pH-driven dual sensing: A single fluorescent probe for real-time food spoilage tracking and microfluidic sorting of acid-producing bacteria.

Real-time monitoring of microbial metabolic activity is essential for early detection of food spoilage and industrial strain selection. Conventional methods, however, suffer from poor timeliness, sensitivity, and throughput due to limitations of existing fluorescent probes. To overcome these, we developed a novel quinoline-based probe, AXE, synthesized via a one-step condensation. AXE shows a highly sensitive, linear response within the key metabolic pH range (5.5-8.0), resists 26 classes of interferents, and responds within 2 min. It successfully tracked the characteristic "V-shaped" pH trajectory of spoiling pork at 4 °C. Coupled with droplet microfluidics, the platform efficiently isolated acidogenic Bacillus from complex samples (0.75% positivity rate), identifying 11 high-performance isolates that lowered medium pH below 5.0. AXE serves as a versatile dual-functional platform for real-time food freshness assessment and high-throughput microbial screening.