A self-calibrating logic system and oxidase-based biosensor using Tb3+-doped carbon dots/DNA conjugates

Tb3+-doped carbon dots (Tb3+@CDs) were prepared in a facile hydrothermal method by using ammonium citrate as carbon source and Tb3+ as dopant. A 15-bp GT-rich single-strand DNA (ssDNA) was introduced to sensitize Tb3+ via the antenna effect for generating two fluorescence signals (CDs and Tb3+), forming a conjugate of Tb3+@CDs/ssDNA. The ratiometric fluorescence of Tb3+@CDs/ssDNA could be reversibly regulated by Ag+ and Cys, in which the fluorescence peak at 546 nm of Tb3+ could be switched to "On" or "Off" as the signal indicator while the fluorescence peak at 444 nm of CDs remained constant as the build-in reference. The proposed Ag+/Cys-mediated reversible fluorescence changes in Tb3+@CDs/ssDNA was also proven for the design of a self-calibrating ratiometric fluorescence logic system. By integrated with the specific reaction between H2O2 and Cys, Tb3+@CDs/ssDNA was applied for ratiometric fluorescence detection of H2O2. More importantly, the sensing strategy could be further successfully extended to the monitoring of H2O2-produced oxidase-related reactions, such as GOx-biocatalyzed oxidation of glucose (the limit of detection: 0.06 mu M) and was well applied in rat serum compared to commercial kits. This work unveiled a novel ratiometric fluorescent design, which is cost-effective, simple to prepare and easy-to-use without chemical modification or fluorescence labeling.