Specialized nanoparticles known as monolayer-protected clusters (MPCs) were affixed with metal selective crown ether (CE) functional groups and assembled into novel thin films to form potential metal ion sensing materials. Films of MPCs modified with potassium specific 15-crown-5 ligands (CE-MPCs) were successfully assembled using both dithiol linkages and ester-coupling reactions. Film responses to potassium are observed spectroscopically as the manifestation of changing interparticle spacing within a film in the presence and absence of potassium. Growth dynamics, film structure, and metal response are examined. Additionally, the important role of flexibility, especially in the interconnectivity of the CE-MPCs within the film and between the CE groups themselves, is experimentally identified.