As an important control, we fabricated an array with similar geometry parameters (d = 124 nm, h = 20 nm, and t PMMA = 300 nm), but with the nanodisks dispersed quasi-randomly over the substrate rather than in a periodic lattice (Fig. and Supplementary Figure ). We compared the optical response of this control sensor exposed to H 2 pulses under similar experimental conditions as the periodic array. Consistent with the FDTD simulations (Supplementary Figure ), the control sensor exhibits comparable Δλ peak with respect to the H 2 concentration (Fig. ).