Lab-in-a-Phone: Smartphone-Based Portable Fluorometer for pH Measurements of Environmental Water

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Journal Article
IEEE Sensors Journal, 2015, 15 (9), pp. 5095 - 5102
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© 2001-2012 IEEE. A novel portable fluorometer combining the attributes of a smartphone with an easy-fit, simple and compact sample chamber fabricated using 3-D printing has been developed for pH measurements of environmental water in the field. A color filter attached over the camera white light light-emitting diode selects an excitation band centered around \lambda \sim 450 nm with a 3-dB bandwidth, \Delta \lambda \sim 21 nm. An application-specific, temperature-stable probe based on the 4-aminonaphthalimide fluorophore was synthesized to absorb at this wavelength while emitting in the green region of the visible spectrum. The green emission is readily detected using the smartphone camera and a simple red-green-blue Android application. Suppression of the green emission increases with increasing pH enabling a straightforward pH sensor. The system was calibrated against a commercial spectrofluorometer and pH measurements were taken at various locations around Sydney. The results were then compared directly with those obtained using conventional electrode-based measurements. The data can be stored in the phone's available memory or transmitted by phone back to base for further real-time analysis.
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