## 1 Introduction  
Single-molecule enzymology, which focuses on studying single enzyme molecules instead of their large ensembles, is increasing in popularity [1, 2]. This approach utilizes so-called molecular detectors, which allow researchers to investigate enzymes with ultra-high sensitivity [3]: atomic force microscopes [4, 5, 6, 7], nanoelectronic detectors [8, 9, 10, 11], nanopore-based sensors [12, 13], total internal reflection microscopes [2] etc. It should be emphasized that enzymes are now widely employed in analytical chemistry [14, 15, 16]. For example, horseradish peroxidase (HRP) has been employed for the detection of various heavy metal ions using microplate-based colorimetric analysis [14] and conventional spectrophotometry [15]. This enzyme has also been employed for the amperometric detection of phenolic compounds [16]. The importance of the HRP enzyme in analytical chemistry applications determined its use in our present research as a model object. Pyramidal structures are employed in various biosensor devices [17; 18; 19; 20]. [PERSON] et al. [21] performed a theoretical study demonstrating a change in the spatial distribution of an electromagnetic field near pyramidal structures. Moreover, these authors demonstrated that a change in the mutual orientation of a pyramid and in the direction of an incident electromagnetic field lead to a change in the topography of the spatial distribution of electromagnetic fields near the pyramid [21]. In our recent experimental study, a change in the aggregation state of an HRP enzyme upon its adsorption on mica after the incubation of its solution near such a structure was demonstrated using atomic force microscopy (AFM) [22]. One of the advantages of AFM consists in its visualization of the objects under study at the level of individual macromolecules [23]. Furthermore, this is the feature that makes AFM a very useful tool in single-molecule enzymology [3; 4]. Due to its extremely high, single-molecule sensitivity, AFM is capable of revealing even subtle effects of external factors on the structure of biological objects [24], including enzyme macromolecules [25]. As such, by using AFM, it was demonstrated that electromagnetic fields of even a very low power density (of the order of \(10^{-12}\) W/cm\({}^{2}\)) can affect physicochemical properties of enzymes [26]. Regarding the interaction of electromagnetic fields with pyramidal structures, on the one hand, the incubation of HRP solution near a pyramidal structure has been shown to lead to the disaggregation of the enzyme [22]. Such an effect was ascribed to the concentration of an external electromagnetic field in certain points of space at the expense of a resonant interaction of the pyramidal structure with the field [21]. On the other hand, not only normal but also inverted pyramidal structures have been reported to be employed in biosensor devices [17; 20]. Moreover, it should be noted that the effective scattering surface of a pyramidal structure can depend on the angle of incidence of the electromagnetic waves, and, accordingly, the spatial distribution of the electromagnetic fields near this structure can depend on its spatial orientation. In this regard, it is of interest to determine whether the incubation of an enzyme solution in the vicinity of an inverted pyramidal structure has an influence on its properties. Herein, the influence of the incubation of an HRP enzyme solution near an inverted pyramidal structure (ISP) on the enzyme's adsorption properties was studied using AFM, while spectrophotometry was employed as a reference method. We performed these experiments in order to study whether the incubation of the enzyme solution near a pyramidal structure with different spatial orientation influences the enzyme's properties. The incubation of the HRP solution near the ISP's apex and above its base was found to induce an increased aggregation of the enzyme upon its adsorption on mica.