Selenium is one of the essential trace elements in organisms and has many physiological functions. Adding proper amount of selenium to the feed can improve the antioxidant capacity and immune function of the animal, maintain the health of the body, and promote the growth and development of the animal. Nano-selenium is a nano-particle with protein as core, elemental selenium as membrane and protein as dispersing agent. The color of nano-selenium particles has been reported to be mainly red and taupe, and red nano-selenium has high biological activity. This paper introduces the preparation methods of nano-selenium and its application in livestock breeding in recent years. The
Bioactivity, toxicological properties and preparation methods of 1 nm selenium
1.1 Biological Activity
Selenium has biological activities such as anti-cancer, anti-virus, anti-oxidation and immune regulation. Selenium has important biological effects in the body: participates in the synthesis of glutathione peroxidase (GSH-Px), protects cell membrane structure and function; It stimulates the production of immunoglobulins and antibodies, antagonizes and reduces the toxicity of certain toxic elements and substances; participates in the tricarboxylic acid cycle, regulates thyroid hormones through type I 5-deiodinase to affect the body's metabolism, affecting vision transmission and fertility. Numerous studies have shown that nano-selenium, like inorganic selenium and organic selenium, has high biological activity, but it has different characteristics from both, showing low toxicity and high efficiency. In terms of biological efficacy, nano-selenium scavenges hydroxyl radicals in vitro. The efficiency is 5 times that of inorganic selenium and 2.5 times that of organic selenium. Also. Nano-selenium showed a health-care effect such as inhibition of tumor and immune regulation at a very low dose, and the corresponding low-dose inorganic selenium did not have this effect. Nano-selenium has the effects of enhancing immunity, inhibiting tumor, anti-aging and anti-oxidation in mice. At present, the research on the biological activity of nano-selenium is relatively superficial, and its activity needs to be compared with other active forms, and its mechanism of action needs further exploration.
1.2 Toxicological properties
In terms of acute toxicity, inorganic selenium is 15 mg/kg body weight, organic selenium is 30-40 mg/kg body weight, and nanoselenium is 113 mg/kg body weight. The study found that the acute toxicity of nano-selenium is about 1/7 of that of sodium selenite. The glutathione response capacity is about 1/10-1/20 of sodium selenite. In terms of short-term toxicity, selenite is more likely to cause significant oxidative stress, liver damage, and growth retardation than nano-selenium. In terms of subchronic toxicity, the content of inorganic selenium or organic selenium in the feed at 4-5 mg/kg body weight can cause weight loss and cirrhosis in rats, while nano-selenium does not occur at 6 mg/kg body weight. The negative effects of nano-selenium on growth retardation, hematological parameters, serum pathological markers and protein parameters, related organ weight and liver damage were significantly better than selenite and high-selenium protein in known selenium preparations. The highest security.
1.3 Preparation method
Because nano-selenium has great application prospects in animal nutrition, materials, medicine and other fields, its synthesis and research have attracted wide interest from scholars at home and abroad. At present, relevant researches mainly focus on the preparation technology and morphology of nano-selenium. The prepared preparation methods include solid phase surfactant method, microemulsion method, protein template method, polymer template method, ultrasonic chemistry method, temperature control method and Electrochemical method, etc.
The template method synthesis of nano-selenium has the advantages of small particle size, good dispersion, stable, good morphology, low pollution, low energy consumption, etc., but the reaction steps are more and the time is longer. Wang Hongyan et al. used natural polymer chitosan as soft template aqueous phase to prepare nano-selenium, and obtained uniform and stable spherical nano-selenium particles with an average particle size of about 50 nm. Zhang et al. used chitosan as a soft template to synthesize nano-selenium particles with uniform distribution and particle size of about 10 nm, which has good adhesion and biological activity. The hydrothermal synthesis method has low synthesis temperature, mild conditions, stable system, high purity, good dispersibility and narrow particle size distribution, but the reaction equipment has high requirements, which is not conducive to industrial production. An et al. used selenite and thiosulfate as raw materials, and prepared three-square nano-selenium with a particle size of 10-60 nm by hydrothermal method using different reducing agents. Wang et al. used sodium selenosulfate as raw material to prepare nano-selenium rods with a particle size of about 50 nm by hydrothermal method under the action of polyvinyl alcohol. Chen et al. ultrasonically mixed ethylenediamine, selenium powder and water to prepare nano-selenium rods with a particle size of about 50 nm. Solid-state reaction at room temperature is a new research field developed in recent years. Because it is a solvent-free reaction, it can simplify the reaction process, reduce side reactions and interference factors, improve reaction yield and purity, and thus has easy operation and control, high selectivity, and pollution. With less characteristics and energy saving, it has good application and development prospects in industrial production. Wang Runxia et al used sodium sulfite and ascorbic acid as reducing agents to reduce selenium dioxide and solid phase reaction at room temperature to prepare nano-selenium with various morphologies.
There are also reports on other preparation methods. Zhang Xu et al. prepared single crystal nanowires having a diameter of 50 nm and a length of 5 μm in a buffer system formed of polyacrylic acid and a sodium salt thereof at room temperature. Zhu et al. heated the mixture of selenium dioxide and ethylene glycol to 195 ° C in a microwave at a constant temperature for 30 min to obtain nano-selenium having a particle size of about 60 nm. Jiang et al. induced the growth of nano-selenium with nano-silver particles to obtain nano-selenium with a particle size of about 23 nm.
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