Synthesis of size-controlled iron oxide nanocubes for MPI-MFH applications Stanley Harvell-Smith, Nguyen T. K. Thanh UCL, UK Magnetic particle imaging (MPI) is a new tracer-based modality which has emerged as a promising tool for many therapeutic and diagnostic applications. 1 Standardly, the tracers employed by MPI are superparamagnetic iron oxide nanoparticles (SPIONs). MPI implements a gradient field with strong gradients and weak field strengths, and the non-linear magnetic response of these SPIONs to the field is detected directly for image generation. Overall performance and imaging quality is greatly influenced by the magnetic properties of the SPION implemented. By improving the properties of SPIONs through tailoring of their physical and chemical characteristics, including the iron oxide core size and shape, it is possible to significantly improve the sensitivity and imaging resolution of MPI. These particles can also be optimised for improved performance in specific MPI applications. The application of interest here is MPI in combination with magnetic fluid hyperthermia (MFH), called MPI-MFH. This refers to MFH performed using the MPI gradient system which permits localised heat deposition to a desired region in biological tissue, mitigating some of the issues with standard MFH application paradigms. The aim is to optimise single-core superparamagnetic iron oxide nanocubes (IONCs) towards both MPI, and MPI-MFH application. Due to their lower spin disorder at the surface and smaller surface anisotropies, IONCs have a greater overall performance in terms of saturation magnetisation and magnetic susceptibility compared to equivalent spherical SPIONs. 2 The effect of changing the core size of spherical SPIONs on MPI performance and sensitivity is well-documented with monodisperse single-core SPIONs having an improved MPI performance up to a magnetic core diameter of ~ 25 nm. 3 With this in mind, an array of IONCs with sizes smaller than 25 nm were synthesised. For good MPI-MFH performance, the nanoparticle must demonstrate impressive MPI spatial resolutions, so heat can be localised more specifically using the MPI gradient field system, and heating performance, individually. Reaction parameters in a thermal decomposition process were altered to obtain decanoic acid-coated magnetite IONCs. In all syntheses, there is clear formation of majority cubic shapes with narrow size distributions. The MFH properties have been measured for the largest and smallest synthesised IONCs. The heating performance for the 7 nm IONCs was poor, with an intrinsic loss parameter (ILP) value of just 0.17 nHm 2 /kg. The ILP value was much larger for the 24 nm IONCs, at 2.71 nHm 2 /kg. The 24 nm size of our IONCs is also close to the optimal size of ~25 nm for MPI, indicating potential application in MPI, and because of the good heating properties, MPI-MFH also. References 1. Harvell-Smith, L. D. Tung, and N. T. K. Thanh, Nanoscale , Advance Article, 2022. 2. M. Bauer,S. F. Situ,M. A. Griswold,and A. C. Samia, Nanoscale , 2016, 8 , 12162-12169 3. W. Tay, D. W. Hensley, E. C. Vreeland, B. Zheng, and S. M. Conolly, Biomed. Phys. Eng. Express , 2017, 3 , 035003.
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