于磁性的纳米诊疗应用中的效能；这些应用包括磁性分选和靶向（量化磁操控性和磁泳）、MRI造影（量化基于台式核磁共振（NMR）的T1和T2弛豫率）以及磁热疗（量化交变磁场加热）。我们观察到随着金壳厚度的增加，磁响应和效能普遍降低，在此我们讨论这种降低的可能原因。此处测试的金壳最厚（约42纳米）的氧化铁纳米颗粒的磁泳速度仅约为未包覆的裸磁性纳米颗粒的1%，表明磁操控性降低。厚金壳磁性颗粒的T1弛豫率r约为纯磁性对应物的22%，而T2弛豫率r为42%，表明MRI造影降低。最后，最厚金壳的磁热疗加热效率（固有损耗功率参数）降至约14%。对于所有应用，效率随着金壳厚度的增加呈指数衰减；因此，如果纳米结构的主要应用是基于磁性的，这项工作表明最好使用更薄的金壳或更高水平的刺激来补偿与添加金壳相关的损失。此外，由于更薄的金壳具有更好的磁性，先前已证明具有优异的光学性能，并且比厚金壳更经济，可以说“少即是多”。
