Libraries of Uniform Magnetic Multicore Nanoparticles with Tunable Dimensions for Biomedical and Photonic Applications

Abstract

Multicore iron oxide nanoparticles, also known as colloidal nanocrystal clusters, are magnetic materials with diverse applications in biomedicine and photonics. Here, we examine how both of their characteristic dimensional features, the primary particle and sub-micron colloid diameters, influence their magnetic properties and performance in two different applications. The characterization of these basic size-dependent properties is enabled by a synthetic strategy that provides independent control over both the primary nanocrystal and cluster dimensions. Over a wide range of conditions, electron microscopy and X-ray diffraction reveal that the oriented attachment of smaller nanocrystals results in their crystallographic alignment throughout the entire superstructure. We apply a sulfonated polymer with high charge density to prevent cluster aggregation and conjugate molecular dyes to particle surfaces so as to visualize their collection using handheld magnets. These libraries of colloidal clusters, indexed both by primary nanocrystal dimension (d p ) and overall cluster diameter (D c ), form magnetic photonic crystals with relatively weak size-dependent properties. In contrast, their performance as MRI T 2 contrast agents is highly sensitive to cluster diameter, not primary particle size, and is optimized for materials of 50 nm diameter (r 2 = 364 mM −1 s −1 ). These results exemplify the relevance of dimensional control in developing applications for these versatile materials.

Magnetic Nanoparticles in Biology and Medicine: Past, Present, and Future Trends

“…Even with these IOP-based molecular MRI techniques, sensitivity is a concern, because accumulation can often be too low to achieve meaningful contrast enhancement [ 85 ]. Current efforts focus on enhancing the magnetic properties of IOP to decrease the effective dose, reducing the associated toxicity and imaging artifacts [ 5 , 73 , 101 ].…”

“…In all cases, external magnetic fields interact with ferrimagnetic nanoparticles that can associate or interact with tissue, cells, or biomolecules allowing for applications from molecular imaging to magnetothermal heating ( Figure 1 ). Superparamagnetic iron oxide nanocrystals (SPIONs) are central to these technologies; these materials ( Figure 1 ) are made from iron oxide, but, because of their small dimensions, they do not exhibit any magnetization unless they are in an external magnetic field [ 5 ]. This is especially desirable for biological applications due to the decreased potential for aggregation in the absence of applied fields [ 6 ].…”

Bioinspired Magnetic Nanochains for Medicine

“…However, one possible solution to this issue is based on the clustering of many superparamagnetic nanocrystals into larger nanoparticles that preserve the superparamagnetic properties, while possessing enhanced magnetic moment that is suitable for effective spatial guidance of the particles in suspension. Therefore, different approaches of superparamagnetic nanoparticle clustering have been proposed in the last two decades, including: one-pot nanoparticle cluster synthesis method, solvothermal methods, chemical cross-linking of nanoparticles in the cluster, preparation of composite nanoparticle clusters with polymers, and emulsion/evaporation-based clustering of hydrophobic nanoparticles, among other strategies ( Figure 6 ) [ 29 , 41 , 42 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 ]. Krasia-Christoforou et al has recently presented an elegant topical review on magnetic nanoparticle clustering that is available for further reading [ 88 ].…”

Sub-second multi-channel magnetic control of select neural circuits in behaving flies

“…4A) which is able to generate a large amount of heat at a low frequency AMF with a high field strength (Ch1: 80 mT; 49.9 kHz). To create the second channel, we used a recently developed iron oxide nanoclusters 23 (Fig. 4B) with a low coercivity to generate a large amount of heat when exposed to a high frequency AMF with a low field strength (Ch2: 12 mT; 555 kHz).…”