High spin Fe(III)‐doped nanostructures as T₁ MR imaging probes

Abstract

Magnetic Resonance Imaging (MRI) T1 contrast agents based on Fe(III) as an alternative to Gd‐based compounds have been under intense scrutiny in the last 6–8 years and a number of nanostructures have been designed and proposed for in vivo diagnostic and theranostic applications. Excluding the large family of superparamagnetic iron oxides widely used as T2‐MR imaging agents that will not be covered by this review, a considerable number and type of nanoparticles (NPs) have been employed, ranging from amphiphilic polymer‐based NPs, NPs containing polyphenolic binding units such as melanin‐like or polycatechols, mixed metals such as Fe/Gd or Fe/Au NPs and perfluorocarbon nanoemulsions. Iron(III) exhibits several favorable magnetic properties, high biocompatibility and improved toxicity profile that place it as the paramagnetic ion of choice for the next generation of nanosized MRI and theranostic contrast agents. An analysis of the examples reported in the last decade will show the opportunities for relaxivity and MR‐contrast enhancement optimization that could bring Fe(III)‐doped NPs to really compete with Gd(III)‐based nanosystems. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Diagnostic Tools > Diagnostic Nanodevices Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease

Advances in nanoprobes for molecular MRI of Alzheimer's disease

“…This leads to negative/dark contrast on T2w‐MRI. Since iron oxide nanoprobes can also increase T1 signal, they have recently garnered attention as an alternative to Gd‐based agents for T1w‐MRI (Botta et al, 2023). Nanoprobes based on fluorine‐19 ( 19 F) have also been investigated for molecular and cellular imaging using MRI (Mali et al, 2021; Yu, 2013).…”

Naturally biocompatible melanin based iron-complex nanoparticles for pH-responsive magnetic resonance imaging

“…Based on the mechanisms of proton relaxation by paramagnetic metal ions, multinuclear Fecomplexes with increased relaxation involves connecting several iron centers through rigid organic linkers were reported, which could slow molecular rotation [23][24][25]. To improve the unit iron ion concentration in the CAs and cause a significant increase of CAs size, there are some Fe-complex assembled nanoparticles designed to raise the relaxation rate and avoid rapid metabolic excretion [26]. For example, Miao et al used poly-3,4-dihydroxy-L-phenylalanine-b-polysarcosine nanoparticle as carrier to chelate with Fe(III), and the r 1 of obtained CA reaches 5.6 mM −1 s −1 in a 3.0 T magnetic field [27].…”

Liposomal MRI probes containing encapsulated or amphiphilic Fe(iii) coordination complexes

“…Interest in Fe( iii )-based MRI probes has increased recently with several new reports highlighting the challenges of their development as coordination complexes 11,12,14,15,22,23 and in nanostructures. 24…”

“…Interest in Fe(III)-based MRI probes has increased recently with several new reports highlighting the challenges of their development as coordination complexes 11,12,14,15,22,23 and in nanostructures. 24 Our laboratory focuses on the development of transition metal MRI probes, including CEST agents (Fe(II), Co(II) and Ni(II)), 13,25 liposomal CEST agents 26 and relaxivity agents such as high-spin Fe(III) complexes. 12 The development of Fe(III) based agents has many challenges including overcoming low water solubility and lowered relaxivity 12,[27][28][29] and complicated solution chemistry.…”