Carbon Dots with Continuously Tunable Full-Color Emission and Their Application in Ratiometric pH Sensing

TLDR

The study aims to exploit the excitation‑dependent full‑color emissions of carbon dots to enable novel applications. The authors synthesize two types of carbon dots via a mild one‑pot reaction from chloroform and diethylamine and use a simplified energy‑level diagram to explain how surface functional groups control their emission. The resulting carbon dots are highly stable, reproducibly tunable, and their surface C═O and C═N groups create new energy levels that allow continuous full‑color emission, which the authors use to construct a ratiometric pH sensor that accurately measures intracellular pH and assists in cancer diagnosis.

Abstract

Two types of carbon dots (C dots) exhibiting respective excitation-independent blue emission and excitation-dependent full-color emissions have been synthesized via a mild one-pot process from chloroform and diethylamine. This new bottom-up synthetic strategy leads to highly stable crystalline C dots with tunable surface functionalities in high reproducibility. By detailed characterization and comparison of the two types of C dots, it is proved concretely that the surface functional groups, such as C═O and C═N, can efficiently introduce new energy levels for electron transitions and result in the continuously adjustable full-color emissions. A simplified energy level and electron transition diagram has been proposed to help understand how surface functional groups affect the emission properties. By taking advantage of the unique excitation-dependent full-color emissions, various new applications can be anticipated. Here, as an example, a ratiometric pH sensor using two emission wavelengths of the C dots as independent references has been constructed to improve the reliability and accuracy, and the pH sensor is applied to the measurement of intracellular pH values and cancer diagnosis.