Plasma modified POF sensors for in situ environmental monitoring of museum indoor environments

A cumulative sensor for in situ monitoring of H2S vapors in museum showcases based on plastic optical fiber (POF) has been developed. H2S is responsible for the tarnishing of silver artifacts, so monitoring their total exposure over time to sulfide rich atmospheres can help in choosing the correct display procedure and, consequently, lead to improvements in their conservation. The sensor working principle is based on the modulation of the guided light intensity following a chemical reaction between a thin silver layer deposited onto the fiber core and the sulfide compounds to be detected. The proposed approach for the sensor fabrication requires the optimization of a two-step process: (1) etching of the fiber cladding to expose the core; (2) plasma deposition of a silver thin film onto the PMMA core. Silver was chosen as the sensitive element, since in the presence of H2S, it starts reacting immediately and loses its brightness with time proportionally to the concentration of the aggressive gas. Some prototypes of the proposed sensing system have been produced and tested in laboratory demonstrating the capability to detect H2S at concentrations of few part-per-billion (ppb).