Construction of integrated and portable fluorescence sensor and the application for visual detection in situ

The development of portable and low-cost fluorescence sensors is significant for on-site detection. Herein, a novel fluorescence sensor integrating power source, light source, filter, sample cell and smartphone was constructed. The model of fluorescence sensor was designed by using Autodesk Computer Aided Design (CAD) software, and printed with 3D printing technology, followed by assembling with various components. With advantages of convenient carrying, good stability, wide applicability and low cost, the fluorescence sensor showed great adaptability for on-site visual detection. Nitrite was chosen as the model of analyte, and ratiometric fluorescent probe (B/R-CDs) was employed as the identification and signal element for detecting nitrite. With the increase of nitrite concentration, the fluorescence intensity of B/R-CDs at 460 nm decreased, while that at 615 nm kept stable. Therefore, the fluorescence color of B/R-CDs changed from blue to red. By using the portable sensor to collect RGB value of fluorescence color, the R/B channel values showed a linear relationship with nitrite concentration in 2.5–600 µM, with detection limit of 0.8 µM. Then the fluorescence sensor was used to detect nitrite in preserved meat and pickles, and recovery rate was among 94.0%−105%. The detection results were consistent with those of fluorescence method and spectrophotometry. This work provides a novel detection device for on-site analysis, and also offers an effective approach for developing miniature fluorescence sensors.