A redox modulated ratiometric fluorometric method based on the use of dual-color carbon dots for determination of the activity of enzymes participating in ascorbic acid-related reactions.

A turn-on ratiometric fluorescent assay is described for the determination of the activity of enzymes participating in ascorbic acid-forming reactions. Blue-emitting carbon dots (bCDs; with excitation/emission wavelength at 380/450 nm) serve as fluorescent indicator. Their fluorescence is reduced by Fe ions via an inner filter effect. Yellow-emitting CDs (yCDs; with excitation/emission wavelength at 380/550 nm) serve as internal reference because their fluorescence is insensitive to Fe. Upon exposure to ascorbic acid (AA), Fe is reduced to Fe. Hence, the fluorescence of the bCDs is restored. Thus, enzymes participating in AA-related reactions such as α-glucosidase (α-Glu) and alkaline phosphatase (ALP) can be determined. α-Glu activity was quantified in the range from 0.13 to 6.70 U mL, and ALP activity was determined between 2.0 and 130 U L. Endowed with excellent sensitivity, selectivity and low background signals, the method may also be used to screen the inhibitors of α-Glu and ALP. Graphical abstractSchematic representation of a redox modulated ratiometric fluorometric method based on the use of dual-color carbon dots for determination of the activity of enzymes participating in ascorbic acid-related reactions. Blue-emitting carbon dots (bCDs) serve as fluorescent indicator while yellow-emitting CDs (yCDs) serve as internal reference.