We systematically summarize the recent progress in the green synthesis and formation mechanism of CDs with the hope to provide guidance for developing CDs with the concept of green chemistry. In addition, we discuss and organize the current opinions on the fluorescence origin of CDs and the latest progress of CDs in fluorescence sensing applications.

Ratiometric fluorescence (FL) probes can eliminate the background interference and provide more accurate detection results than single emission intensity-based nanoprobes. Recently, carbon dots (CDs)-based ratiometric FL probes have received extensive research attention due to their excellent biocompatibility, water solubility, and multi-emission capabilities. In this review, we firstly summarize the construction strategies of CDs-based ratiometric FL probes, including physical mixing, nanohybrid, and dual-emitting CDs strategies. Additionally, we classify the sensing types of CDs-based ratiometric FL probes into five categories according to the difference in spectral variation caused by analytes: “single-response-ON”, “single-response-OFF”, “double-responses-ON”, “double-responses-OFF”, and “double-responses-Reverse” types. Finally, a thorough overview of CDs-based ratiometric FL probe applications in ions, molecules, pH, and temperature sensing is provided. We believe this review can show the latest research progress of CDs-based ratiometric FL sensing fields and provide perspectives on future developments for the construction of CDs-based ratiometric FL probes and their potential applications.

Tb-CDs were firstly prepared through one-step direct carbonization method for highly selective detection of TNP.

Carbon quantum dots (CQDs), a rising star family in photoluminescent (PL) nanomaterials, have been identified to have a core–shell structure with the nanocrystalline core of sp²-hybridized carbon clusters and the functional group formed shell of sp³-hybridized carbons, in which the core formation usually needs high-temperature carbonization. Herein, we develop a route to prepare CQDs on a large scale by using hydroquinone and ethylenediamine (EDA) as the precursors and the EDA-catalyzed decomposition of hydrogen peroxide at room temperature. The released heat from this highly exothermic reaction system can rapidly prompt the formation of the nanocrystalline core. The as-prepared CQDs in situ show green PL properties around 525 nm under excitation at 320 to 420 nm with the absolute quantum yield of 24.6%, and can find applications in visual analysis and other fields.

We summarize the construction methods and influencing factors of CDs-based composites and discuss their catalytic applications, including photocatalysis, chemical catalysis, peroxidase-like catalysis, Fenton-like catalysis and electrocatalysis.