Plasmonic coupling is a fascinating fenomena occurring between neighboring metal nanostructures. We report a straightforward approach to study it macroscopically by fabricating 2D networks of gold nanoparticles, interconnected with hygroscopic organic linkers. By controlling the humidity we tune the interparticle distance to reversibly trigger plasmon coupling collectively over several millimeter.Colorimetric sensors are devices which undergo macroscopic changes in their UV-Vis absorbance or fluorescence characteristics upon interaction with the target analyte. Such changes typically fall within the visible light region and can be so dramatic to be easily perceived by naked eye. 1 Hitherto, such kind of devices, featuring three-dimensional structures, have been employed for the detection of various compounds in solutions 2-4 as well as in gaseous state 5 . Noble metal nanoparticles (NPs), which can be synthesized in solution with precise control over shape, size and optical properties 6-10 , represents an extremely versatile platform for the fabrication of such devices. 11 In solution, gold nanoparticles (AuNPs) are one among the most exploited and best performing scaffolds for sensing because of their high chemical stability, which is achieved upon functionalization with various functional stabilizing shells 12 , and their optical properties, which are extremely sensitive to changes in the local environment. Isolated AuNPs exhibit distinct optical properties arising from their localized surface plasmon resonance (LSPR), 13 which depends on their size and shape, as well as on the refractive index of their environment. However, when the AuNPs are in close proximity between each other (i.e. with spacing of a few nm), a coupling of the LSPR takes place, dramatically modifying the optical properties and therefore altering their macroscopic colour [14][15][16][17][18] . Hitherto, this phenomena has just been exploited for the detection of analytes in solution, where the AuNPs are dispersed or free to move and aggregate, 19 while sensing of gaseous compounds with dry NPs films is usually achieved through modifications of the refractive index in close proximity to the particle's surface 20 . The latter approach suffers from a poor sensitivity and can only be employed for sensing analytes which exhibit a very different refractive index compared to the one of the shell used for AuNPs stabilization. An interesting strategy to enhance the sensitivity in solid films could rely in the fabrication of dynamic structures in which the interaction with the target analyte affects, at the same time, refractive index and interparticles distance. However, the fabrication of stable structures, providing a predictable and reproducible optical output, allowing to study and to disentangle the two contributions, still remain elusive. In contrast with previous works reporting on unstable superlattices relying on evanescent noncovalent interactions, 21 here we report on an unprecedented strategy for the fabrication of humidity sensors based ...

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