Over two years, PhyToVALUE conducted experiments with three representative algal species (Chlorella vulgaris, Acutodesmus obliquus, Arthrospira platensis).
- Screening of methods: Among several fluorescence approaches, the OJIP transient was identified as the most sensitive. A novel diagnostic signal, the K peak, was discovered, specific to NH₃ stress.
- Recovery and discrimination: Cultures could recover from NH₃ exposures up to ~150% of the inhibitory concentration (EC₅₀). A Lasso regression model was developed to discriminate NH₃ stress from other stressors (light, heat, metals), achieving reliable predictions even under complex conditions.
- Device development: A low-cost, open-source fluorometer (MultiJIP) was built, with dual-wavelength LEDs, variable excitation intensity, and a graphical interface. The system enables real-time estimation of NH₃ toxicity and will be released openly via GitHub.
- Application to cultivation: The method was validated in fed-batch cultures under simulated diurnal light cycles, confirming feasibility under realistic dynamic conditions. While full closed-loop control was not implemented, the monitoring framework was proven.