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 μ 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.