Carbon Dioxide-Driven Coupling in a Two-Compartment System: Methyl Red Oscillator

Strategies for designing autonomous oscillatory systems have gained much attention in the past few decades. A broadly accepted and used strategy for the generation of forced oscillations in the originally non-oscillatory subsystems is to couple a pH (driving) oscillator to a pH-sensitive substance (forced oscillatory subsystem) in a one-compartment system. The forced oscillatory subsystem comprises pH-sensitive components, which inevitably generate negative feedback and affect the characteristics of the driving oscillatory system. Here, we present a different approach by separating the driving and forced oscillatory systems into a two-compartment system using a silicone membrane, and the forced oscillations of the absorbance of a pH-sensitive chemical species (methyl red dye) were realized by the transport of carbon dioxide through the membrane generated periodically by the driving pH oscillator. The transported carbon dioxide produced the pH change in the separated compartment by carbon dioxide-hydrogen carbonate-carbonate equilibria and created forced oscillations of a pH-sensitive chemical species manifested in the oscillation of its absorbance at a fixed wavelength. This approach avoids any feedback from the forced oscillatory system to the driving system via the cross-membrane transport of the chemical species from the forced to the driving oscillatory system. Additionally, we present that this carbon dioxide coupling to the methyl red dye can be used to estimate the carbon dioxide content in both liquid and gas phases.