Why can't I get silver nanoparticles by the Spirulina platensis biosynthesis?

I use the 1 ml of water extract of dried Spirulina (1gm/5ml),added to 25 ml of 1 mM AgNO3 then left in light shaking to get a purple solution instead of the brown one of the AgNPs.

08 November 2016 258 8 View