Isotopic Dependence of the Casimir Force
  We calculate the dependence of the Casimir force on the isotopic composition of the interacting objects. This dependence arises from the subtle influence of the nuclear masses on the electronic properties of the bodies. We discuss the relevance of these results to current experiments utilizing the iso-electronic effect to search at very short separations for new weak forces suggested by various unification theories. 
Dennis E. Krause and Ephraim Fischbach