## 3 Results
### Physicochemical Analyses
The experimental scattering profiles from the  
Figure 10: The N 1s photoelectron spectra of samples MTX (**a**) and AuFe-MTX (**b**). Figure 9: The C 1s photoelectron spectra of samples MTX (1), AuFe (2) and AuFe-MTX (3), normalized by the intensity of the main peak. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{**Group**} & \multicolumn{2}{c}{**C(O)-N-C(O),**} & \multirow{2}{*}{**N (MTX), NR3**} & \multirow{2}{*}{**N–E**} \\  & & **NH3+** & & \\ \hline \multirow{3}{*}{MTX} & E\({}_{\text{b}}\), eV & 401.0 & 399.9 & 398.8 \\  & W, eV & 1.15 & 1.15 & 1.15 \\  & I\({}_{\text{rel}}\) & 0.08 & 0.86 & 0.05 \\ \hline \multirow{3}{*}{AuFe-MTX} & E\({}_{\text{b}}\), eV & 400.9 & 399.9 & 398.7 \\  & W, eV & 1.15 & 1.15 & 1.15 \\  & I\({}_{\text{rel}}\) & 0.06 & 0.77 & 0.17 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Characteristics of photoelectron spectra N 1s (E\({}_{\text{b}}\)—binding energy; W—peak width; I\({}_{\text{rel}}\)—relative intensity). bimetallic nanoparticles, their conjugates with MTX and their distribution functions DV(R) of the scattering particles (obtained with volume dimensions in the acetone medium) are presented in Figure 11.  
The analysis of the experimental SAXS curves showed that they correspond to poly-disperse systems. The initial sections of the SAXS patterns show an upward trend, which indicates the presence of large aggregates in the samples. In the experimental curves, there is practically no scattering from the spherical shape of nanoparticles (form factor). However, the SAXS curves from AuFe show a weak presence of a form factor, possibly from individual particles and/or their small aggregates, in contrast to the curve describing AuFe-MTX (Figure 11a, curve 2). The distribution functions DV(R) calculated with the method from [38] are shown in Figure 11b. The functions are bimodal. It was found that the bimetallic samples are characterized by the presence of highly homogeneous populations of individual NPs along with a wide fraction of large aggregates. Fe metal particles contain both small particles with an average radius of about 4.6 nm and aggregates with radii up to 45 nm. In the presence of MTX, the number of aggregates increases, and the proportion of small conjugate nanoparticles becomes more pronounced. Apparently, the introduction of MTX leads to an increased interaction between the nanoparticles and, as a consequence, to the formation of a larger number of large aggregates in conjugates. Additional information about the electronic state and local environment of gold and iron atoms in composites was obtained using XANES (X-ray absorption near the edge of the structure) and EXAFS (extended X-ray absorption of a fine structure), absorption at the K-edge of iron absorption and at the L3-edge of gold absorption (see Supplementary Materials, Methods). Comprehensive studies have shown that the environment of iron atoms is similar to the structure of Fe\({}_{3}\)O\({}_{4}\), and the spectra of gold in the sample did not show a significant difference from metallic gold. The Fourier transformant of the Au spectrum detected a complex structure with additional maxima at short distances, but EXAFS did not confirm the formation of AuFe alloy particles. The powder diffraction pattern of the AuFe sample indicates an amorphous structure with Bragg peaks being consistent with bulk gold and, possibly, magnetite. Figure 11: Small-angle X-ray scattering (SAXS) patterns from the AuFe nanoparticles obtained in acetone medium along with those from their conjugates AuFe-MVX: (**a**) experimental SAXS curves from AuFe (1) and AuFe-MTX (2). Panel of (**b**) the volume size distribution functions DV(R) calculated from AuFe (1) and AuFe-MTX (2).