Comment on "Optimal Reaction Time for Surface-Mediated Diffusion"
  In recent letter [Phys. Rev. Lett {\bf 105}, 150606 (2010)], the surface-mediated diffusion problem is theoretically discussed, and interesting results have been obtained. However, for more general cases, the ansatz of solutions of the diffusion equation, which is the starting point of their analysis, might not be appropriate. In this comment, suggested ansatz and corresponding methods will be presented. 
Yunxin Zhang
math-ph math.MP