text: In summary, we have presented a general model of nanos- 
  tructured chemical sensors which takes the adsorption en- 
  ergies of the relevant chemical species and their individual 
  scattering resistances as the only input. On the basis of this 
  model we have performed a computational screening of tran- 
  sition metal doped CNTs, and found that Ni-doped CNTs are 
  promising candidates for detecting CO in a background of air. 
  The model may be applied straightforwardly to other nanos- 
  tructures than CNTs, other functionalizations than metal dop- 
  ing and other gas compositions than air. 
  
  [14] S. B. Fagan, R. Mota, A. J. R. da Silva, and A. Fazzio, “Ab 
  initio study of an iron atom interacting with single-wall car- 
  bon nanotubes”, Phys. Rev. B 67(20), 205414 (May 2003), 
  doi:10.1103/PhysRevB.67.205414. 
  
  [15] Y. Yagi, T. M. Briere, M. H. F. Sluiter, V. Kumar, A. A. Farajian, 
  and Y. Kawazoe, “Stable geometries and magnetic properties of 
  single-walled carbon nanotubes doped with 3d transition met- 
  als: A ﬁrst-principles study”, Phys. Rev. B 69(7), 075414 (Feb 
  2004), doi:10.1103/PhysRevB.69.075414. 