Smartphone-Based Quantitative Fluorescence Detection of Flowing Droplets Using Embedded Ambient Light Sensor

The detection of fluorescent droplets on the smartphone-based platforms is normally limited by several aspects such as the imaging quality, automaticity, and accessibility. To address the issues, the smartphone-embedded ambient light sensor, which has shown the advantages including high accuracy, low noise, easy and reliable integration, becomes more and more noted to detect the light intensity variation. In this study, we develop a low-cost and portable smartphone-based platform using the embedded ambient light sensor for flowing fluorescent droplet detection. This platform is simply assembled with a 3D-printed holder and a light-emitting diode (LED) light source powered by the smartphone. Based on the Android system, two applications are self-developed for the performance test and fluorescent droplet detection respectively. After fabricating the droplet generator with off-the-shelf components, fluorescent droplets are generated under different flow rates of the continuous phase and characterized with both the microscopy and the presented platform. And 15 mu L/min was selected as the optimized flow rate of the continuous phase. Finally, the detections of the droplets in different fluorescein concentrations are performed in our smartphone-based platform to confirm its capacity of quantitative analysis. And a linear relationship between the intensity and the concentration with the R square larger than 0.99 is found. We believe that this platform will be a powerful tool in the areas including point-of-care diagnosis, environmental monitoring and food safety. More importantly, it can provide a new sight for the development of novel smartphone-based platforms beyond the embedded cameras.