Development of an image-based fluorometer with smartphone control for paper analytical devices

This work describes the construction and evaluation of a fluorometer for use in paper analytical devices, using a smartphone to operate the instrument and to perform real-time image-based detection. In this approach, a circular PAD containing twenty analytical plates is rotated at 18° increments under a UV LED source, providing a sequential irradiation of plates and the detection of the luminescence with a lab-made application, capable of automatically identifying the analytical zones and collecting the RGB intensities from the selected pixels. As a proof of concept, the fluorometer performance was evaluated for the determination of quinine in beverages and riboflavin (B2 vitamin) in supplements. Quinine, which is less photoreactive, provided steady-state signals, while riboflavin, which rapidly degrades under UV photons, presented transient responses for RGB detection. For both analytes, linear calibration ranges ( R 2 > 0.99) were observed from 2.0 mg L −1 to 10.0 mg L −1 with limits of detection estimated at approximately 1.0 mg L −1 . Nevertheless, it was demonstrated that successive additions of standard solutions to a single analytical plate of PAD could enhance the signal-to-noise ratios for less concentrated samples, acting as a pre-concentration step. In addition, suitable deviations for the signals ( ca. 4.0%) and the absence of systematic errors for most samples (9 out of 11), when compared with a reference method at 95% confidence level, indicates that the proposed strategy is precise and accurate enough to be used as analytical tool for fluorescence detection in PAD. This work describes the construction and evaluation of a fluorometer for use in paper analytical devices, using a smartphone to operate the instrument and to perform real-time image-based detection.