## 2 Materials and Methods  
### Synthesis and Morphology of Selenium Nanorods  
To obtain SeNrs, the technique of laser ablation of a bulk selenium followed by laser fragmentation of a colloid of SeNPs in propanol-2 was used. Then the colloidal liquid with selenium nanorods was replaced with highly purified water with a resistivity of 18.6 M\(\Omega\)cm. The laser ablation procedure for obtaining spherical selenium particles took place in several stages. Initially, a polished selenium target was attached to the bottom of the glass cuvette, then chemically pure isopropanol was poured into the cuvette. The volume of the liquid was chosen so that the thickness of the fluid between the liquid surface and the target was approximately 2-3 mm. Then the laser source with the following parameters \(\lambda=1064\) nm, \(f=1\) kHz, \(\tau=4\) ns, Ep \(=2\) mJ irradiated the selenium target. During irradiation, the beam moved along the surface of the Se target using a galvanomechanical scanner LScanH (Ateko-TM, Moscow, Russia) and an F-Theta lens. The trajectory of the beam consisted of several parallel lines written in a square. The typical ablation time was 30 min. The second stage of colloidal irradiation was carried out without the use of a selenium target. Selenium nanoparticles obtained as a result of ablation in propanol-2 were repeatedly irradiated with laser radiation with the same parameters for an hour. The liquid in the colloid of selenium nanoparticles was replaced by deionized water after several stages of particle settling in a centrifuge and solvent replacement. The transfer of selenium nanoparticles from propanol-2 to deionized water took place in several stages. Selenium nanorods were initially precipitated by centrifuge LMC-4200 (Biosan, Riga, Latvia). The sedimentation of nanoparticles in the centrifuge was carried out for 15 min at a speed of 4200 rpm, rotor radius 0.12 m, Relative Centrifugal Force \(\sim\)2400 g. After centrifugation of the solution, propanol-2 was replaced with a carbon tetrachloride (CC14). Then the colloid was exposed to ultrasound inside an ultrasonic bath (P = 20 W) for 10 min. Next, the colloid liquid was replaced sequentially with dimethyl sulfoxide (C\({}_{2}\)H\({}_{6}\)O\({}_{5}\)), chloroform (CHCl\({}_{3}\)) and acetone (C\({}_{3}\)H\({}_{6}\)O) using the described centrifugation and ultrasonic treatment procedures at each step. After another colloid centrifugation procedure, acetone was replaced by deionized water. A possible mechanism for the formation of selenium nanorods during fragmentation is shown in Figure 1A. As a result of the ablation of a solid target of selenium nanoparticles, large nanoparticles (100-200 nm) are present in the colloid. As a result of laser fragmentation, the size of nanoparticles decreases; along with this, the concentration of nanoparticles increases. In turn, an increasing concentration of nanoparticles in a colloid can lead to an increase in the rate of aggregation processes, leading to the formation of elongated nanorods of nanoparticles. As a result of laser heating and redistribution of the surface energy, the nanoparticles melt with each other, forming nanorods. A Libra 200 FE HR transmission electron microscope (Carl Zeiss, Jena, Germany) was used to obtain TEM images of the particles and study its morphology. Microscopic  
Figure 1: SeNrs formation scheme, shape and distribution by size. (**A**) Schematic diagram of a possible synthesis mechanism for SeNrs during laser fragmentation. (**B**) TEM image of a single selenium rod (scale mark size: 200 nm). (**C**) TEM image of obtained Se nanorods (scale mark size: 1 \(\upmu\)m). (**D**) SeNrs number distribution by size. (**E**) SeNrs volume distribution by size. Disc centrifuge and a DLS particle size analyzer were used to collect data. PDI = 0.25 \(\pm\) 0.5; (\(n\) = 3). grids made of Au were used during SeNPs preparation for TEM microscopy. It follows from the transmission microscope images that selenium nanoparticles have the shape of nanorods (Figure 1B,C).