## 4 Materials and Methods
### Preparation and Characterization of Selenium Nanorods  
Selenium nanorods were obtained by laser ablation of solid target and subsequent laser fragmentation of obtained Se nanoparticles in propanol-2. Resulting Se nanorods were transferred to deionized water with a resistivity of 20 M\(\Omega\)cm. At the first stage, a solid target of Se was placed at the bottom of the cuvette under a thin layer of chemically pure propanol-2 (layer thickness was no more than 2-3 mm). The target was irradiated with a laser beam through a thin layer of propanol-2 (\(\lambda\) = 1064 nm; T = 4 ns; f = 1 kHz; P = 20 W; Ep = 2 mJ). The beam was moved on the target surface along a given trajectory in the form of parallel straight lines inscribed in a rectangle using an LSCanH galvanomechanical scanner (Ateko-TM, Moscow, Russia) and F-Theta lens. The typical time of ablation was 30 min.  
At the second stage, the colloid of Se nanoparticles in propanol-2, which was obtained as a result of ablation, was additionally irradiated with same laser parameters in the absence of solid target during 1 h.  
At the final stage, Se nanoparticles were transferred in deionized water by centrifugation and washing in various chemical solvents. The washing process is necessary to purify the solution from the decomposition products of propanol-2 molecules forming as a result of optical breakdown.  
Initially, SeNrs nanoparticles were precipitated using an LMC-4200 centrifuge (Biosan, Riga, Latvia). Centrifugation took place at 4200 rpm for 15 min. Propanol-2 was taken from the solution with precipitated nanoparticles, and a chemically pure solution of carbon tetrachloride (CCI4) was poured instead of propanol-2. The resulting solution was placed in an ultrasonic bath (ultrasonic power was 20 W) for 10 min. Similar procedures for centrifugation, replacement of the solution, and the use of ultrasound were carried out for dimethyl sulfoxide (C\({}_{2}\)H\({}_{6}\)OS), chloroform (CHCl\({}_{3}\)), and acetone (C\({}_{3}\)H\({}_{6}\)O). At the last stage, solvent was replaced by MQ-water.  
The morphology of nanoparticles was studied by a 200 FE transmission electron microscope (Carl Zeiss Microscopy GmbH, Jena, Germany). According to transmission electron microscopy data, obtained Se nanoparticles have a form of nanorods (Figure 9A,B). The size of nanoparticles was characterized using a DC24000 analytical centrifuge (CPS Instruments, Prairieville, LA, USA). Nanoparticle concentration and hydrodynamic radius were evaluated using Zetasizer Ultra Red Label (Malvern, UK). It was found that the selenium nanoparticles have a bimodal size distribution (Figure 9C). The first peak of particle distribution was located at 120 nm, the half-width was in the range of 90-160 nm, the second peak of the distribution was located at 900 nm, the half-width was in the range of 600-1300 nm. The volume-size distribution of the obtained nanoparticles showed that the bulk of the volume of the nanoparticles was concentrated around the size of 1000 nm (Figure 9D).  
Figure 9: Shape and size distribution of Se nanorods. (**A**) TEM image of obtained Se nanoparticles (dark field image). (**B**) TEM image of an individual nanoparticle with a diameter of 70 nm and length of 1 \(\upmu\)m (dark field image). (**C**) Size distribution of selenium nanoparticles. (**D**) Volume distribution of selenium nanoparticles. Data obtained using an analytical disk centrifuge and confirmed by DLS. PDI = 0.28 \(\pm\) 0.5; (n = 3).