There is something wrong with this text (taken from an article) The advantage of this approach is the label-free methodology over the use of dyes. Geng et al.30 investigated the interaction between hydrogen sulfide gas molecules and gold nanoparticles. In each sensing cell, chromium electrode and gold electrode, source and drain. A typical gap-width of ca. 40–60 nm has been achieved between the two electrodes. Au nanoparticles are placed randomly over the gap area. The formation of sulfide shell inhibits the "e" charge transfer from one nanoparticle to another, ie the so-called hopping phenomena. Why isn't there a "verb" in the sentence starting with "in each sense"?