Smartphone-based fluorometer for pH detection using green synthesized carbon dots

Abstract As a group of heavy-metal-free fluorescent nanomaterials, carbon dots (CDs) have recently received a growing interest as they have high optical absorption activity and are chemically stable, biocompatible, and less toxic. In this paper, the green synthesis of stable CDs by hydrothermal and pyrolysis methods from Parmigiano-Reggiano is performed. An intrinsically emitted fluorescence results from simultaneous generation and the surface passivation of CDs by the mentioned techniques. The responses of hydrothermal CDs to pH occur by emission wavelength at 430 nm under 365 nm excitation. When the pH is increased from 2–12, its emission fluorescence intensity will be reduced. The pH was also analyzed real time by developing a smartphone-based portable recognition platform consisting of an instrument and a self-designed APP called “Image Analyser”. The fluorescence color change of CDs caused by the pH was recorded by the camera of the smartphone and color of pictures was analyzed by APP. The results of both methods are similar, so the CDs based recognition platform are highly practically and efficient tool as they could analyze pH with outstanding functionality, as examined in this study in different samples.