Study of Liquid Film Thickness for Gas Phase Odor Biosensor

Abstract

In recent years, several gas-phase odor biosensors have been developed. Sensitive cells and multiple sensing elements were investigated for enhancing the performance of those biosensors. The thickness of the liquid layer that covers the cells, however, has rarely been so far explored. Recently we utilized the feedback control method to maintain a constant liquid film. Now we intended to step further about the alteration and estimation of this liquid film. Here, we developed a gas phase odor biosensor with variable liquid film thickness. The liquid layer thickness change was reflected as the impedance change between two electrodes. Thinner liquid film always resulted in greater response and faster peak time. For realizing such a thin liquid film state, withdrawing the buffer solution step by step was more preferred. Furthermore, the sample concentration dependency curves under normal and thin liquid layer conditions proved thin liquid film improved response evidently. Moreover, the weakened stability caused by thin liquid film was explained. Finally, we calculated the liquid film thickness according to the feedback control signal and validated the estimation result by manual operation. It revealed a steady liquid film thinner than 100 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> was implemented in this system. This study demonstrated the advantages of thin liquid layer and provided an access to estimation and fine adjustment of liquid film thickness in gas phase odor biosensors.