Looking at the best sensor extinction spectrum (Fig. ), it is interesting to note that only the LSPR-dominated peak responds to hydrogen, whereas the other peaks have lower LSPR contributions and are therefore less sensitive to changes in the refractive index of the nanodisks (Supplementary Figure ). This finding further corroborates our interpretation of the origin of the SLR peaks above. Finally, to appreciate the role of SLR excitation in obtaining sensors with high FoM, we also calculate the optical spectra of the best sensors single-particle counterpart (i.e., similar nanodisk parameters but not in array). As shown in Supplementary Figure , the isolated nanodisk features comparable Δλ peak , but suffers from an expansive FWHM of 498 nm, which drops its FoM to 0.07.