Smartphone-based Portable Device for Rapid and Sensitive pH Detection by Fluorescent Carbon Dots

Abstract In the past few years, most studies have focused on smart substances that can respond to changes in the environment, as they can be appropriately applied in different fields, including biosensing, biotechnology, and drug delivery. Here, new fluorescent carbon dots (CDs) are synthesized by Terebinth by designing a simple and single-stage hydrothermal path, which facilitates the manufacture of CDs with no need for boring artificial methods, or using poisonous/costly solvents and starting substances. The method is used to concurrently form CDs and passivate their surface, which results in inherently emitted fluorescence. The study of the structure and optical features of the resulting CDs indicates blue emission at 440 nm, an average size of 4 nm, and a 3.2% quantum yield. The CDs respond pH-dependently ranging from pH 2-12. Increasing pH from 2 to 12 reduces the emission. Furthermore, a smartphone-based portable device (SPD) was designed to analyze pH real-timely, comprising a device and a self-engineered APP called “Fluorimeter”. The CDs-based fluorescence sensing system and the detection platform performed excellently in analyzing real samples, which demonstrated high potentiality to be applied in practical monitoring.