Nitrogen and Sulfur Co-doped Carbon Quantum Dots for Detecting Fe(3+), Ascorbic Acid and Alkaline Phosphatase Activities.

A method utilizing nitrogen-doped and sulfur-doped carbon quantum dots (N, S-CQDs) as fluorescent probes for the rapid detection of Fe, L-ascorbic acid (AA), and alkaline phosphatase (ALP) was presented. The fluorescence intensity of N, S-CQDs nanoprobes can be rapidly and efficiently quenched by Fe and based on the fluorescence "turn off-on" characteristic of N, S-CQDs nanoprobes, the fluorescence signals of the N, S-CQDs/Fecan be recovered after the addition of AA. By coupling a fluorescent nanoprobe to an enzyme and L-ascorbic acid-2-phosphate (AA2P), a green, simple, rapid and effective fluorescent analytical method for the determination of ALP was developed. The prepared N, S-CQDs showed high sensitivity and selectivity to Fe, AA and ALP with the detection limit of 0.42 μM, 12.7 nM and 0.017 U·L and their optimal concentration ranges were10-600 µM, 10-200 μM, 0.18-54 U·L, respectively. The fluorescence quantum yield of N, S-CQDs (0.2 mg·mL) at 393 nm excitation wavelength was 4.41%. Additionally, the fluorescent nanoprobes have been employed to successfully measure ALP in serum samples. It is expected that the established method may offer a new approach for biomolecular detection in clinical diagnosis and pharmaceutical analysis.