Our challenge was to find a cheap and simple measurement device that could be replicated in our labs to measure the consumption of CO2 by Synechococcus sp. with the objective of quantify in real time the metabolic rate of our genetically modified cyanobacteria (Image 1).
We adapted a pH electrode to make it sensible to changes in CO2 concentrations in an aqueous solution.
An electrolyte chamber was placed inside the electrode to enable the reading of voltage changes that were proportional to changes in CO2 concentrations (Image 2) (for more information regarding the protocol for this device, review the document “Determination and balance of CO2 in the cyanobacteria system” available at Experimentation).
The device we emulated is called “The Severinghaus Electrode”. This design was consulted in a scientific article and it is based on the equilibria reactions of carbon dioxide in aqueous solutions (equation 1).
It is important to mention that the pH in the solution of the middle of the chamber is completely dependent on the pCO2 if the temperature and pressure of the system remain constant.
The membrane used to cover the electrode bulb was made up of silicon sealant. It was previously prepared by spreading the sealant in a Teflon pan and leaving it to dry for 2 hours. The thickness of the membrane was around 1 mm (Image 3).
Our electrode had a plastic crown that prevented the bulb from breaking and created a considerabe space between the electrode bulb and the membrane we prepared. However, it is important to have as minimum space as possible between the electrode and the membrane filled with the electrolyte solution to get accurate readings. So we designed a neoprene gasket (cut by laser in neoprene sheet) that could hold the membrane in place and reduced the space between the electrode, the membrane and the plastic crown (Image 4).
Image 5 ilustrates the final footage of the dissolved CO2 sensor that we designed for our cyanobacteria system.
After the calibration process, we obtained an accurate curve (R2=0.9393) which represents how voltage changes in relation with the magnitude of CO2 dissolved in the system, which was actually very useful to quantify the metabolic capacity of Synechococcus sp. for the capture of CO2.