pH is a critical indicator of cell and tissue health - deviations from neutral pH are observed in a range of human diseases including cancer, infection, inflammatory processes and hypoxia. Biorefineries in which microorganisms are employed to convert feedstocks and waste products into useful products often employ real-time monitoring of pH with feedback control to maintain optimal cell density and product yield. In this study Gabe investigated the stability and reliability of our fluorescent pH nanosensors for real-time pH monitoring before and after "aging" at elevated temperatures and in the presence of different interfering compunds. After showing that the particle scaffold was highly stable over time and across temperatures, we then employed fresh or aged sensors to monitor the pH of E. coli cultures during log-phase growth, in comparison to a traditional glass electrode. We learned that the choice of specific dyes and attachment chemistries need to be carefully chosen to support long-term nanosensoe stability. Watch this space - plenty of new opportunities for accurate, real-time pH sensing!