EPR and Structural Characterization of Water-Soluble
Mn<sup>2+</sup>-Doped Si Nanoparticles
- Publication date
- Publisher
Abstract
Water-soluble
poly(allylamine) Mn<sup>2+</sup>-doped Si (Si<sub>Mn</sub>) nanoparticles
(NPs) were prepared and show promise for
biologically related applications. The nanoparticles show both strong
photoluminescence and good magnetic resonance contrast imaging. The
morphology and average diameter were obtained through transmission
electron microscopy (TEM) and high-resolution transmission electron
microscopy (HRTEM); spherical crystalline Si NPs with an average diameter
of 4.2 ± 0.7 nm were observed. The doping maximum obtained through
this process was an average concentration of 0.4 ± 0.3% Mn per
mole of Si. The water-soluble Si<sub>Mn</sub> NPs showed a strong
photoluminescence with a quantum yield up to 13%. The Si<sub>Mn</sub> NPs had significant <i>T</i><sub>1</sub> contrast with
an <i>r</i><sub>1</sub> relaxivity of 11.1 ± 1.5 mM<sup>–1</sup> s<sup>–1</sup> and <i>r</i><sub>2</sub> relaxivity of 32.7 ± 4.7 mM<sup>–1</sup> s<sup>–1</sup> where the concentration is in mM of Mn<sup>2+</sup>. Dextran-coated poly(allylamine) Si<sub>Mn</sub> NPs produced NPs
with <i>T</i><sub>1</sub> and <i>T</i><sub>2</sub> contrast with a <i>r</i><sub>1</sub> relaxivity of 27.1
± 2.8 mM<sup>–1</sup> s<sup>–1</sup> and <i>r</i><sub>2</sub> relaxivity of 1078.5 ± 1.9 mM<sup>–1</sup> s<sup>–1</sup>. X-band electron paramagnetic resonance spectra
are fit with a two-site model demonstrating that there are two types
of Mn<sup>2+</sup> in these NP’s. The fits yield hyperfine
splittings (<i>A</i>) of 265 and 238 MHz with significant
zero field splitting (<i>D</i> and <i>E</i> terms).
This is consistent with Mn in sites of symmetry lower than tetrahedral
due to the small size of the NP’s