Fig. 1. Graphical illustration of MNHM etalon and its ingredients.

(A) Schematics of MNHM etalon under the humid and dry state of the surrounding. (B) Ligand exchange of AgNPs-OLA transformed to AgNPs-SCN. The aggregated nanoclusters form membrane pores that aid the penetration of gas into the hydrogel layer. Gray circle, Ag NP; dot with zigzag tail, OLA ligand; dot with straight tail, SCN ligand. (C) Swelling/contraction of chitosan hydrogel under the change of humidity condition. Yellow line, chitosan network; blue dot, water molecule; green dashed line, hydrogen bonding between the chitosan network and water molecules.