Used as a photoinitiator for polymerization of polyacrylamide gels. It forms free radicals in aqueous solution in the presence of light. Riboflavin photodecomposes to leucoflavin. No free radicals are formed in the absence of oxygen but traces of oxygen allows for leucoflavin to reoxidize with free-radical generation. The catalysts TEMED or DMAPN are commonly added to speed up the free radical formation. The free radicals will cause acrylamide and bis-acrylamide to polymerize to form a gel matrix which can be used for electrophoresis. Riboflavin is commonly used in the stacking gel for non-denaturing polyacrylamide electrophoresis because native proteins can be senstive to persulfate ions from ammonium persulfate. Another advantage of riboflavin over ammonium persulfate is that it will not start polymerization until the gel is illuminated.