In previous experiments I've used two complex compounds - Potassium hexacyanoferrate(II) and Potassium hexacyanoferrate(III). First has a yellowish color and the second one is bright red. When you make aqueous solutions of these salts one of it is nearly colorless (just slightly yellow (can't see in the picture)) and the other one is yellow (when concentration is higher the solution becomes yellow - green).
Potassium hexacyanoferrate(III) solution can show some fluorescence, that means it can emit light when it's illuminated by light which has higher energy. I'm going to show it in the future posts.
These compounds are nontoxic in the body, because does not release free cyanide ions which even in low concentrations are highly toxic (deadly). Potassium hexacyanoferrate(III) is used in many amperometric biosensors as an electron transfer agent replacing an enzyme's natural electron transfer agent such as oxygen.
