Development of a Piezoelectric Sensor for Gas Detection Using a Silver(I) Coordination Polymer

Sensors for the detection of volatile compounds are a relevant topic of research and development as they find applications in monitoring the environment, in industry, in health care and also in aroma classification. Gas detectors are extremely important for accident prevention, because some types of substances, when inhaled, are harmful. Quartz crystal microbalance working with sensors covered with an organic sensitive layer produce oscillation frequencies that vary from the interaction with volatile gases. Sensing specificity is achieved by chemically modifying the surface of quartz sensors, and in this sense, polymers are materials that are successfully employed. The objective of this work was the development of a modification of piezoelectric sensors applying the coordination polymer silver(I) ${[Ag(bipy)]_3cdot(trim)cdot 8(H_2O)cdot(CH_3OH)}_n$ for sensing ammonia in gas phase using a low cost and open source microbalance; it transmits signals in real time to a software developed for data analysis and storage. Different conditions were studied and tested for the sensing of the analyte and for the formation of the film on the surface of the sensor, exploring different deposition methods such as spin coating, dip coating and casting. This polymer was chosen because the sensor surface is also covered by silver metal, which can provide a greater interaction between the sensor and the polymer under study, in addition to having specific interactions with the analyte of interest, such as the solubilization of the polymer in ammonia, which may indicate a doorway to new chemical reactions. A coordination polymer is constructed from the interaction between metallic cations and ligands capable of acting as a bridge between metallic centers in an arrangement that extends uni-, bi-, or three-dimensionally. The presence of the metal–ligand chemical bond in coordination polymers confers advantages over purely organic polymers. This is a promising sensing technique taking into account that the quartz crystal used in the microbalance has an affordable value, can be discarded or reused, and is easy to replace, in addition to allowing exploration of the innovation and application of coordination polymers and the Maker culture. It was possible to carry out the proof of concept of the microbalance developed by Professor Dr. Luiz Marcos de Lira Faria and the application of the silver(I) coordination polymer synthesized by the research group coordinated by Profª. Dra. Dayane Mey Reis.