## 3 Results  
### Particle Size, Colloidal Stability, and Crystal Structure  
The colloidally stable FA-PAA-coated MnO nanoparticles were prepared via a simple one-pot polyol method (last step in Figure 1). The nanoparticle diameter (d) was measured via HRTEM. The nanoparticles were ultrasmall (Figure 2a-i), and a magnified image of a nanoparticle, indicated as a dotted circle in Figure 2a-i, showed the MnO nanoparticle lattice fringes (Figure 2a-ii). The estimated average particle diameter was 2.7 \(\pm\) 0.1 nm from a log-normal function fit to the observed particle diameter distribution (Figure 2b and Table 1). The hydrodynamic diameter (a) of the FA-PAA-coated MnO nanoparticles was measured via DLS, and the estimated average hydrodynamic diameter was 22.2 \(\pm\) 0.1 nm from a log-normal function fit to the observed hydrodynamic diameter distribution (Figure 2c and Table 1).  
The nanoparticle colloidal stability was confirmed by visually inspecting the aqueous nanoparticle suspension sample (36.4 mM Mn) (Figure 3a-i): since preparation, no nanoparticle precipitation occurred (>1 year). Further, no nanoparticle precipitation occurred for the dilute aqueous nanoparticle suspension samples (2.0 mM Mn) in the presence of 1.0 mM Ca\({}^{2+}\) and Mg\({}^{2+}\) ions for 5 days (Figure 3a-ii,a-iii, respectively, indicating no effects of these biologically important ions on the nanoparticle colloidal stability). Additionally, the high zeta potential (\(\upxi\)) of -32.6 \(\pm\) 0.4 mV (Figure 3b and Table 1) further confirmed the colloidal stability. Colloidal dispersion was confirmed through the Tyndall effect: laser light scattering was only observed in the nanoparticle suspension sample, caused by the  
\begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multicolumn{2}{c}{**Particle Dimension**} & \multicolumn{3}{c}{**Surface-Coating**} & \multirow{3}{*}{**Magnetic Properties**} & \multicolumn{3}{c}{**Water Proton Spin**} \\  & \multicolumn{3}{c}{**(nm)**} & & \multicolumn{3}{c}{**Amount**} & & \multicolumn{3}{c}{**(s\({}^{-1}\)mM\({}^{-1}\))**} \\ \hline \multirow{2}{*}{d\({}_{\text{avg}}\)1 [FOOTNOTE:1]Footnote 1: d\({}_{\text{avg}}\): Average particle diameter. 2 \({}_{\text{avg}}\): Average hydrodynamic diameter. 3 \({}_{\text{avg}}\): Average zeta potential. 4 \({}^{\text{P}}\): Average surface-coating amount per nanoparticle in wt%. 5 \({}^{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{ \text{\text{\text{\text{\text{\text  
collision between the nanoparticle colloids and the passing laser light. Contrastingly, it was not observed in the reference triple-distilled water (Figure 3c).  
As shown in Figure 4, the XRD pattern obtained before TGA show significantly broad peaks (bottom spectrum), probably since most of the nanoparticles were not fully crystallized owing to their ultrasmall particle sizes. However, after TGA, sharp peaks were observed (top spectrum), due to the particle growth and crystallization of the nanoparticles. All post-TGA peaks could be assigned with (hkl) Miller indices. They corresponded to the cubic structure of MnO with characteristic peaks of (111), (200), (220), (311), (222), and (400) as indicated on the top of the XRD pattern. The estimated cell constant (L) of 4.43 \(\pm\) 0.1 A was consistent with the reported value [30].