Carbon nanodots (CDs) have been synthesized at gram scale with a high yield (41.8%) by carbonization of sucrose with oil acid in one simple step. The synthesized CDs are monodisperse with a narrow size distribution (average 1.84 nm in size), and show a high fluorescence quantum yield (21.6%) without passivation. The PL intensity of the obtained CDs is pH independent over a range of 2-8. Besides, their PL intensity remains unchanged even after six hours of UV excitation and six months of storage, exhibiting excellent stability. The obtained CDs have been used for cell imaging. The results demonstrate that the prepared CDs have great potential for real applications.

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Herein, iron and nitrogen co-doped carbon dots (Fe-N-CDs) were synthesized through a solvothermal method assisting with the microwave synthesis system for the first time. Multiple techniques were employed to characterize the properties of the obtained particles. The emphasis of current work was the confirmation of their intrinsic peroxidase activity due to the Fe doping, which is similar to natural ferriporphyrin. Through catalyzing the oxidization of 3,3',5,5'-Tetramethylbenzidine (TMB) in the presence of HO, the Fe-N-CDs exhibited a superior catalytic performance over horseradish peroxidase (HRP), suggesting their potential applications in catalytic area. Furthermore, the Fe-N-CDs were coupled to antibody as the biocatalyst instead of HRP (commonly used in enzyme-linked immunosorbnent assay (ELISA)). Results of carcinoembryonic antigen (CEA) determination demonstrated the feasibility of this approach, a detection limit as low as 0.1pg/mL within 5min has been achieved. These advances may trigger research interest in Fe-N-CDs and their new applications in various fields.

Carbon dots (CDs) emerge as excellent fluorescent nanomaterials, but the full exploitation and application of their exceptional properties in the development of fluorescence assay are still rare. In this work, cationic carbon dots (C-CDs) covered with plenty of positive charges on the surface were synthesized through a facile ultrasonic method. Negatively charged hyaluronic acid (HA) caused the aggregation of positively charged C-CDs and neutral red (NR) along its linear chain via electrostatic adsorption, leading to a remarkable Förster resonance energy transfer (FRET) from C-CDs to NR. However, the presence of hyaluronidase (HAase) resulted in the enzymolysis of HA, as well as the liberation of C-CDs and NR. The corresponding change of fluorescence color from red to green-yellow afforded a reliable ratiometric assay for HAase. Also the ratio of fluorescence intensity for C-CDs (I525) to that for NR (I630) was used for quantitative detection of HAase. The proposed sensing system was easily operated in aqueous media with a detection limit of 0.05 U/mL. This strategy provides a new approach for the wider application of some special CDs in detecting biomolecules.