Table 1.
A summary of the bio-responsive magnetic nanoparticulate systems encompassed in this review. The sizes, changes in relaxivity, stimulus, as well as the advantages of each sytem are included. MMP, matrix metalloproteinase; PAA, poly(acrylic acid); MSN, mesoporous silica nanoparticle; MRI, magnetic resonance imaging; GSH, glutathione.
| Type | Size | Relaxivities | Stimulus | Advantages | Reference |
|---|---|---|---|---|---|
| Hydrazine cross linked iron oxide nanocluster assemblies | Iron Oxide Nanoparticles = 9 nm, Nanocluster = 60 nm | r2/r1 = 4.2 at pH 5.5, r2/r1 = 33.8 at pH 7.4 | pH | T1/T2 switch in contrast capabilities | [25] |
| Fe3O4-ZIF-8 assemblies | Iron Oxide Nanoparticles = 15 nm, Fe3O4-ZIF-8 = 120 nm | r2/r1 = 5.7 at pH 5.0, r2/r1 = 24.6 at pH 7.4 | pH, GSH (redox) | T1/T2 switch in contrast capabilities | [30] |
| i-motif DNA-assisted iron oxide nanocluster assemblies (RIAs) | Iron Oxide Nanoparticles ~3 nm, RIAs = 120 nm | r2/r1 = 7.1 at pH 5.5, r2/r1 = 63.3 at pH 7.4 | pH | T1/T2 switch in contrast capabilities | [31] |
| pH sensitive ‘magnetic nanogrenades’ (PMNs) | Iron Oxide Nanoparticles ~3 nm, PMNs ~60 nm | r2/r1 = 5.8 at pH 5.5, r2/r1 = 13.3 at pH 7.4 | pH | T1/T2 switch in contrast capabilities | [32] |
| Biotin surface modified Gd-doped MSNs | 75 ± 6 nm | Native MSNs r1 = 15.1 mM−1 s−1, Biocapped MSNs r1 = 5.8 mM−1 s−1 | Biotin | Reversible protein recognition | [39] |
| Gd-MSNs-PgPAA | 61 ± 8 nm | r1 = 8.7 mM−1 s−1 at pH 4.0, r1 = 20.1 mM−1 s−1 at pH 7.0 | pH | Fully reversible T1 contrast switch | [40] |
| MnOx integrated hollow MSNs | ~240 nm | r1 = 8.8 mM−1 s−1 at pH 5.0, r1 = 0.8 mM−1 s−1 at pH 7.4 | pH | Multimodal imaging agent (MRI and US) | [41] |
| Fe3O4@C@MnO2 | 130 nm | r2/r1 = 68.7 at pH 5.0, r2/r1 = 201.1 at pH 7.4 | pH | Dual-modal T1/T2 contrast agent | [42] |
| Dopamine-responsive IONPs (DaReNa, SPIO = superparamagnetic iron oxide) | DaReNa = 138 ± 4 nm, 9D7*-SPIO = 52 ± 2 nm, Tyr-PEG-SPIO = 31 ± 1 nm | r2 = 208 ± 2 mM−1 s−1 (DaReNa), r2 = 130–140 mM−1 s−1 individual IONP species | Dopamine | Neurochemistry unaffected | [11] |
| Calcium-responsive nanoparticles (MaCaReNas) | 35 ± 1 nm in absence of Ca2+, 262 ± 14 nm in presence of Ca2+ | r2 = 151 ± 15 mM−1 s−1 with 0 mM Ca2+, r2 = 261 ± 21 mM−1 s−1 with 1.2 mM Ca2+ | Calcium | Allows for calcium activity mapping in the brain | [46] |
| MMP-responsive iron oxide nanoparticles | Azide IONPs = 120 ± 8 nm, Alkyne IONPs = 148 ± 10 nm, presence of MMP enzymes = 780 nm | T2 signal enhancement of ~160% | Matrix metalloproteinase enzymes | Tumour-targeting contrast agent | [52] |
| Manganese oxide nanoparticles | 8 ± 0.7 nm | r2/r1 = 14.1 in absence of superoxide radicals, r2/r1 = 31.7 in the presence of superoxide radicals | Superoxide radicals | Can mimic the enzyme superoxide dismutase, thus catalyse the dismutation of superoxide radicals | [53] |