One-step synthesis of self-doped carbon dots with highly photoluminescence as multifunctional biosensors for detection of iron ions and pH

The nitrogen doped carbon dots (C-dots) with highly photoluminescence (PL) are synthesized using m-aminobenzoic acid (MAC) as the only precursor by a simple, one-step hydrothermal method. The NH2 groups of MAC have been used as nitrogen source to dope C-dots. The synthesized nitrogen doped (N-doped) C-dots present an unexpectedly large quantum yield of 30.7% and possess an essentially crystalline nature and desirable functional groups. More important, the C-dots can serve as multifunctional fluorescence nanosensors to detect pH and Fe3+. The fluorescent intensity of the C-dots increases dramatically as pH increases from 2 to 10. The fluorescent paper with C-dots coated for visual detection of pH by naked eyes has been successfully prepared. Moreover, the C-dots are employed for assaying Fe3+ based on direct interactions between Fe3+ and COOH and NH2 groups of C-dots. Under the optimal condition, a linear relationship between the decreased fluorescence intensity of C-dots and the concentration of Fe3+ is established in the range from 0 to 1.6 μM. The detection limit is as low as 0.05 μM, suggesting a promising assay for Fe3+. The results reported here provide a new approach for the design of N-doped multifunctional florescent sensor.