Agar (Noble) BD Difco™ 500 g. Noble Agar is extensively washed and bleached. This agar should be used for immunodiffusion, some electrophoretic applications, and as a substrate for mammalian and plant tissue culture. Agar Noble is a solidifying agent that is essentially free of impurities. It is used in electrophoretic and nutritional procedures and in preparing microbiological culture media when increased purity is required.