Green synthesis of carbon dots using the flowers of Osmanthus fragrans (Thunb.) Lour. as precursors: application in Fe and ascorbic acid determination and cell imaging.

In this work, dried flowers of Osmanthus fragrans Lour. were applied as green precursors to synthesize carbon dots (CDs) by a green hydrothermal method for the first time. The CDs showed strong blue fluorescence at 410 nm under 340-nm excitation with a quantum yield of approximately 18.53%. Furthermore, the CDs were applied for the sensitive detection of Fe. The linear response of Fe ranged from 10 nM to 50 μM with a limit of detection as low as 5 nM. In addition, other ions were used as competitive substances to explore the selectivity of CDs for Fe. The fluorescence quenching effect of Fe was much stronger, which demonstrated that the CDs had high selectivity for Fe and they can be employed for the selective detection of Fe. The potential fluorescence quenching mechanism between CDs and Fe was identified as the inner filter effect. The CDs were then used as a fluorescent sensor for the detection of Fe in water samples and human serum; the recovery range was 93.76-113.80% (relative standard deviation less than 0.79%). These results indicate that the CDs can be applied for the sensitive and selective detection of Fe in real samples. Moreover, on the basis of the redox reaction between Fe and ascorbic acid (AA), the CD-Fe system can be used as a fluorescent "off-on" sensor for the detection of AA with a limit of detection of 5 μM. What is more, because of their low toxicity and biocompatibility, the CDs can also be used for cell imaging and acted as a fluorescent probe for fluorescence imaging of Fe and AA in living cells. These results demonstrate that the CDs have great potential for application in the fields of sensing, bioimaging, and even disease diagnosis.