Subject: Can we be 100% sure that DNA is the transforming principle

im aware of the transforming principle experiment done by  Frederick Griffith, 
Avery , McLeod and McCarty and the Hershey and Chase experiment. All these 
experiments point to DNA as the molecule that carries genetic information , 
but there is still the possibility of contaminations of proteins and /or RNA 
since DNA came originally from a biological source (cells)

Can a experiment be designed that it will 100% prove the case? or what can be 
done to ensure that the possibility is close to a 100% .

Re: Can we be 100% sure that DNA is the transforming principle