Magnetic core–shell nanowires as MRI contrast agents for cell tracking

Abstract

Background: Identifying the precise location of cells and their migration dynamics is of utmost importance for achieving the therapeutic potential of cells after implantation into a host. Magnetic resonance imaging is a suitable, non-invasive technique for cell monitoring when used in combination with contrast agents. Results: This work shows that nanowires with an iron core and an iron oxide shell are excellent materials for this application, due to their customizable magnetic properties and biocompatibility. The longitudinal and transverse magnetic relaxivities of the core-shell nanowires were evaluated at 1.5 T, revealing a high performance as T 2 contrast agents. Different levels of oxidation and various surface coatings were tested at 7 T. Their effects on the T 2 contrast were reflected in the tailored transverse relaxivities. Finally, the detection of nanowire-labeled breast cancer cells was demonstrated in T 2-weighted images of cells implanted in both, in vitro in tissue-mimicking phantoms and in vivo in mouse brain. Labeling the cells with a nanowire concentration of 0.8 μg of Fe/mL allowed the detection of 25 cells/µL in vitro, diminishing the possibility of side effects. This performance enabled an efficient labelling for high-resolution cell detection after in vivo implantation (~ 10 nanowire-labeled cells) over a minimum of 40 days. Conclusions: Iron-iron oxide core-shell nanowires enabled the efficient and longitudinal cellular detection through magnetic resonance imaging acting as T 2 contrast agents. Combined with the possibility of magnetic guidance as well as triggering of cellular responses, for instance by the recently discovered strong photothermal response, opens the door to new horizons in cell therapy and make iron-iron oxide core-shell nanowires a promising theranostic platform.

Revisiting anodic alumina templates: from fabrication to applications

“…It is also worth to mention the use of such magnetic nanowires, in particular core-shell structured nanowires, in biomedical applications 267 for cell separation 268,269 and tracking 270 , as drug delivery vehicles driven by a magnetic field and hyperthermia treatment 271 .…”

Magnetic Nanomaterials as Contrast Agents for MRI

“…Also considering improvements of the negative contrast in MRI, Martínez-Banderas et al [ 112 ] fabricated distinct, one-dimensional nanostructures composed of an iron core together with an iron oxide shell (Fe-Fe x O y core–shell NWs). Their r 1 , r 2 , and r 2 /r 1 ratio was assessed under a 1.5 T magnetic field; it was observed that they possessed a great potential for this application.…”

A Guideline for Effectively Synthesizing and Characterizing Magnetic Nanoparticles for Advancing Nanobiotechnology: A Review

“…In this direction, Shore et al introduced Fe/Au multi-segmented magnetic nanowires where they observed the shorter segments with larger diameters have significant improved T2 relaxation time [167]. More recently, Martinez-Banderas et al introduced core-shell iron-iron oxide magnetic nanowires with excellent T2 relaxation time suitable for cell tracking [170]. The authors varied the oxidization level of their electrodeposited Fe nanowires and they showed the oxide thickness can be adjusted to tailor the transverse relaxation time.…”