An intelligent smartphone-gel fluorescent sensing platform for on-site detection of slight pH variation in food...

The pH value in beverages is not merely a simple indicator of acidity and alkalinity. It is a key parameter that affects the sensory characteristics, nutritional value, shelf life, health effects, and production process of the beverages. Proper pH control is essential for producing high-quality, safe, and well-received beverages that consumers trust. Therefore, it is highly necessary to establish a convenient, rapid, and accurate pH-responsive fluorescence sensing platform. Herein, a multifunctional pH-responsive fluorescent probe (NPC) based on the intramolecular charge transfer (ICT) process was designed and synthesized. While the spirooxazolidine switching mechanism is well-established, the core innovation of this work lies in the synergistic integration of this molecular probe with an agarose gel matrix and a smartphone-based portable detection device. With the help of a smartphone-gel fluorescent sensing detection platform, probe NPC achieved fluorescence and visual dual-modal analysis of slight pH variations in beverage samples. The agarose gel indicator labels have a good linear relationship within the pH range of 5.00-7.00, enabling the rapid, accurate, and quantitative detection of slight pH variation in beverages. Moreover, it had an excellent recovery rate (95.7-106.7%) and low relative standard deviation (RSD) values (<3.52). Beyond food analysis, the moldability of the gel and the probe's reversible fluorescence response enabled its extension to security applications, including information encryption and 3D anti-counterfeiting structures. In addition, the excellent optical and fluorescence properties exhibited by probe NPC under both liquid and semi-solid conditions make it promising in high-end security fields such as information encryption and 2D/3D anti-counterfeiting applications.