Method of making colloidal selenium nanoparticles

A method of making colloidal selenium nanoparticles, comprising steps of:

• Step (A):
• providing a reducing agent and an aqueous solution containing a selenium precursor;
• Step (B):
• mixing the aqueous solution containing the selenium precursor and the reducing agent in a reaction vessel to form a mixture solution and heating the mixture solution to undergo a reduction reaction and produce a composition containing selenium nanoparticles, residues and a gas in the reaction vessel, and guiding the gas out of the reaction vessel during the heating;
• wherein the heating continues until an amount of the residues is less than 20% by volume of the mixture solution;
• wherein a heating temperature in Step (B) ranges from 50° C. to 200° C.;
• and
• Step (C):
• dispersing the selenium nanoparticles with a medium to obtain the colloidal selenium nanoparticles at a dispersion temperature ranging from 20° C. to 80° C.;
• wherein the reducing agent comprises a first reducing agent or a second reducing agent;
• wherein the first reducing agent is selected from the group consisting of:
• citric acid, lactic acid, glycolic acid, ascorbic acid, oxalic acid, tartaric acid, 1,4-butanediol, glycerol, acetaldehyde, monosaccharide, disaccharide and any combination thereof;
• and
• the second reducing agent is selected from the group consisting of:
• poly(ethylene glycol), polyvinylpyrrolidone, polysaccharide and any combination thereof.