Hydrogen bonding effect on pH-sensing mechanism of carbon dots

Recently, carbon dots (CDs) have received huge attention from scientists around the globe due to their unique properties, including excellent optical properties, good photobleaching, good biocompatibility, and ease of production. Notably, CDs exhibit novel results in pH sensing applications in water and intracellular environments due to their excellent anti-interfering ability and photostability. Herein, we successfully synthesized CDs by hydrothermal method using glucose and citric acid as precursors. The formation and breaking of hydrogen bonding play an important role in pH-sensing mechanisms of CDs. By using Raman signal of the hydrogen bonding in the photoluminescence (PL) spectra of CDs, we investigate here the effect of hydrogen bonding on the pH-sensing of CDs. It is expected that the mechanism of pH-sensing on the PL signal could be unraveled. As the results, the hydrogen bonding significantly reduced the PL intensity of CDs in a pH range of 7-11 but it did not influence the PL of CDs in higher pH conditions. Based on the interaction between hydrogen bonding and CDs, a new model for the pH-sensing mechanism of CDs was proposed. This work sheds new light on the mechanism of pH-sensing on the PL signal and suggests a new application of CDs in moisture and water sensors for air, soil, food, and commercial chemicals.