A Smartphone Integrated Ratiometric Fluorescent Sensor For Point-of-Care Testing Of Fluoride Ions

Fluoride is a very important trace element in human body.With the development of fluorine chemistry,fluoride plays an increasingly important role in human production and life.However,the discharge of a large amount of fluoride into the environment will pose a significant threat to environmental safety and food safety.Fluorosis is caused by excessive fluoride in the body.The most common diseases are dental fluorosis and skeletal fluorosis.Its main symptoms are yellowish-brown patches on teeth,painful deformed bones,curvature of the spine and,in severe cases,complete incapacitation or death.Considering the wide distribution and high toxicity of fluoride ions,it is of great significance to develop a method for real-time detection of fluoride ions in the field for public health,environmental protection and food safety evaluation.In this paper,the calcein-quantum dot-europium ion(calcein-QDs-Eu³⁺)sensing system is composed of calcein（green emission）and Zinc Cadmium Selenium/Zinc sulfide Quantum dots（Zn Cd Se/Zn S QDs）（red emission）.When fluorine ions are added to the reaction system,the green fluorescence of calcein is restored and the fluorescence switch is turned on due to the stronger binding between fluorine ions and Eu³⁺.However,the red fluorescence of quantum dots is not affected by fluorine ions,and the fluorescence of the reaction system changes from red fluorescence to green fluorescence.Based on this,a ratio fluorescence strategy was developed for fluoride detection.The linear range of fluoride ion detection was 0.05-1.5m M,and the detection limit was as low as 11.2μM.The ratio fluorescence method makes the system have obvious fluorescence color change,eliminates the external environment interference,and improves the detection accuracy.Compared with other ions,Eu³⁺tends to bind with fluorine ion,and the sensor system has good selectivity.On this basis,test paper and hydrogel which can be used for point-of-care testing（POCT）were further prepared.In order to further improve the detection sensitivity,realizes the quantitative analysis,a smartphone with color scanning APP for reader and signal analyzer,used for the natural samples（tap water,drinking water and lake water）of fluorine ion in POCT testing.The method has high specificity and sensitivity,simple operation and rapid detection.It has great application potential in environmental protection and food safety evaluation.