If you need to clear the leaf, try house bleach, or a mixture of KOH and SDS.

You have to test the concentrations and the times by yourself, depending on the nature of your samples!

Hydrogen peroxide together with UV . Sometimes the leaf is so thick and succulent that resists everything. High concentration of Polyphenols can make the thing worse …

Thank you so much Mario, I have used bleaching method and koh but SDS! is that method for  breaking  the protein structure?

Thank you Sergio but  my specimen is thin not succulent.

Try nitric acid and controlated head 60ºC, Time depends on the sample.   

try Dimethylsulfoxide. That at least extract all the chlorophyll and bleach the leaf.

thank you so much Maria and Bingru. I will do these methods.