Polyaniline functionalized electrochemically reduced graphene oxide chemiresistive sensor to monitor the pH in real time during microbial fermentations

Here we report potentiometric and chemiresistive pH sensing performance of polyaniline functionalized Electrochemically reduced graphene oxide (ERGO-PA) to monitor pH change in Lactococcus lactis fermentation continuously in real time. We found that polyaniline functionalized graphene oxide as such, cannot be used in a fermentation process to monitor pH. A lot of interference was observed from electrochemically active redox species that are produced during the bacterial growth. We have successfully employed a simple Nafion coating on top of the ERGO-PA to avoid interferences. The Nafion coated electrodes show a good sensitivity of 55 mV/pH (pH 2-9) and 1.71 Ω/pH (pH 4-9) for potentiometric and chemiresistive sensor measurements, respectively. Real time pH measurements of Nafion coated ERGO-PA in a L. lactis fermentation show that it can be used for continuous pH measurements in complex biological growth media. Effectiveness of ERGO-PA-NA solid state chemiresistive pH sensor in complex fermentation process shows that reference less solid state micro sensors can be fabricated and could be used in e.g. multi micro bioreactor screening platforms.