Poly-L-Lysine with a molecular weight greater than 150,000 (150,000-300,000) should be used. To make a stock solution: Take 0.1% Poly-L-Lysine in distilled water and store it in a dispensing vial and freeze it at -20°C. A drop (10-15ml) is dispersed at the end of a clean glass slide and smeared along its length with the end of another clean glass slide in the same way as blood film. Make sure that the film of Poly-L-Lysine is thin enough for interference colors to be seen as it is being smeared. The slide is ready to use within minutes of drying.
If the Poly-L-Lysine is properly applied , it will not affect immunostaining, but it may cause precipitation in some silver impregnation methods. Therefore, It should be avoided if immunogold-silver methods are to be used.