## 6 Methods for Obtaining Selenium-Containing Polysaccharides
### Encapsulation of Nanoselenium Particles into Polysaccharides  
Three methods for preparation of SeNPs are currently used: chemical synthesis [304], physical procedures [346], and biogenic methods utilizing enzymatic reactions in microorganisms, mushrooms, or plants [347]. The polysaccharide-stabilized SeNPs are currently obtained by chemical synthesis and biological and biotechnological methods. Chemical methods using elemental nano-selenium employ the reduction of this element, mostly from the +4-oxidation state, with a reducing agent in the presence of a polysaccharide as a capping agent. Encapsulated nanoparticles form in a colloidal suspension of a characteristic red color. Some selenium precursors are selenious acid, sodium selenite, or sodium hydrogen selenite; reducing agents include ascorbic acid or reducing mono and disaccharides, like glucose and galactose [306; 307; 308; 309; 310; 348; 350; 349; 351; 352]. The process is conducted in the presence of polysaccharides such as chitosan, glucomannan, acacia gum, carboxymethylcellulose, or other polysaccharides with different molecular properties and chain conformations [302; 353]. The polysaccharides are used as stabilizers and coating agents to obtain stable and water-dispersible selenium nanoparticles. The procedure to obtain encapsulated SeNPs is simple and includes several steps [354]: (1) adding a vitamin C solution to an aqueous solution of polysaccharides, and mixing uniformly; (2) adding dropwise, with mixing, a selenium dioxide solution or a selenite solution; (3) adding water to the solution to obtain a polysaccharide functionalized nano-selenium hydrosol. The product is stored in the form of sol in an aqueous solution. Chemical methods of SeNPs preparation are more effective than biological and biotechnological methods; however, the risk of presence of toxic by-products unacceptable in medicinal preparations and dietary supplements led to the development of novel biogenic methods, typical of green chemistry. In green synthesis, a bioreductive capacity of plant extracts is utilized for preparation of selenium nanoparticles. The components of the complex plant extracts (among others polysaccharides) may act as good encapsulating stabilizing agents and facilitate the formation of stable colloidal nanoparticles [355]. Several plant extracts were used for the synthesis and stabilization of the SeNPs, e.g., tea extract [45], aqueous extract of _Allinum sativum_[356], leaf extract of _Clausen dentata_[357], polysaccharide solutions extracted from _Undaria pimattifala_[358], and leaf extract of _Terminalia arjuna_[359]. Biosynthesis of encapsulated SeNPs using plant extracts is inexpensive and does not require any special conditions [304]. Several organisms such as plants, fungi, or bacteria have the ability to convert some toxic ions to less toxic forms including metal precipitants or formation of NPs [360; 361]. This capacity is based on the involvement of oxidoreductase in the detoxification process, in case of an excess of harmful factors in the environment. The ability to reduce excess amounts of selenium in the oxidation state +6 or +4 to elemental selenium, often to red selenium in the form of nanoparticles, has been observed in many organisms. Due to that  
Figure 11: The proposed linear (**a**) and cyclic (**b**) structures of selenodextrin (according to [PERSON] et al. [345]). ability, the cultures of microorganisms or mushroom may be used for synthesizing SeNPs with an ecofriendly approach [362; 363; 364; 365]. Several types of bacteria and cyanobacteria cultivated in submerged cultures have already been used for the biosynthesis of SeNPs, and these include _Escherichia coli_[366], _Enterobacter cloacea_[367], _Pseudomonas aeruginosa_[368], _Klebsiella pneumoniae_[369], _Zooglea ramifera_[370], _Lactobacillus casei_[371], _Streptomyces_ sp. [372], _Arthrospira [Spirulina] platensis_[373], and many others. Further, fungal cultures may be used for in vivo synthesis of SeNPs.