Advances in smartphone assisted sensors for on-site detection of food safety based on fluorescence on-off-on mode: A review

As technology continues to advance and new application scenarios emerge, accurate and rapid on-site detection sensors are essential for monitoring and control the quality and safety of food. The excellent photography and image processing capabilities of smartphone has greatly facilitated the miniaturization, integration, and visual monitoring of sensors, making them essential tools for portable real-time determination. The "on–off-on" fluorescence sensor has garnered significant attention due to its remarkable features, including high sensitivity, excellent selectivity, strong anti-interference ability, and customizable probe structure. In this context, portable sensors with intelligent analysis and sensing systems have been extensively reported according to the "on–off-on" fluorescent signals, and highlight their immense potential and value in various fields. However, to date, a comprehensive review of smartphone-based on-site detection platforms driven by the "on–off-on" fluorescence mechanism remains absent. This review aims to fill this gap by providing an elaborate explanation of the "on–off-on" fluorescence response process, along with a detailed introduction to commonly used fluorescent materials and their underlying design principles. Furthermore, the latest applications of portable sensors based on the "on–off-on" fluorescence approach in detection of food safety are thoroughly reviewed. Finally, an in-depth analysis was conducted on the challenges and future development directions of the smartphone based sensing systems. This review aims to provide a valuable theoretical basis for comprehending and designing portable sensors, ultimately contributing to more effective and accurate real-time detection of pollutants.