Physicochemical and statistical characterization of gas-sensing behaviors of resonator sensors with carbonaceous films prepared by rf-sputtering of aromatic and hydrophilic biomolecules

Quartz crystal resonators coated with gas-sorptive films were characterized by analyzing their structures and their organic gas-sorption behaviors, which were then studied using statistics and computational molecular simulations. The films had carbonaceous structures that were prepared by radio-frequency (rf) sputtering of aromatic biomolecules, such as cytosine and lignin. These films had been compared with the rf-sputtered films of hydrophilic biopolymer of lignin and gelatin.The composition and morphology of each film governed the organic gas-sorption characteristics of the resonator sensors used for organic gas-sensing. The cytosine film, which was nitrogen-rich and layered, had a moderate affinity for the larger molecules of normal alcohols and acetate esters. The cytosine film is repulsive to positively-charged moieties of adsorbates. In contrast, the agarose film, which was nitrogen-poor and columnar, had a high affinity for small adsorbates with short hydrocarbon chains. Molecular flexibility of the adsorbate played an important role in the gas-sorption ability of the agarose film. Molecular dynamics simulation clarified that the weakly dipolar adsorbate-aggregate were immiscible in the cytosine adsorbent-aggregate because the collision mixture was prone to be instable. In practice, the cytosine-sputtered film had a higher gas-sorption ability for weakly dipolar species that have the longer hydrocarbon chains.