## 3 Results and Discussion
### Study of the Physicochemical Properties of Aqueous IgG Colloid of Different Concentrations
This explains why no pronounced scattering is observed in the absorption spectrum in the long-wave region of the visible range. The shape of the size distribution changes when the aqueous protein colloid is exposed to an alternating magnetic field (8 Hz). The average size increases to 18 nm, and a significant broadening of the peak is observed. This broadening is probably explained by the fact that the \(\sim\)3% of protein molecules is located in aggregates. This is due to the fact that the \(\sim\)3% of protein molecules are located in aggregates. This is due to the fact that the \(\sim\)3% of protein molecules are located in aggregates. the presence in the colloid of significant quantities of not only individual protein molecules, but also dimers, trimers, and larger aggregates. Aggregates with an average size of about 400 nm, consisting of approximately 5 \(\times\) 10\({}^{4}\) protein molecules, have also been recorded. There are about 10\({}^{5}\)-10\({}^{6}\) individual molecules per aggregate in the colloid. The shape of the size distribution changes less significantly when the aqueous protein colloid is exposed to an alternating magnetic field (50 Hz). The average size does not change, although a significant broadening of the peak is observed. Aggregates with an average size of about 200 nm, consisting of approximately 6 \(\times\) 10\({}^{3}\) protein molecules, have also been recorded. There are more than 106 individual molecules per aggregate in a colloid. When an aqueous protein colloid is exposed to mechanical mixing at frequencies of 4.4 and 12 Hz, the size distribution does not change significantly. The average size does not change, although some broadening of the peak is observed. A significant change in the size distribution can be considered in the absence of a significant number of aggregates in the diameter range 50-1000 nm. In other words, mechanical stirring can lead to disaggregation of protein aggregates with a hydrodynamic diameter of 30-50 nm. Obviously, the destruction of protein aggregates should lead to increasing viscosity of the aqueous colloid [57]. The impact of an alternating magnetic field with frequencies of 8 and 50 Hz, as well as mechanical stirring with frequencies of 4.4 and 12 Hz, on the change in the dynamic viscosity of IgG colloids is 0.01-1 mg/mL at a shear stress of 100 s\({}^{-1}\) (Figure 5c). These shear stresses were chosen because they showed the greatest differences between groups of colloids with different protein concentrations. It was shown that statistical differences under the influence of physical factors were recorded only at protein concentrations of 0.1-1 mg/mL and only under mechanical influence. It should be noted that the differences in dynamic viscosity did not exceed 20%. In this case, magnetic fields did not affect the viscosity of protein colloids. It is probably these qualities of protein colloids that make it possible to use Brownian relaxation for immunoassays [58]. Today, magnetization harmonics, induced with a small low-frequency oscillating magnetic field, are actively used to obtain quantitative information about the microenvironment of magnetic nanoparticles coated with antibodies [59]. Using differential ultrasonic spectroscopy, the impact of a magnetic field with frequencies of 8 and 50 Hz, as well as mechanical stirring with frequencies of 4.4 and 12 Hz, was studied on the properties of an aqueous colloid of IgG antibodies with concentrations from 0.01 to 1 mg/mL (Figure 5d). It has been established that the studied effects do not lead to essential variation in the ratio of resonant frequencies in the measuring cell and the comparison cell. It was shown that statistical differences under the influence of physical factors were recorded only at protein concentrations of 1 mg/mL and only under mechanical influence. It should be noted that the differences in the frequency ratio characterizing the speed of sound in the colloid did not exceed 0.3%.