## 3 Results  
### Results of AFM Sensor Measurements  
Figure 2 displays typical AFM images of the mica surface with HRP biomolecules adsorbed from the working solutions and from the control solution, and corresponding cross-section profiles indicated by the lines in the images. Figure 3 displays the density functions of distribution of the imaged objects with height \(\rho\)(_h_), plotted based on the AFM data summarized for each sample.  
As seen from Figure 2a, in the control experiment, when the cell containing HRP solution was placed far away from the polymeric pipe coil, the protein adsorbs onto the mica surface in the form  
Figure 3: Results of processing of data obtained upon the AFM analysis of HRP solutions. Typical plots of distribution of the imaged objects with height \(\rho(t)\). The cell with HRP solution was placed either far away at a 10-m distance from the polymeric pipe coil (control experiment, black line) or over the coil (red line).  
Figure 2: Results of atomic force microscopy (AFM) analysis for horseradish peroxidase (HRP) solutions: typical AFM images of the mica surface with adsorbed HRP particles (left) and corresponding cross-section profiles indicated by lines in the AFM images (right). The measuring cell (containing HRP solution) was placed either far away at a 10-m distance from the polymeric pipe coil (control experiment) (**a**) or over the coil (**b**).  
of compact objects with heights from 1.0 to 4.0 nm. The \(\rho\)(_h_) plot (Figure 3, black line) indicates that the maximum number of molecules have a height of 1.6 \(\pm\) 0.2 nm. The molecular weight of HRP is known to be 40 to 44 kDa [21; 22]. Furthermore, other proteins with similar \(M_{r}\) were reported to have comparable sizes: putidaardoxin reductase, \(h_{max}\) = 1.8 nm [27], \(M_{r}\) = 45.6 kDa [35]; adrenodoxin reductase, \(h_{max}\) = 1.8 nm [36], \(M_{r}\) = 54 kDa [37]. Our data obtained herein are also in coincidence with the results obtained in our previous studies by AFM [26; 28]. For these considerations, one can conclude that the objects with \(\sim\)1.6-nm height, observed upon AFM scanning, can be attributed to HRP monomers.  
At the same time, the \(\rho\)(_h_) plot for the control sample has an inflection point near 2.2 nm, which indicates a non-monotonic dip of the \(\rho\)(_h_) curve near this point. The latter indicates that there is an additional contribution from objects with high heights (i.e., aggregates of biomolecules) to the right wing of the distribution in the region of heights above 2.2 nm. That is, it has been observed that HRP biomolecules, adsorbed from the control solution, present on the AFM chip in the form of a mixture of monomers and aggregates.  
Figure 2b displays typical AFM images of the mica surface with HRP biomolecules adsorbed from the solution placed in the cell over the coil (see Figure 1). As seen from Figure 2b, objects with heights from 1 to 5 nm are visualized. The analysis of \(\rho\)(_h_) function obtained for this sample (Figure 3, red line) indicated that the distribution maximum is 1.4 \(\pm\) 0.2 nm, what coincides with analogous values obtained for the other sample. However, a significant increase in the contribution to the right wing of the distribution--that is, an increased number of objects with heights from 2.2 to 4.2 nm--is observed. The appearance of objects with heights in the range from 2 to 4 nm on the mica surface after its incubation in the analyzed sample indicates an increase in the protein aggregation rate in the analyzed solution.